Video Analysis of Sports

Dane vs. Jordy: Who Does Higher Surfing Aerials?

2010-09-23T10:16:00.000-07:00

The biggest 2010 surfing event in the US was recently completed in perfect 6 foot waves at Trestles in Southern California. The surfing was innovative and exciting with technical and high flying performances, elevating surfing to a mesmerizing and progressive spectator sport.

This was the first surf event to use the new competition format, pitting the worlds top 32 surfers and 4 qualifiers against each other. If you want to find out more about the surfing World Championship Tour check out this video or head to the ASP Surfing website. The new format and fantastic waves brought the best out of many surfers on the tour.

Dane Reynolds and Jordy Smith were stand out performers, particularly in the air and that's where we want to go in this blog. Just like basketball slam dunk competitions, the higher the aerial maneuver the more exciting and better it is. Of course if the surfer does not land and ride out then it cannot count (similar to a missed basket in an attempted slam). The surfing judging criteria do not specify height in an aerial move as a criteria, but height above the wave definitely makes the move look more difficult.

In the video we have Dane and Jordy performing aerial moves at the Trestles Hurley Pro. Dane is first up and we will look at his first air. Jordy is third surfer up and we will look at his "Superman" air when his feet come off the board.

To compare these two aerial moves we will measure height above the top of the wave at the peak for the air. We will do this because the camera footage allows us to see both the surfer and top of the wave in the same image for both surfers.

To measure their height above the wave we have to make some assumptions. Firstly we need to estimate the length of their surfboards. We will use this length to scale the video and allow us to measure height. We will assume that the board Dane was riding was 6 foot 1 inch (73 inches) Al Merrick Proton that he refers to in this video. We will assume that Jordy is riding a 6 foot 2 inch (74 inches)board as he talks about here.

Take a look at the images below. First Dane and then Jordy.

To compare their aerial heights we measured the height of their hips above the wave. Dane and Jordy both get their hips just under 5 foot (60 inches) above the top of the wave. Dane may be a little higher, an inch or so, but as the video of these aerial moves was taken from different positions and with different fields of view, we need to allow for some error. So we will have to say that both got about the same height above the wave.

So who did better? The judges scored Dane's wave with this aerial in round 3 of the event as a 9.33 out of 10 and Jordy's wave with his "Superman" air, also in round 3, as a 9.60. A wave is not judge only on one move though(unless its the only move) and Jordy did bigger moves on the rest of his wave than Dane. So maybe height of an aerial move does factor into the judges scoring and in this case the judges scored both waves high because of the incredible amplitude that both surfers reach.

Of course surfing is not only about being in the air above the waves but also about the movement, flow, power and combinations on the face of the wave. The 2010 Hurley Pro at Trestles was not won by either Dane or Jordy, but rather by the master of surfing, Kelly Slater.

Kelly is currently leading the World Championship Tour ratings going for his 10th title, but Jordy and Dane (2nd and 4th respectively) are right in it to. We expect the surfing will continue to be as exciting as it was at Trestles with these three athletes pushing each other to greater heights and hope to be seeing and analyzing the first aerial move 6 foot above the wave.

Why is Nadal Serving Faster at the US Open 2010?

2010-09-08T11:15:00.000-07:00

From Rafael Nadal's first game of the US Open in 2010, there has been lots of talk about his improved serve speed. Although being the best player in the world, Rafa has never had the best serve or even one of the better serves in the game. This improved serving speed though, would put him into the same first serve speed range as Murray and Federer and make him even more threatening on hard court surfaces, the only surface on which he is not consistently dominant.

In the Wimbledon 2010 final against Tomas Berdych, Nadal had a 69% first serve percentage, averaging 115MPH, with a fastest serve at 127MPH. In his 4th round match at the 2010 US Open against Feliciano Lopez, Rafa hit 63% first serves in, averaged 118 MPH for his first serve and maxed out at 135MPH.

Although one game does not suggest a complete turn around, the stats listed above seem to be consistent for all matches that Nadal played in both Wimbledon 2010 and so far in the US Open 2010. The stats suggest that Rafa's serving percentage is a little lower in the US Open (4%), his average first serve speed is only slightly higher (3MPH) and only his fastest serve seems to be impressively different with an increase of 8 MPH.

Rumours abound as to how Nadal has improved his 1st serve speed. His coach Tony Nadal says he opened his grip more. Rafa himself says, nothing is different. John McEnroe seems to be completely flummoxed.

Looking at it this way maybe there is not much to be surprised about. Nadal has always used a lot of spin and control in his serve. This is good enough for the slower clay and grass courts and was good enough for the slower hard court of the Australian Open in 2009, but for the fast courts at Flushing Meadow, Nadal knows that a few fast serves and quick points will benefit his game more, saving his joints and energy.

Therefore we believe in everything Rafa and his uncle and coach Tony have said. He is not doing too much different except opening up his grip and attempting more flat and hard serves rather than spin. His 6'1 height and obvious strength suggest there is little reason that he cannot hit a 135MPH flat serve, if he attempts one. He may be losing a little accuracy and lowering his 1st serve percentage but if he wins the US Open 2010, it will all have been worth it.

Below is some slow motion video of Nadal serving during training. Watch the video and pause it just before he hits the ball.
Watch how his hand is gripping the racket and how the racket turns after he hits through the ball.

In the first three serves in this video Nadal hits across the ball, putting spin on his serve. We can see this by the way the racket turns after striking the ball. The last serve in the video seems to be a bit flatter and the racket turns slower and later. In all cases though the grip looks the same and fairly closed.

The video is from March 2009 and therefore probably does not show any changes that Nadal has made for the US Open 2010. It does show us that in the past Nadal has used a lot of spin and a closed grip. Flattening out his first serve on a few occasions therefore is the most likely explanation of his increased first serve speed at the US Open.

Comparing Federer's Between the Legs Shot

2010-08-31T14:43:00.000-07:00

Thats right Roger Federer did it again. A shot between the legs at the US Open for a winner. In 2009 he played this shot against Djokovic in the semi-final. This time it was a lower ranked player he beat with the shot, but the shot itself was still one of pure genius.

In 2009, after watching his shot against Djokovic, we discussed how Federer actually practices a between the legs shot, so that when he pulls it off in a match it cannot be described as lucky. He knows how to play this shot and is probably even trying to hit a winner, so that he is not caught out of position.

On this website we love to compare athletes and performances. Having two examples of Federer's between the leg shot allows us to do a quick comparison.

Both shots are played as Roger runs backward to retrieve a ball that was lobbed over his head.
Versus Djokovic, Federer plays his shot behind the baseline. Djokovic is standing up at the net, so Roger needed to beat him with power and place it just wide enough.
Versus Brian Dabul in 2010, he plays the shot further behind the baseline than the shot in 2009. This time his opponent stays at the baseline and placement is more important. He needed to go deep into the corner with the shot to wrong foot Dabul and keep the ball out of his reach on the baseline.
Both shots though need to be played with power and in both cases we can see how Federer sets up with his feet and plays the shot with a lot of wrist action to create speed on the ball.

Take a look at the video below. A comparison is made by John Mcenroe near the end.

Federer gives us a great opportunity to analyze perfection. He practices perfect mechanics all the time and shots come naturally to him in the match because of all his practice and analysis.

Keep using your video camera to analyze and compare your performances.

Measuring Michael Jordan's 1987 Slam Dunk Contest Vertical Leap

2010-08-23T16:37:00.000-07:00

Comparing the vertical leap of past winners of the slam dunk contest would give us great insight into who really has the best dunk. So time for a Video Analysis of Sports Vertical Leap Dunk Off.

Last week we discussed how we could use broadcast footage of the slam dunk contests to measure the vertical leap of each player during the dunk. We looked at Vince Carter's 2000 Slam Dunk Contest win and estimated that his vertical leap was about 37.6 inches. see Measuring Vertical Leap at a NBA Slam Dunk Contest

The above story was picked up by Patrick at givemetherock.com, who said "I would love to see how other dunks measure up".

The original plan for last weeks article was to use video of Michael Jordan's dunk from the free throw line in his 1987 Slam Dunk contest win. However Carter's dunk from 2000 gave us a better example. To measure the vertical leap from broadcast footage of the slam dunk contest we needed one view and image from the video that contained 4 elements. 1. A full view of the player, 2. a view of the underside of the backboard, 3. the basketball rim and 4. the floor below the backboard. All 4 of these features need to be in the image.

GiveMeTheRock.com want to see how other dunks measure up so I went back to YouTube to try and find better footage of Jordan in 1987.

Although the dunk from the free throw line is iconic, it may not be the dunk in which Jordan obtained his maximum vertical leap, because for this dunk he needed to cover the distance from the free throw line to the basket and therefore height was less important. During the same slam dunk contest though, Jordan completes a sideways dunk which scores him a perfect score of 50.

This dunk required Jordan to get higher to complete, so lets use this one to compare his vertical leap to Vince Carter's 37.6 inch leap in 2000.

Here is the video. Jordan's sideways dunk can be seen at about 1:59 for his highest point and the dunk from the free throw line can be seen later on.

Assuming his highest point is at 1:59 in the video, we take a snap shot and then use our known measurements. This time we do not need to use the width of the backboard because we have a side on view that allows us to measure the distance from the rim to the ground:

Height of the rim is 120 inches above the ground.
Michael Jordan is listed at 6 foot 6 inches or 78 inches.
Hip height of a standard man is approximately 53% of his total height. Therefore Jordan's hip height is about 41.3 inches.

These measures are ideal for making a comparison between Carter's vertical leap and Jordan's. The fact that they are of the same height, 6 foot 6 inches, allows us to ignore any height advantage. As an example Nate Robinson needs to have a higher vertical leap than Dwight Howard to make a dunk, for the simple reason that he is much shorter. In our comparison both players are the same height and therefore they both require the same vertical leap to make the dunk. In a slam dunk contest it is not only about making the dunk and this is why we are interested in comparing their vertical leaps during the dunk.

Lets look at the image at 1:59 and the measures we can make.

Because it is difficult to make out the backboard we chose to use the height of the rim above the floor for our scale measure. We know this height is 10 feet or 120 inches. We draw the blue line down from the rim to the floor and give it the scale we desire 120 inches.

Now we can measure how high Jordan's hips are above the ground. This measure at 83.88 inches (yellow line). Subtract Jordan's standing hip height of 41.3 inches from this measure of his hip height at the top of the dunk and we get an amazing 42.6 inches or 6 inches (half a foot) higher than Carter's hip height in the 2000 slam dunk contest.

Of course the different angles of the cameras and footage and the differences in how the vertical leap measurements were made (not using the backboard for scaling in this image but using it for Vince Carter's dunk) means that inaccuracies will still exist. However a quick look through the literature and some past studies of Jordan at his best suggest that he could regularly jump 42 inches during a one handed dunk.

We will therefore assume our measure of Jordan's 1987 dunk to be a good estimate and based on the 2000 video footage of Carter's dunk we will assume that our measure of 37.6 inches is a good estimate of vertical leap for his dunk.

There is no doubt then that Jordan wins this video analysis of sports dunk off. Anyone think they have footage of a dunk with a vertical leap that can top Jordan's?

Measuring Vertical Leap at a NBA Slam Dunk Contest

2010-08-16T15:59:00.000-07:00

The Slam Dunk contest at the NBA All Star event is usually spectacular. Dwight Howard flying with his Superman cape is a great highlight. Slam dunks are all about getting up high and we want to know how high they jump?

Recently a reader of this website asked whether he could measure the vertical leap of winners of past slam dunk contests from NBA footage of the event, including Michael Jordan's leap from the free throw line in 1987. Unfortunately in a basketball broadcast the camera and usually cameras are often moving, panning or zooming to catch the best view of the player, particularly during a dunk. Analyzing the vertical leap from this footage can be tricky.

The answer to the readers question depends a lot on the video footage that is analyzed, but here are a few basics of video analysis and some ideas of how the vertical leap height may be measured from the footage.

Camera angle and view needs to be good to make useful measures of heights (see Video Analysis 101 ). Most footage of the slam dunk contests used multiple cameras and they were often zoomed in at just the wrong time, making this difficult.
We only need one image of the player at the peak of his jump to measure vertical leap, but we will also require some scaling so that we can convert the pixels in the image into a real measurement of height. To do this we need to have a single image that includes the player, the bottom of the backboard, the rim and the floor directly underneath the backboard. With all these in one frame of the footage we can make a measure.
We will also want to know the height of the player so that we can use this height to estimate their vertical leap. We will measure the height of the jump and subtract the players standing height to get a measure of their jump.
Even if all the information is available to us to make the measure, it will still be an estimate as the camera angle may be slightly off and this will make our measure less accurate.

Would this method in fact work? We can try to analyze a slam dunk contest from 2000 and Vince Carter winning with some serious air. Check out the video below:

From this video we can grab a snapshot of the action at 1:44 in the video and do some measures. First we needed to know some standard basketball measures.

Width of the backboard is 72 inches
Height of the bottom of the backboard is 114 inches above the ground
Vince Carter is listed at 6 foot 6 inches or 78 inches
Hip height of a standard man is approximately 53% of his total height. Therefore Carter's hip height is about 41.3 inches.

Now we can make some measures of Carters vertical leap height. This footage has a graphic that measures his jump height at 37 inches. We will use this as a measure to see how well we can do at measuring the jump height using our estimates and video analysis. See the image below:

In the image we can see the following measures:

We know that the width of the backboard is 72 inches. We have drawn a green line along the bottom margin of the backboard and used this known distance to scale all our other measures.
Next we used the blue line to draw a vertical from the bottom of the backboard to the ground. We know this should be 114 inches. Unfortunately as our scale comes from the width of the back board (green line) we couldn't get it to measure exactly 114 inches with our estimates, but we are close at 114.19 inches.
Finally we measure Vince Carter's hip height at the top of his jump and with the yellow line. Here we needed the line to go from the floor at the same height as the blue line to Carters hips. We estimate his hip height at 78.9 inches or 6.575 feet which is almost his head height.
We can also notice that the camera is not perfectly horizontal with the backboard. We can see that the backboard is not perfectly horizontal accross the screen, although it is close. This angle may reduce the accuracy of our other measures.

Finally we can estimate Carter's maximum vertical leap from this video footage and for this particular dunk. We know his standing hip height is estimated at 41.3 inches and we estimated his hip height at the peak of the jump for the dunk at 78.9 inches. We subtract the standing hip height from the jump height and we get 37.6 inches.

If the measure shown during the broadcast at 37 inches is accurate then our estimate is pretty good and we can probably try to do the same measures on other broadcast footage of slam dunk contests. All we need is one image with a view of the backboard, the player and the floor below the backboard as well as knowledge of the dimensions of the basketball backboard and height of the player.

We are always interested to hear about your video analysis projects or hear your comments. We are also available to consult to all our readers on their video analysis and biomechanics needs.

Does Kicking Help to Paddle Faster in Surfing?

2010-07-28T09:08:00.000-07:00

The world best surfer, Kelly Slater, whips around and starts paddling hard into a double overhead wave at Pipeline on the north shore of Oahu, Hawaii. His arms stroke deep into the water right next to the side of his board as he produces the speed needed to catch the fast moving wave beneath him. With another look at some video we also notice that he is kicking hard with his legs.

Getting up to speed

To catch a wave, a surfer needs to paddle the board fast enough to create the forward momentum that will ensure the wave carries the board and rider along with it and does not leave the surfer behind. The surfer must overcome the forces of inertia and gravity and match the speed of the wave as closely as possible. Large waves travel faster and therefore the board speed needs to be faster to catch these waves than to catch smaller waves.

A surfer increases his paddling speed by taking deep paddling strokes with arms close to the board and fingers together. This seems intuitive, but what about kicking hard? Does it really help to kick hard when paddling into a wave?

Slater kicks

In this video of Slater at the 2008 Pipeline Masters, watch how he paddles and kicks for every wave. From this video it is obvious that Slater kicks his legs when paddling into a large wave.

Why do surfers kick?

Kicking while paddling a surfboard has been carried over from freestyle swimming. A freestyle swimmer kicks:

To keep their bodies and legs floating high up in the water. This ensures the body maintains a straight line in the water, reducing drag.
To assist with body rotation and breathing. Breathing in freestyle swimming is timed with the kick.
Swimmers are taught to kick from the hips with slightly bent knees and an extended foot. Kicking from the hips produces the power which can translate into extra speed.
To increase swimming speed. Swimmers use a higher kick count to speed up in the water.

This may work for a freestyle swimmer, but a surfer may not get all the benefits listed above.

A surfer is lying on his board and is being kept afloat by the board itself, therefore kicking is not needed to stay afloat or to support the hips and legs.
Once again as the surfer is on his board with his head and chest up, he does not need to use a kick for breathing and he will certainly not want to rotate his body too much as that may destabilize him on the board.
On almost any surfboard that can be stood up on, the surfers hips will be pinned to the board while paddling and only his feet and knees will be in the water (depending on the length of the board). It is very difficult to kick from the hips while paddling a surfboard and therefore difficult to create the same kicking power as a freestyle swimmer.

Therefore the only advantage to kicking while paddling a surfboard may be to increase paddling speed.

Kicking increases paddling speed

A 2010 study done at Griffith University in the surfing Mecca of Queensland, Australia - Loveless, D., Minahan, C. (2010). Two reliable protocols for assessing maximal-paddling performance in surfboard riders, Journal of Sports Sciences (in press), suggests that kicking while paddling gives the surfer a 9.2% increase in paddling speed over paddling with arms alone.

The study looked at eleven young competitive male surfers and tested them in a field test in a 25m pool. The participants were asked to paddle as hard as they could for 10 seconds. Their paddling speed was measured with a tether like device which was connected to their waste and pulled a cable attached to a spool. The spool contained holes 1cm apart and an infrared light measuring sensor recorded the speed at each interval that the light could pass through the holes. The faster the spool spins the faster the surfer is paddling.

Over this 10 second interval the surfers averaged 1.73 meters per second when paddling with arms alone and 1.89 meters per second when paddling with their arms and kicking hard too. A 9.2% improvement.

So kicking increases paddling speed and Kelly Slater kicks so it must be good.

Surfers don't paddle into a wave for 10 seconds.

If you surf you will know that most of the paddling you do is out to the line up or to get into position for a wave. The sudden burst of paddling to actually catch the wave is likely to last at most 2 or 3 seconds.

From the Griffith University study we can see that kicking while paddling adds speed and allows the surfer to cover more distance (0.8m-1.6m) over a 5 or 10 second period. This will definitely help a surfer get into position for a wave or win a paddle battle for priority during a surfing competition, but does it help a surfer when paddling to match the speed of a wave?

If we go back and analyze the video above we can see that Slater paddles and kicks to get into each of his waves for at most 2 seconds. Theses first 2 seconds of paddling from a resting position are used to get up to maximum paddling speed (this can be seen in the Griffith University study graph on page 54) and therefore the surfer does not get the same 9.2% benefit that he would get over a prolonged 10 second paddle. The advantage will be less and will depend on how much more acceleration can be gained by kicking.

The average advantage of kicking over a 10 second period therefore cannot be used as proof that kicking while paddling will help a surfer catch a fast moving wave.

To kick or not to kick

Unfortunately the Griffith University study does not compare the acceleration that can be gained by kicking while paddling but we can assume that there is an advantage here. Even if it takes the same amount of time, say 2 seconds, to reach maximum paddling speed with kicking and without, the fact that the maximum paddling speed with kicking is higher suggests that the acceleration with kicking will be greater. In other words a surfer kicking will get to a higher paddling speed in the same amount of time than a surfer that uses his arms only. And a higher paddling speed is better for catching larger waves.

The study and physics suggest that if a surfer can kick hard while paddling he will gain an advantage however small it may be. Of course if the kicking destabilizes the surfer on the board or disturbs their arm paddling rhythm then it may in fact reduce paddling speed and make it hard to catch the wave.

The size of the board is also a relevant factor in deciding whether to kick. A good kick can only be maintained on a shorter board where the surfers knees are in the water and not on top of the board. The surfer is already restricted in kicking from his hips as they lie on the board, if the board was also under his knees he would be forced to kick the surface of the water and create turbulence behind him rather than using his feet as paddles just beneath the surface of the water.

If you are a surfer and have a video camera, get into a pool with your surfboard and line up your camera on the side of the pool. Do not push off the pool wall, but paddle straight from a still start for a measured distance say 10 feet or 5 meters, using your arms only and then using your arms and kicking too. Measure and compare the time it took to cover the distance and the speed attained at the end of the distance using a basic video analysis software and see whether kicking to catch a wave would work for you. Let us know what you find out.

The Rules of Sprinting in the Tour de France

2010-07-22T12:11:00.000-07:00

The 2010 edition of the Tour de France is approaching its conclusion in Paris. The race for the yellow jersey, or winner of the Tour, has been an exciting one. Alberto Contador and Andy Schleck have been the stand out riders in the mountain stages. The two are seperated by a small margin of only 8 second, which Contador gained because of a mechanical failure at a critical moment for Schleck.

Stage 18 of the race should put the focus back onto the sprinters, at least those that made it through the mountain stages. The stage sprint winner will rely on skilled lead out riding from their team mates and powerful sprinting to gain the victory. The 2010 Tour has seen dangerous and sometimes illegal moves in the sprints. Mark Renshaw, of team HTC Columbia, was disqualified for head butting another sprinter (not once but three times) as he lead out and created a sprinting lane for his team mate Mark Cavendish.

The sprints seem so chaotic that we wonder how anyone can get through without some illegal moves. The video below describes the cycling rules for sprinting and shows some examples of what is allowed and what can and should lead to disqualification.

How The Race Was Won - Rules of the Group Sprint from Cosmo Catalano on Vimeo.

So now we know the rules.

Two more sprints will be contested in the 2010 tour and we can look out for the way in which the sprinters and their lead out men ride their lanes and deviate from them to cut off opposing team riders.

Mark Cavendish is once again favored. With his speed and power he does not need his team mates to head butt other riders to get another win and without his lead out rider Renshaw, he will get his chance to show us.

Credit the Goalkeepers in the World Cup Final

2010-07-14T14:54:00.000-07:00

Goalkeepers in soccer have a thankless job. They can make all the right moves, make the save and still not get praise for their actions. The striker gets all the credit or rather criticism if he misses.

As I read the post mortem of the 2010 FIFA World Cup Soccer Final between Spain and the Netherlands and won by Spain, I noted that two opportunities(one for each of Netherlands and Spain) were described as bad misses by the striker, with little mention of any goalkeeping skills.

I believe we can give both goalkeepers in this game, Iker Casillas of Spain and Maarten Stekelenburg of Netherlands, credit for excellent performances and two great saves of a very similar type.

Take a look at the two saves. The first is Casillas saving a one on one chance for Arjen Robben of the Netherlands:

This second video is of Stekelenburg saving a shot from Cesc Fabregas of Spain.

Most of us expected the strikers, especially Robben, to score from that position, but in both cases the goalkeepers read the situation and made the best decisions to give themselves a chance of making the saves.

Lets look at what they did to make the shot as difficult as possible for the strikers.

They both come out toward the striker cutting down the angle for the shot. This makes it more difficult for the strikers to simply shoot directly at goal. They now have to be more accurate, go for the corners, attempt to chip over the goalkeepers or dribble around them first.
At the same time as they cut down on the angle both goalkeepers stay upright and balanced, waiting for the striker to decide which way to go. As Fabregas was not directly in front of goal, Stekelenburg also covers a little to Fabregas' right side and thereby cutting off any chance that he may cut back inside.
Both goalkeepers stay on their feet as long as possible, only picking a direction to dive at the last moment. This allowed them to make a better prediction of which way to dive.
In both saves the goalkeepers dive the wrong way. They attempt to predict which way to dive wait as long as possible and consider the tendencies of the striker approaching them before making up their minds. Robben strongly favors his left foot and running at pace it is easier and more accurate to aim across goal, so Casillas chose to dive left and cover the cross goal shot. Stekelenburg was also facing a left footed striker in Fabregas, but as Fabregas was not directly in front of goal and Stekelenburg was already covering his own left side, he predicted that Fabregas would shoot to the inside right corner and therefore chose to dive right and cover this shot.
Both strikers choose the more difficult shot (Robben, inside out, to the bottom right corner and Fabregas across goal to bottom left), and the goalkeepers do a good job spreading out with their legs and getting a little bit of luck to deflect the ball behind.

Both of these are great saves and worthy of a little credit even if some luck is involved. A goalkeeper can only make the best choices to make the strike difficult and then hope for a save.

Of course had either or both of Robben and Fabregas scored, no one would have blamed the goalkeepers.

Well done to Spain the 2010 FIFA World Cup Champions and South Africa for being incredible host. We are looking forward to Brazil in 2014 already.

Lebron Will Pick Complementary Team Mates

2010-07-08T13:06:00.000-07:00

Lebron James' Thursday night "Decision" ESPN special, has created crazy reactions from NBA fans and even normally disinterested bystanders alike. During the special, Lebron will announce the NBA team he has chosen to join or stay with, in his quest for an NBA Championship title.

Where will Lebron play the next 5 odd years? Reports suggest his decision is made and he will join Bosh and Wade in Miami, but we won't speculate or add to the confusion.

We know why Lebron can command such attention, he is a phenomenal athlete and basketball player. Along with Dwayne Wade and Kobe Bryant, he stands as the best of the NBA. There is little doubt that he will make any team he plays on a championship contender.

In Cleveland Lebron has contended for a number of years now, but has still not held the Larry O'Brien trophy. Whichever team he chooses, he will want team mates that complement his game by being skilled where Lebron is weak.

Lebron has very few weaknesses, but one possible weakness is his jump shot. Of course with some hard work it will improve, but if Lebron joins a team with an excellent outside shooter, he will be able to achieve quicker than if he tries to do it all himself. A dangerous skilled offensive partner will also give him more space on the floor as defenders will need to cover another great player.

So Lebron has studied the video and knows which team mates will work best for him. We expect him to join the likes of D-Wade or Derrick Rose in Chicago and benefit from their strengths.

Here is James vs Wade during the 2010 NBA season. The evidence suggests a strong partnership with every possibility of a championship.

Predicting the Direction of a Penalty Kick

2010-06-28T16:24:00.000-07:00

The 2010 FIFA World Cup is producing some exciting football. As we move through the knock out rounds and a winner must be decided for each game, the possibility of penalties for a game that ends in a draw becomes very likely.

ESPN's Sports Science program recently did a comparison between baseball hitting and the possibility of a goalkeeper saving a penalty kick. The presenter, John Brenkus, concludes that it is more difficult for a goalkeeper to make a save than for a batter to get a hit. The overall batting average for 2009 was .258 or 25.8%, while the annual save rate for penalty kicks is around 22%. Watch the Sports Science clip here.

Although it does seem almost impossible to make a penalty save, goalkeepers may be doing as well as they are because they are reading the kickers body language before deciding which way to dive.

A recent study by Gabriel J. Diaz of Rensselaer Polytechnic Institute, used motion capture technology in an attempt to determine clear indicators for the goalkeeper, that would help them to guess the direction the ball will be kicked from the penalty spot. This may suggest why goalkeepers guess the correct direction about 57% of the time (as suggested in the Sports Science clip), rather than only 50% of the time.

In his study, Diaz identified five reliable indicators of the direction the ball will be kicked. He discovered that four of five of these indicators were used by people (not goalkeepers) he tested that were able to identify the direction the ball would go before it was kicked. Read more here.

Two of these indicators are the angle of the hips as the kicking foot swings through and the angle of the support foot on the ground prior to kicking. These two indicators are known to football coaches and may already be used by goalkeepers.The other three indicators are "distributed movements", co-ordinated movements that balance the body, and have not been discussed by coaches or soccer players previously.

The idea that motion capture and or video analysis can be used to improve performance is not new to any of us here. Diaz rightly suggests that these predictors, including the distributed movements, could be pointed out to a goalkeeper and possibly give them an advantage. They would still need to be able to process these indicators and make a quick enough decision to gain an advantage and that may not be so easy.

Some great 2010 World Cup quarterfinal match ups are coming together. Argentina v. Germany and Brazil v. Netherlands should be some high tension and hopefully highly skilled encounters. We hope there are no penalty shootouts. But if there are, try and pick out the direction the kicker will go by watching his hips and standing leg and any other movements you think give it away. If you are a goalkeeper, let us know how you guess direction of the penalty kick.

Sympathy for the Referee

2010-06-21T14:24:00.000-07:00

The last week has seen numerous bad refereeing decisions in both the World Cup Soccer and the NBA finals. As the NBA finals are won and done (Lakers in 7) and in basketball, a 7 game series means that the bad decisions tend to even out over its course, let's turn our attention the the FIFA World Cup.

In soccer bad refereeing decisions are etched into every fans memory.
Quickly, what is the most famous FIFA World Cup goal? The first goal that comes to mind is Maradona's "Hand of God" goal in the 1986 quarter-final win over England. A goal that should not and would not have been awarded, had the referee seen Maradona's fist punching the ball into the net.

The 2010 FIFA World Cup is trending along a similar line. Siphiwe Tshabalala's spectacular opening strike of the World Cup for South Africa or David Villa's excellent skill to get Spain going, should be among the most memorable goals, but most of us are still talking about and replaying the goal by USA's Maurice Edu, which was disallowed by Mali referee Koman Coulibaly for an unknown reason.

Before damning the referees to a far less stressful existence in their day jobs, we may consider the difficulty they have controlling the game, making correct calls every time and what these controversies mean to soccer in general.

Difficult decisions are part of the referees job. We have previously written about the difficulty of getting into the correct position to see all that goes on in a soccer game. Even with TV we often don't see what happened until we get the instant replay from 3 different angles. Sometimes, even then, we are still not sure.

The referee needs to make his decisions quickly. Sure he can get some help from his assistant referees, but decisions also need to be prompt so that the game can continue to flow and be entertaining for the spectators. Player skill, speed, aggressiveness and even simulation, sometimes diving with theatrical eloquence to win free kicks and penalties, make it even harder.

In the USA vs Slovenia game on June 18, 2010, the referee was attempting to keep track of at least 3 different tussles between the players in the penalty box. In most cases, to those of us who got to see it more than once and from more than one angle, it looked obvious that the Slovenia players were fouling the Americans and that a penalty should have been awarded to the USA. The referee however had one view and one chance to see all that was happening and made his call.

Of course we hear the argument that the referee should simply have explained the call. Perhaps he should have, but would that really have appeased the United States players, coach or fans? After all, the goal was still disallowed and video replay is not currently used in soccer to overturn or review a refereeing decision.

This leads me to the other benefit of a poor decision - Interest in the game. The USA is not normally a country to be gripped by soccer fever, but the excitement for the deciding group game against Algeria has been raised a few levels because of the refereeing error. Americans who usually label soccer boring will be tuning in to see if their team can win and qualify for the round of 16, despite the terrible judgement that has befallen their team.

A similar enhancement of the game can be seen around the world. Every game England plays against Argentina, whether Maradona is Argentina's coach or not, is at an elevated level because the the "Hand of God" goal. The next time the Republic of Ireland play France, Irish revenge will be on everyones mind because Thierry Henry used his hand to assist in a goal for France over Ireland to qualify for the 2010 FIFA World Cup. The list goes on, everyone creating renewed interest, excitement and rivalries.

Let's have some sympathy for the referee. After all they are only human and can make human errors. And we so enjoy the rivalries they may have created by disallowing or allowing a goal here and there.

OK with sympathy we can now try to understand what Mali referee, Koman Coulibaly saw in this goal to disallow it. Could this video have the answer?

The Unpredictable World Cup Soccer Ball "Jabulani"

2010-06-07T14:58:00.000-07:00

Can you feel it? The FIFA World Cup Soccer Finals produce an electricity unmatched by any other world sporting event with only the Summer Olympic Games being in contention.

To add to the excitement every 4 years since 1970, FIFA has introduced a new soccer ball for the World Cup tournament. As the World Cup nears the opening game on June 11, 2010, we once again hear the anguished cries of the forsaken goalkeepers in reference to this years Adidas "Jabulani" ball.

Every 4 years goalkeepers complain that the new balls flight path is more unpredictable. “Highly unpredictable when hit from long distances.” says Wendell, the Brazilian goalkeeper coach about the "Jabulani" ball. In 2006 England's goalkeeper Paul Robinson criticised the then World Cup Ball named "Teamgeist" for being too light and behaving unpredictably.
Sound familiar?

The "Jabulani" ball to be used at the World Cup hosted in South Africa, is made with 8 3D molded panels. This is fewer than the 2006 ball, made with 12 panels and of course far less than the original soccer ball made with numerous black and white panels that were stitched together. The "Jabulani" also has aero grooves, which are there to stabilize flight in the air and will provide grip in the wet for both strikers and goalkeepers. The ball is also said to be rounder than any previous soccer ball because of the 3D molded panels.

Time to use our video analysis to see what the fuss is all about. Take a look at a recent goal scored from a free kick by China's Deng Zhuoxiang against France on June 4th 2010.

Those of us who have watched football and particularly free kicks in the past will have seen this type of thing before. Watch as the ball moves toward the goalkeepers left at the start of the flight and then swerves right after passing the wall.

The French goalkeeper Lloris moves left to cover the shot and then has to change direction to his right as the ball swerves past him. Great free kick, whether Deng intended it or not.

Now take a look at a goal by Danny Rose of Tottenham Hotspurs against Arsenal in February 2010.

This goal is scored with the old "Teamgeist" ball and the movement through the air can be considered as dramatic as that for Deng's goal.

The goalkeepers might not like it very much but each time a new ball is created it does improve the control that the strikers have over the ball.

The top spin that Nadal uses to destroy opponents in tennis, the curve ball thrown in baseball and the reverse swing in cricket are all examples of so called "unpredictable" behaviour of a round ball. The fact is that with a more better ball, a player that can create enough speed and spin in a specific direction, can use physics to make the soccer ball move around "unpredictably" for the goalkeeper.

To measure the movement on a perfect round ball lets assume that a free kick is taken 30 meters out and hit at a good 30 meters per second or around 70 mph with a spin of about 10 revolutions per second. With this information and knowledge of the balls coefficient of drag we could calculate the distance the ball would "move" swerve off course at about 4 meters or 12 feet, which would be more than enough to beat a goalkeeper.

This coefficient of drag is what is being altered by the new ball. The fewer panels, rounder shape and aero grooves all have an effect. The fewer panels and rounder ball allow the striker to get more of the ball in his shot and also control the rotation on the ball. This should result in higher ball speeds off the players boot and cut the initial drag. The increased rotation creates the effect of moving air on one side of the ball faster than on the other, creating a force which makes the ball swerve more. The aero grooves produce turbulent flow around the ball (similar to the grooves on a golf ball) allowing it to also cut down on drag and fly through the air faster and further.

The extra movement on the ball occurs as the ball slows down and the drag forces take effect. The higher the ball speed and spin initially the more these drag forces can pull on the ball as it slows down. The design of the new ball has allowed us to use physics to better determine what will happen to it. The multi-paneled soccer balls of the past were far more unpredictable because of the seams, stitching and shape which affected its flight and movement.

To simplify all that, the "Jabulani" ball gives the strikers more control than they have ever had before and the ball flies faster through the air, making movement of the ball more dramatic off a well hit shot. The striker still needs to have control and power and be capable of imparting them to the ball in a perfect sequence to have the desired "unpredictable" effect.

Goalkeepers will learn to adjust to the new flight and speed of the "Jabulani" ball and then we can wait in anticipation for World Cup Finals Brazil 2014 to hear the new complaints about the "unpredictable" new ball.

In the meantime we will enjoy watching some spectacular goals and watch out for video that we can analyze that might show how the strike made the ball move like that.

Go Bafana Bafana and USA soccer.
Laduma! (Goal !)

"Perfect" reason for expanding replay in MLB

2010-06-03T10:49:00.000-07:00

Baseball purists have successfully delayed the use of video replay technology for a very long time. Arguing that the tradition of making all calls visually by the field umpires is the only way to go, a seemingly increasing number of blown calls have pressured the MLB to begin adopting video replay to help minimize inherent human errors.

In 2008, the MLB begin using video reply for the following calls:
Home run calls (fair or foul)
Whether the ball actually left the playing field
Whether the ball was subject to spectator interference

This obviously doesn't cover every single call, but there is a point of diminishing return on the use of replay. However, there are still some more calls that we think warrant the use of the technology. On June 2, 2010, Armando Galarraga pitched what should have been called a perfect game for the Detroit Tigers. However, on what appeared to be the last out, the umpire called the runner safe at first base. Even the runner and his teammates thought the game was over. Replays from every available angle clearly show the defensive player had his foot on first base and the ball in his glove well before the runner reached the base. So instead of having the third perfect game thrown in 2010 (and only the 21st EVER), Galarraga continued to pitch until the final out was made.

As you may well know, baseball fans are obsessed with statistics and records. So we'd have to believe even the most traditional fans think it's a shame that such a brilliant performance be left from the record books due to a blown call. Certain calls are meant to be subjective, such as strikes and balls; and it's an enjoyable part of the game to watch how the players must make minor adjustments based on who's behind the plate that day. But other calls should be black and white (i.e., a player either reaches a base safely, or is out), and these are the types of calls that should subject to video replay.

On a somewhat unrelated note, Galarraga handled the situation like a champ. He just grinned at the bad call, and went right back to work, pitching the remainder of a shutout. Many other players would've acted like a two year old and thrown a tantrum; many others would've lost the mental focus required to perform at a high level. So hats off to you, Armando - not only for a terrific pitching performance, but for simply respecting an umpire's (incorrect) call, and showing some real class.

Sharing Sports Video Analysis

2010-06-02T16:49:00.000-07:00

On the Video Analysis of Sports site we often show you some analysis that we have done using a particular software. We have used software from Dartfish, Innovision Systems Inc. - MaxTRAQ and our favorite open source application Kinovea.

Recently we were introduced to David Keefe. David let us in on his new project called UpMyGame. You may have noticed UpMyGame as a new menu item on this website. We do not endorse one video analysis software product over another. If you read our posts regularly you will know that we believe the most important aspect of video analysis for sports is camera positioning and quality of the video footage captured. Features of a video analysis software such as drawing lines, calculating angles, scaling and measuring distance and synchronizing two videos are great to have and can be found in many applications.Therefore we like video analysis software that is easy to use, easy to share and of course as inexpensive as possible.

So why do we have a link to UpMyGame on our website? Easy to use, easy to share and free for a start, but what we really liked about UpMyGame is that it is hosted online and your videos can be analyzed, commented on and shared online by you, your coach or players or anyone you allow to view it.

The software allows you to create coaching session for players or teams and can be hosted or embedded directly into your own website. This embedding feature is one of our favorites as it allows us to do some analysis and very simply share it with you on this website.

Below is an embedded coaching session using UpMyGame. You may have seen part of this analysis before at Improving Your Basketball Free Throw with Video

The UpMyGame software allows us to measure angles, draw lines, highlight areas of interest and make comments. The audio comment tool seems particularly useful for coaches to share their views and explain their analysis in more detail.

For the athlete who is trying to get more information there is also the option to ask for coaching. UpMyGame has a simple button to "Request Coaching" which allows you to ask a coach or UpMyGame member to have a look at your video and do some analysis. The coach has the opportunity here to charge for any coaching requested or if he feels generous he may just offer to help for free.

If you are looking for some video analysis software to analyze your sports performance or that of your athletes then we suggest that you have a look at UpMyGame. The free sign up price is hard to beat and if you ask for coaching from us "Sadaka" we may make you famous as we can write about and embed (with your permission) your coaching analysis directly in one of our future posts.

Top Spin Wins for Nadal at the French Open

2010-05-27T10:56:00.000-07:00

Rafael Nadal has won the French Open Tennis tournament four times. He owes many of these wins to his exceptional top spin forehand. As he goes for his fifth title in 2010, we thought it would be interesting to analyze some video and describe why top spin wins on clay.

Tennis balls loose much of their speed when they bounce on clay tennis courts. This means that the powerfully hit flat shots that Roger Federer uses to destroy opponents on hard courts and grass lose much of their speed on clay. The ball also tends to bounce higher on clay. The flat forehand that normally stays low to the ground slows down and bounces higher, allowing the opponent to hit it back with interest.

Top spin is the effect on the tennis ball created when it rotates in the same direction that it is travelling. Top spin shots are ideal for clay:

Top spin shots can be hit higher over the net and deeper into the court. This is because the top spin makes the ball drop quickly with a downward force known as the Magnus Effect. The deeper you can push your opponent on a clay court the harder it is for them to play an offensive shot in return.
Top spin ensures that the ball bounces higher too. The top spin bounce along with the extra high bounce on clay results in a return shot that is hit at shoulder height or above making it much more difficult to return with power, especially with a one handed backhand like Federer's.
Top spin also creates a heaviness in the shot. As the ball is spinning toward your opponent and in the same direction as it travels, a well hit top spin shot will come onto the racket faster after the bounce. This is more evident when the shot is used on hard courts, but Nadal is powerful enough and creates sufficient top spin to have players comment on this aspect of his shot even on clay.

So now that we know what makes top spin effective on the clay at Roland Garros, lets take a look at Nadal's top spin forehand in slow motion in the video below.

Nadal imparts top spin on the ball by swing his racket from a low position to a high position, using the racket to skim over the ball and creating a rotation in the same direction as he is hitting.

As you watch the video notice how Nadal uses all his big body parts, hips, torso and shoulders to create the power in the shot and then uses the arm and racket to create the top spin and direction.

He starts by rotating his hips, torso and shoulders away from the ball as he brings his racket back to a low starting position.
He positions his feet and then starts by rotating his hips first, followed by his chest and shoulders toward the direction he plans to hit, using the kinematic sequence to create racket speed.
Now he can swing his arm and racket through the ball, using the power that was created by his body and the control created by his arm and wrist.
He swings the racket low to high, sliding the racket over the ball during the shot. Some call this a windshield wiper action. This action creates the top spin.
Nadal ends with the racket at shoulder height and over his right shoulder. Depending on the shot he sometimes follows through with the racket even higher than this.

Knowing why Nadals top spin forehand is so effective on clay and how he hits it is one thing, offering effective counter to such a shot is something else. Another French Open final between Nadal and Federer would be a great test of Nadals top spin and clay court skills versus Federer's creative and adaptive style. In previous years Nadal's top spin has won out, but Federer has 16 Grand Slams and is playing better than ever.

Free Running - Just Watch!

2010-05-20T17:55:00.000-07:00

Like many others, I used to think a lot of the "extreme" stunts shown in soda commercials were faked using sophisticated video editing software. However, I recently found out many of them are actually performed by athletes engaged in an activity called "free running" (sometimes called "parkour"). Besides perhaps a decent pair of athletic shoes, no other equipment is needed, as participants use their natural or man-made surroundings as obstacles with which they interact by jumping, scaling, and running on, around, over, and under.

Unlike a gymnastics competition, participants aren't required to stick and hold a landing. It's not actually meant to be a competition against others anyway; it's meant to be a way for individuals to express themselves. And because the athletes are often going from one obstacle to another, it wouldn't make sense to hold the landing anyway.

Please enjoy the following video, and for goodness sake, don't try most of these stunts!

Usain Bolt: Room for Improvement

2010-05-18T09:47:00.000-07:00

We have previously stated here that we think Usain Bolt can lower the 100 meter world record.

We have suggested that he can start faster, train harder on his fitness and of course refrain from celebrating before crossing the line. All of which suggests that his 9.58 second 100 m and 19.19 second 200 m world records will be broken.

On Saturday the BBC aired a documentary on Usain Bolt "Usain Bolt: The Fastest Man Who Has Ever Lived". In this documentary Michael Johnson, the 400m world record holder and second fastest man over 200m (after Bolt) talks about the biomechanics of Bolts sprinting.

Johnson says of Bolt: "He has ... an incredibly long stride combined with the ability to execute a race like a shorter sprinter - generating the same explosive power. That combination makes him so much faster than the rest of the field."

But he suggests that slow motion video shows that bolt has lateral movement in his sprinting mechanics. In other words he moves his body side to side as he runs. This sideways movement reduces his forward power by wasting energy in keeping his balance. If Bolt were to remain still with his upper body as all good sprinter should, he may be able to propel himself even faster.

Of course the lateral body movement may be a result of other inefficiencies with Bolts mechanics. It is possible that he turns his knees or feet out a little. As Michael Johnson is an excellent proponent of running mechanics and a highly qualified coach, we are sure that he and his team setup their cameras in the best way to measure these inefficiencies correctly.

One of the most important aspects of video analysis for sports is to ensure that we get video images that will allow us to do the analysis we want. If we are interested in Bolts side to side sway we need to have a camera directly in front and or behind him as he sprints down the track. We want to be able to measure how much his body moves laterally and see if his knees and feet are out of alignment. With this information we can help our athletes improve their mechanics and speed.

Jason Heyward Practices Perfect Hitting

2010-05-17T12:06:00.000-07:00

Throughout his high school playing career Jason Heyward was always recognized as a prodigious baseball hitting talent. This recognition and the hype that began early in 2010 with his debut in the Major Leagues have proved to be legitimate.

Heyward has lived up to his reputation. He began his professional career by hitting a 3 run, home run on the first at bat of his MLS career for the Atlanta Braves against the Chicago Cubs. He has followed that first strike up with 7 more home runs and a batting average of .276 for the season.

Heyward has started his MLS career this way because throughout his youth league and high school playing career, he has practised perfect hitting mechanics.Below is some video of Heyward hitting at different stages as he advanced in the youth leagues, 2004, 2005 and 2006.

From the video we can see that Heyward from as early as 2004, has been taught and understood how to create power in his hitting by using his large body parts such as the hips, torso and shoulder and combining this with perfect timing.

On this site we call that the Kinematic Sequence. The kinematic sequence can be described in almost any hitting or throwing sport. By rotating the major body parts in sequence the hitter is able to create bat speed. The hitter starts in the wind up position, bat above the head shoulders and hips rotated away from the pitcher. He then begins the kinematic sequence by planting his front foot and unwinding in sequence, first the hips, followed by the torso and shoulders, then arms and finally the bat.

Each subsequent body part rotates quicker than the previous one until in the end the bat has accumulated all the speed from the sequence and can strike the ball with power created from the movement of the whole body and not just the arms, wrists and hands.

Lets break down Jason Hayward's swing and take a look at his mechanics and kinematic sequence.

These first 3 pics show Heyward at the load position in 2004, 2005 and 2006 (left to right). Notice how as he gets bigger and stronger he continues to maintain that loaded position of shoulder and hips facing away from the pitcher. This stance prepares his body like a compressed spring to release all the energy necessary.

As he moves through his swing we see that Heyward takes a step forward and drives with his hips first rotating them to face the pitcher while his shoulders, arms and bat remain behind. His shoulders and arms are beginning to rotate at this stage. By rotating his hips first he is using their rotational speed to increase the speed of his shoulder rotation which will follow.

Just before ball contact Heyward has now rotated his hips and his shoulders and now only the arms and bat need to hit maximum rotation speed. Each large body part has built on the speed of the previous one and thereby increased his bat speed. To get maximum speed he still needs to complete the swing by following through. His bent arms allow him to hit through the ball and follow through to maintain balance and control.

As we look through the video and the images, we notice that Heyward practiced perfect mechanics from as early as 2004 and probably before. His batting coaches made sure he used proper technique throughout his career. From 2004 to 2005 and 2006 and on to his MLB career he has continued to put together his swing using the kinematic sequence of events.

Of course there are other factors in Heywards past and possible future success. His size and strength (6'5", 240lb) are definite bonuses. However a powerful hitter will need to use all his most powerful muscles to have a long and successful and injury free career. In fact Heyward currently has a small groin strain but this is more likely the result of stretching for an outfield play rather than anything to do with his hitting. We hope to see Heyward continue to impress and as long as he maintains the perfectly practised mechanics we expect he will.

Practising perfect mechanics is an important element of training for any sport. It is very difficult for a good young athlete to change his bad habits after practising them for many years. Video analysis can help to pick out these bad habits and correct them at an early stage allowing your athletes and kids to practice good mechanics, avoid injuries and improve faster.

Using Video Analysis for Strategy

2010-05-10T11:57:00.000-07:00

Video analysis can be used to evaluate sports performance and technique. We discuss many of the biomechanics aspects and tools used to do performance assessments right here on this website. Video analysis however can also be used to provide detailed game strategy and analysis of on field play.

We see these game strategy statistics all the time when we watch almost any sport on TV. How many shots did Kobe Bryant take and make. What percentage of first serves did Roger Federer get in and how many resulted in winning points. These statistics are fun for the viewer, but they are essential to the coach and player in refining their strategy.

Let's take an example from basketball, as we are currently watching the NBA playoffs. Any team coming up against the Orlando Magic this year will need to find a way to get past Dwight Howard, who was once again named defensive player of the year. The teams employ a coach or video analysts to watch every play that Howard makes. Every time he blocks a shot or an opponent manages to beat him and score. Using this information they can determine how best to play against him.

Below is video of some of Howard's best blocks of last season. Notice how often Dwight is alone and far away from an opposition player as he gets into position for the block. This may seem necessary in order to make the block, or as the Orlando Magic play a zone defense he may not have a specific man defensive assignment. Coaches or video analysts though would look at this video and may be able to create plays that take advantage of his position on the floor.

Of course a team also needs to play to its strength and similar video analysis of the coaches own team can be used to determine how they may take advantage of any opposition mistakes, close any gaps or change any patterns that may be obvious and strategies the best approach to take on an upcoming game or player.

To do Video Analysis of this sort properly you need to have some basic equipment.

You will definitely need a video camera and to set that camera up so that you can see the whole game. This can be difficult in sports with large fields such as soccer or rugby.
For larger fields you can use 2 video cameras, with each one focused on, one half of the field.
A great advantage in well televised sports is that much of the video footage already exists. A recorded video of an NBA game will allow you to track most of the players on the court for most of the game.
Some video analysis software is also recommended. This software can be the same as the software that you use for performance and technique analysis, but the software must allow you to tag events. Tagging events such as the first serve will allow you to go back and look at all the first serves in one place. This will enable some statistical analysis of the results of the serve and if you have software that allows it you can also analyze each serve for technique and performance.

The website http://www.thevideoanalyst.com/ has some great information on video analysis of this type and everything that you may need.

When working with a team or player combining this type of video analysis with biomechanics and technique analysis will provide excellent resources for performance improvements wherever they are needed.

Crazy backflip dunk!

2010-05-04T10:09:00.000-07:00

In a recent game between the Atlanta Hawks and Milwaukee Bucks, an amazing halftime feat was performed. The Bucks' mascot Bango climbed a 15-20 foot ladder (reports vary), did a backflip off the top step, and dunked a basketball, before falling onto a landing pad. Although the video was taken from a handheld camera, it's definitely something worth watching over and over again. Enjoy!

Analyzing the Details of the NFL Combine

2010-04-28T09:07:00.000-07:00

Every year the NFL scouting combine is attended by all 32 NFL teams, scouts, coaches, trainers and owners. They watch prospective players run 40 yard sprints, bench press, vertical jump, broad jump, 3 cone drill and shuttle run. They are there to get an in depth analysis of the college and invited players who they plan on drafting.

Now that the 2010 NFL draft is completed, with quarterback Sam Bradford going first and defensive tackle Ndamukong Suh going second, how much does the scouting combine affect the results of the draft?

As many of the college football players entering the draft have been in the spotlight for a couple of years at least, most scouts and coaches know what to expect from each player. If the scouts impression of a safety is that he is fast on the field when covering a wide receiver, he is unlikely to change his mind when the player runs only 4.45 in the combines 40 yard dash (a great time would be under 4.4).

Sticking with the 40 yard dash, each football position has a different requirement. A running back, wide receiver or safety may be required to run 40 or even 60 or 80 yards as quickly as possible. The speed at which they cover the ground is what makes them great.

The defensive and offensive linemen on the other hand are expected to have excellent reaction time and acceleration over 5 or maybe 10 yards. They need to hunt down quarterbacks or hold back defensive tackles. Their 40 yard time is almost irrelevant, but their reaction time and acceleration will be critical to their performance on the field.

The trainers watching the combine know what to look for and are using video replay to analyze the athletes' performances in much more detail.

A recent episode of Sports Science did a great job of getting into the analysis of the results of the NFL scouting combine. Below is some video of Ndamukong Suh and some detailed analysis of his 40 yard dash and his tackle force. As a defensive tackle Suh's job is to react quickly, accelerate over a short distance and hit hard. This Sports Science segment does a great job analyzing these specific details.

What is interesting in the video is Suh's reaction time recorded by the Sports Science episode at 0.26 seconds. In an analysis of Usain Bolt, the 100 and 200 meter sprint world record holder, Bolt's reaction time for his world record 100 m was recorded as 0.145 seconds. Of course Bolt is a lean sprinter, using blocks and spikes and Suh is not, so this is not a fair comparison.

However the standardized tests and gathering of all potential recruits on the same day at the same time at the combine, allows trainers and coaches to compare all defensive tackles with the type of detailed analysis seen in the video. Suh's reaction time in comparison to other defensive tackles is what will be relevant, although his 300+ pound frame and tackling power will also be important.

The scouts expect the players they are scouting to perform to spec and very few players can change their draft position with any significance based on excellent performance at the combine. The detailed analysis that we do not see may however determine which team takes which player and how their NFL contracts are negotiated.

How Fast is a NHL Goalie?

2010-04-21T09:47:00.000-07:00

In the NHL, saves win games and never more so than in the playoffs. The NHL goalie's quick reactions can mean the difference between a team advancing to the next round of the Stanley Cup and pulling out their Hawaiian shirts for an early summer.

The shootout is one of the ultimate tests for the goalie. Goalie against shooter, one on one. Shooter tricks vs goalie nerve and reaction speed. Because of this one on one scenario, the shootout is a great way to analyze how fast a goalie reacts.

In the 2009-2010 season, Sidney Crosby of the Pittsburgh Penguins, has been the best shooter in a shootout, scoring 8 of 10 shots. In the goalie stakes, Ilya Bryzgalov of the Phoenix Coyotes has the best record saving 45 of 62 shots for a 72.6% save rate. There are goalies with better saving percentages but Bryzgalov has won the most games (8) with his 45 saves.

Below is some video of the top shootout saves from the 2008/2009 season. What is great about NHL TV coverage is the overhead view of shots on goal. This perspective allows us to easily calculate how quickly a goalie needs to react to make a save in a shootout situation.

To make a calculation of reaction time we will need to know some basic detail about ice hockey and to use some inexpensive or free video analysis software to do the calculations.
The NHL hockey net and goal crease gives us a scaling dimension in the pic below. We know that the goal crease (red block with arc in front of the net) is 8 foot wide and 6 foot from goal line to top of the crease. We can place a grid on top of this goal crease and estimate from this that each block is 6/8 foot wide and 1 foot long.

Now we can look at 2 snap shots of the 2nd save in the video above by Jason LaBarbera.
We have included a time clock along with the grid so we can see how long it takes from shooting the puck until the puck hits the glove and therefore how much time LaBarbera had to react.

We can see that from the moment Schremp makes his move to shoot until the puck is in the glove is 0.5 or half a second. This may be an over-estimation of the time but it will work for our analysis.

With our grid and knowledge of the grid dimensions we can also measure how far the puck traveled over this time. In our first pic we can see the puck is at the bottom corner of the goal crease and in the last pic the puck is in the glove almost on the goal line 0.5 seconds later. The puck therefore traveled 2.5 grid spaces in length and 6 in width or about 2.5 ft in length and 4.5 ft in width. If we use a basic Pythagorean equation we know that the puck traveled about 5.15 feet.

We can calculate that LaBarbera had 0.5 of a second to react to a puck traveling at approximately 10.3 feet per second over a distance of 5.15 feet.

Some video analysis tools make this calculation much easier to do by allowing you to set scaling distances in the video and calculate the distance the puck traveled and even its speed.

The speed of the puck from a slap shot in ice hockey can reach as high as 105 mph, which is 15 times faster than the shot we have just analyzed. However it is not only the speed of the puck that is important for a goalie to make a save. The distance the puck needs to travel and the time available are all important factors. In one on one shootouts it is often the speedy reactions to skilled stick work, that keeps the puck out of the net.

100 Miles and Runnin'

2010-04-19T16:03:00.000-07:00

No, we're not talking about a rap from the early 1990's here; we recently heard about a couple everyday athletes who decided to run 100 miles to the southern California musicfest Coachella, in an effort to raise money for a group called Charity : Water. The goal of the charity is to help impoverished groups have better access to clean drinking water.

Inspired by the book "Born to Run" by Christopher McDougall, two DJ's decided to take this challenge upon themselves. We found this video showing some clips of DJ's Sleeper and Aristocrat scouting out the route.

In an interview I heard a few days ago, DJ Sleeper mentioned he did attempt part of the run through the desert barefoot. For more information on barefoot running, please check out these articles: Running in Minimal Shoes, and Running Barefoot and in Shoes

Although the two runners fell a little short of their goal (they had only run 80 miles by the time they needed to get to the festival to perform), they said they intend to finish the remainder of the route, in the spirit of the charity. We commend these fellows for attempting such a difficult challenge, wish them the best of luck in completing it, and hope the charity succeeds in its goals, as well.

Can Kobe Shoot Without Using his Index Finger?

2010-04-13T17:29:00.000-07:00

The 2010 NBA playoffs are about to begin and the defending champion Lakers look to be a couple of players short of a repeat. The main problem for the Lakers is Kobe Bryant and his dip in shooting form. His shooting has always been his most dangerous weapon and it is not firing now.

Over the last 5 games Kobe has attempted 109 field goals and made only 43 of them averaging just over 39% when his season average is around 45.6%. Kobe suffered, along with other injuries, an avulsion fracture to his right index finger earlier this season. In most games he has managed to continue to shoot reasonably well with this broken finger as can be seen by his season average field goal percentage, but something has changed recently.

Can we blame his finger for his loss in shooting form? Unfortunately we were unable to obtain any video of Kobe that focused on the hand and how he may have changed his grip or the mechanics of his shooting to account for the pain or the cast/bandage on his finger.

But lets take a look at this slow motion video of a basketball free throw and particularly of the hand and fingers at the point of release.

Here is a close up of the hand at point of release. Notice that this recreational player shoots the ball off the fingers of his shooting hand as he should. Our player does not follow through with his wrist correctly, but our focus is on his fingers. We can see that the ball comes off his fingers and that the index finger imparts the last bit of spin and push to the ball. This is expected as the index finger can execute tasks with more control than any of your other fingers, just think which finger you use on your iPhone or iPad to navigate around.

Back to Kobe. It is pretty obvious from the video that the index finger plays an important role in shooting the basketball. But Kobe has had this injury for a while and although it dented his shooting average for a few games in January, it seems to have only recently started affecting him again.

In order to continue to shoot well after the injury in December 2009, Kobe most likely studied his shot on video and made adjustments to the way he executed the final phase of the shot (the ball release). With a cast on the index finger he made and adjustment to keep this finger off the ball and out of the way when shooting and used his middle and ring finger to create the backspin and final push for the shot. He definitely seemed to work it out but he never looked exceptionally fluid with his shooting technique, even when he made the shots.

In the last 5 games something has changed. It is possible that Kobe's finger has healed sufficiently and he is no longer using a splint. The basic wrapping may allow him to use the index finger during shooting once again. The problem may be that the finger is not entirely healed, otherwise it would probably be out of the wrapping altogether. Kobe may be trying to go back to his normal shooting mechanics or simply trying to once again tweak his mechanics to accommodate the new condition of playing with his index finger taped. Either way he will need to find some mechanics that will make him an effective shooter through the play offs as the Lakers will most likely need him to succeed again.

The use of video analysis can assist any athlete in making the necessary adjustments to improve or change mechanics when needed. Of course we do not suggest that you continue to play and change your mechanics if you are injured. Unless you are payed to play, it is better to analyze video and practice to perform correct mechanics that will improve your game and also prevent injury.

Lionel Messi Magic Motion

2010-04-08T10:19:00.000-07:00

After Lionel Messi's destruction of Arsenal in the Champions League Quarterfinal, we found the article below fun to read.
Is the real Lionel Messi better than the virtual one?

While EA sports use motion capture to make their games seem realistic, we can use it to analyze exactly how the real Messi does it. We can watch slow motion replays of each goal and examine how he balances and moves the ball off each foot and creates the space to mesmerize and make even a great team like Arsenal look average.

Progressive Surfing Needs Analysis

2010-04-06T09:33:00.000-07:00

The Surfing World Championship tour is currently in the middle of the second event of the season held at Bell's beach (made famous in the movie Point Break)and by now many surfing fans will know that the judging criteria for 2010 have changed.

If you are a surfer or simply a fan of competitive surfing and the likes of Kelly Slater or Mick Fanning then you will know that the Surfing World Champion is determined by the overall points winner of a 10 event world championship tour.

Each wave in a man on man competition in surfing is scored as the total of points for 2 waves. Each wave is scored out of a maximum of 10 points. Judges now reward progressive and aerial maneuvers with more points. So one extremely progressive, difficult move can potentially score a surfer 10 points if he performs it perfectly, lands it and rides out. Surfing judges use the following criteria to determine the surfer's wave score:

Commitment and degree of difficulty
Innovative and progressive manoeuvres
Combination of major manoeuvres
Variety of manoeuvres
Speed, power and flow

The new judging system obviously wants to see surfers try different and risky tricks and combinations of tricks and will reward them for landing these tricks. Although from our casual observance it seems surfers get some points for trying progressive maneuvers, they definitely get many more points when they punctuate the trick by landing it and flowing back into another move or back into the wave itself.

The video below has some excellent examples of progressive aerial surfing, at Bondi Beach in Sydney, Australia, by some of the Worlds best surfers.

The importance in the judging criteria of landing moves such as those seen in the video, means that surfers will need to spend time working on their technique.

With the help of video analysis they can assess their aerial maneuver take off positions, the height they attain and other factors during flight such as rotation. Landing positions that will allow the surfer to ride out of the maneuver and into the next one, require excellent balance and technique. All these factors which will lead to progressive moves can and should be analyzed.

The analysis can then help them to add height or variety to their moves, impressing the judges further and blowing the competition away.

Most pro surfers have hours of video footage of themselves to analyze. However many of these are shot for cinematic effect and may not give the best angle for analysis. With the new criteria pro surfers will also want to get video that will give them the best analysis possible.

For the rest of us, watching video of pros and capturing video of ourselves for analysis will allow us to improve our technique and general surfing. Please browse our site for suggestions on cameras and how to get great footage to do just this and contact us to let us know how you are getting on.

Fastest Ball Sports

2010-03-30T11:38:00.000-07:00

Debate about which ball sport is the fastest can be heated. There are many that suggest that Jai Alai (pronounced Hie Lie in English) with ball speeds clocked at 188 MPH is the fastest. The golf drive and badminton smash are also in the mix and may reach even faster speeds. Some have even suggested paintball as the fastest, but we will draw a line there and rule it out as not a ball sport.

Below is some video of Jai Alai. The ball used in Jai Alai consists of metal strands tightly wound together and then wrapped in goat skin. The ball weighs 4.5 to 5 ounces.

Now that you have a feel for Jai Alai, take a look at this Sports Science episode in which long hit golfer Jason Zuback tries to break the 188 MPH ball speed mark set by Jai Alai. As you watch remember that a weight of a golf ball must not exceed 1.620 ounces.

Watching this it seems there can be no question. Zuback's 204 MPH monster drive suggests that golf is the fastest ball sport.

Unfortunately in this Sports Science episode and watching Zuback drive the ball we have no idea how accurate his drive was. He may have imparted 204 MPH to the ball, but if that ball does not go straight down the fairway, that extra power will only put him deeper into the rough.

In his first few attempts, Zuback reaches speeds just under the 188 MPH mark. As long distance driving requires ball speed and accuracy, it is possible his accuracy suffered in his attempt to hit almost 20 MPH faster in his final attempt.

As Jai Alai is played on a court with walls, we will assume that the 188 MPH ball speed recorded is the ball speed that could be reached in the actual sport. While the 204 MPH recorded with the golf drive may not in fact have resulted in a useful golf shot or even long ball drive.

Now think about the mass of the ball in both sports. Newton's 2nd equation of motion states that the less mass (lighter) the ball, the faster it will accelerate and therefore the more speed it will have for the same amount of force. With that idea we can see that the Jai Alai ball which weighs 3 times as much as the heaviest golf ball will require greater force to reach the same speed.

If we were to rephrase our debate and ask which ball sport creates the most force and power, we may now have another argument on our hands.

Video Analysis can help us to analyze these high speed ball sports and others. With video and some inexpensive analysis software we can determine how the athletes create these tremendous ball speeds and possibly (with the right equipment) measure these speeds and even the forces.

Impact Forces in Barefoot Running

2010-03-25T10:58:00.000-07:00

A recent thread discussing barefoot running impact forces on a biomechanics user group, reminded me of another important aspect of barefoot running and the main reason many researchers, runners and scientist are suggesting that it may be better to run barefoot than in shoes.

The impact forces are the forces that the muscles, ligaments, tendons and bones experience when the foot first hits the ground. Impact forces are absorbed by the foot and transferred and shared among all the muscles in the leg and up to the hips. Research has shown that this impact force has a higher impulse (change in force over a time period) when landing on the heel than when the runner lands on his mid-foot or forefoot.

Running in shoes has allowed runners to feel comfortable landing on the soft cushioned heel of the shoe and therefore the impact forces and impulses are increased sending larger shock waves through the body and possibly causing injuries. Barefoot running, forces the runner to land on the mid-foot or forefoot, reducing the impact forces and impulses.

The video below from the Nature channel on YouTube about the barefoot professor, Harvard professor Daniel Lieberman, gives a good explanation of the theory. Professor Lieberman also published an article in Nature magazine on barefoot running. Notice how they use video analysis to analyze the running mechanics. They also use force platforms in the treadmill that measure the forces. Force platforms are like large accurate bathroom scales that can determine the position of the foot.

There seem to be advantages to barefoot running, but there are many unknowns too. Even if there are advantages to barefoot running in lowering impact forces and the foot control that may reduce pronation, we may not be aware of the disadvantages that exist.

Barefoot running definitely seems to increase blisters, bruises and pain under the foot. The calf muscles are often more sore and stiff after running barefoot and other muscles may also be strained in ways that cause different injuries.

So if you plan to try running barefoot, start slowly and build up your tolerance and strength. Also record some video footage of your running and try to identify how you run differently in shoes and barefoot.

We are ready to help you with this analysis. Please contact us to see what we can do.

Golf Swing Sequence

2010-03-16T17:33:00.000-07:00

The golf swing is regularly analyzed by golf pro's using video. Each has their own explanation for what makes a good swing.

A good golf swing is the result of perfect timing and sequence. The video below gives an interesting analysis of the timing and sequence of a golf swing.

As you watch, think about the Kinematic Sequence that we have discussed in a previous post on Tiger Woods swing

The Kinematic Sequence is best measured in 3D but a simple explanation can be given.
The kinematic sequence is the sequence and timing of events in the golfers down swing that will transfer energy and speed from one body part to another and finally to the golf club to launch the golf ball.
When the 3D kinematic sequence is measured by companies such as Titleist Performance Institute, they measure the rotational velocity of the hips, shoulders, wrists and club.

On the down swing

The hips should start to rotate first and reach their peak rotational velocity first.
The shoulders should follow closely behind the hips but the shoulder rotational velocity (speed) should peak just after the hips. The shoulder velocity should also be higher than that of the hips.
The wrists (forearms) follow, reaching their peak after the shoulders and once again reaching a higher peak.
Final the club follows through the swing peaking last and with the highest velocity.

If we look at this sequence in a graph we see each rotational component leading into the next and building to the peak club head velocity.

We consider, The 3D Guy, Phil Cheetham to be the Golf Biomechanics Guru. His blog is an excellent place to learn about the kinematic sequence for golf in even more detail.

Now take a look at this video and see how the same concept is described differently.

This video is a great example of how a coach can use video analysis and explain similar concepts in a different way. The trick is to find the explanation that will help you understand what you are looking at and makes you a better player. If the idea of the kinematic sequence is confusing then maybe the idea of a multi stage rocket will make more sense.

If you are looking to do analysis and need some guidance, we can help you.

The Winter Games Are Still On In Vancouver!

2010-03-15T15:18:00.000-07:00

Winter is still in full force in Vancouver, BC, and the action is just getting started with the 2010 Paralympic Winter Games. Athletes from around the world are gathered to compete in a variety of events few of us would have the nerve to even attempt.

During this year's opening ceremony, the flag bearer for the USA team was Heath Calhoun, a veteran of the US Armed Forces. Heath lost both his legs while on patrol in Iraq, and spent nine months of rehab at the Walter Reed Memorial Hospital. Since 2008, he has been training to compete in this year's Paralympic Winter Games - specifically the men's sit-ski slalom and the men's sit-ski super G.

Please join us in supporting Heath and all his fellow athletes in this year's games. Information and video highlights of the US team can be found here: http://usparalympics.org/

Note: In late 2007, I had the privilege of installing a motion capture system at the Walter Reed Memorial Hospital. The system is used to study the effectiveness of various prosthetics and rehab techniques on many of our nation's wounded veterans. I was honored to meet some of the brave men and women who were injured while serving in our military, and was inspired that motion capture and video technology plays such a big role in their recoveries.

Mastering the Basketball Block

2010-03-13T17:57:00.000-08:00

Lebron James is definitely the master of the block on the basketball court. His chase downs are always spectacular and fun to watch.

There is a lot we can learn from watching Lebron's blocks particularly how he jumps keeping his head up and following the ball at all times with his eyes.

Here is some video of Lebron's top 10 blocks so far this 2010 season.

Running in Minimal Shoes

2010-03-09T07:24:00.000-08:00

A large following and interest in barefoot running has been developed lately, encouraged by Christopher McDougall's book "Born to Run" which describes the Tarahumara or Rarámuri, an indigenous peoples from Northern Mexico, who have been known to run long distances in thin soled sandals. We recently assisted a runner with some video analysis as he trains to run a marathon wearing the Vibram FiveFingers minimal shoe.

Last year we discussed using video analysis to analyze rear foot pronation and attempted to see whether there was a difference in rear foot pronation between running in shoes and running barefoot. We described how a camera should be setup and the measurements that could be done. However, as we studied a runner who does not suffer from pronation we were only able to see a normal amount of pronation in the foot stance phase of his running.

Our runnerwanted to determine how much he was pronating when running in his FiveFingers minimal shoes. He also reported getting blisters under the pads of his feet and on his right big toe.

He used all the techniques for filming his motion that we have discussed on this website in the past and sent the videos on to us. He set up to run on a treadmill at a constant speed of 8.3 miles per hour and ran 12 miles in total capturing video at intervals along the way. Set his camera on a tripod at the level of the treadmill to capture the video and his foot placement. He captured video both from the side view and the rear view so that we could assist him in analyzing his foot strike. Take a look at the video below.

From the video we have taken a few snapshots to help us analyze his foot strike characteristics.

In the images above we can see a side view of the left and right foot strike. We can see that:

Both the left and right foot is inverted at foot strike. This means the feet are turned in and the athlete lands on the outside of his foot.
The main muscle used to invert the foot is the Tibialis Anterior (the muscle on the outside of the shin bone). These muscles are also used to dorsi-flex the foot (lift the foot up). This can be seen in the video as the foot and toes are flexed back just before foot strike.
Striking with an inverted foot can create a slapping of the foot onto the ground rather than a controlled foot placement.
Striking with an inverted foot can also exaggerate any rear foot pronation.
The foot strike is occurring toward the midfoot and not the heel. This is to be expected when running in minimal shoes. The runner in minimal shoes is trying to avoid heel impact and is taking greater care to control his foot strike.

Now we can look at his rear foot pronation. In this instance an estimate was made for rear foot pronation using a 4 point angle. Rearfoot pronation is measured as the amount of eversion (rotation inward) of the foot from heel strike through mid stance. The angle is measured by drawing a line along the center of the Tibia bone in the lower leg and another line describing the center line of the Calcaneus (heel bone).

As our runner was concerned that he was pronating more in his right foot, we have looked only at his right foot here:

The pronation angles displayed in the images above are estimates. As there are no markers identifying the necessary landmarks of the midline of the Tibia and the midline of the Calcaneus.
The athlete lands with an inverted foot position. The rear foot pronation angle of 171 degrees shows this. An angle of 180 degrees would be neutral while anything over 180 degrees is everted (pronated).
At mid stance the athlete has 13 degrees of pronation (193-180). The foot is expected to evert (pronate) by approximately 10 degrees through mid stance for normal pronation. Therefore this would be considered excessive pronation.
The eversion of the foot from foot strike to midstance is also rapid and large, pronating 22 degrees.

As can be seen from the video and the images our runner pronates while running at 8.3 miles per hour.

Our runner has been training in his Vibram FiveFingers shoes for less than 2 months. Prior to running in these minimal shoes he ran in a shoe offering maximum pronation support. It may therefore be too early to tell whether the minimal shoes are improving his pronation by encouraging him to control his foot placement.

Our runner has also been suffering from blisters, since wearing these shoes. Unfortunately a minimal shoe such as this will likely cause the foot to blister more readily. The shoes are worn without socks (as each toe is separated in the shoe)causing more friction between the shoe and the foot. Being that there is not much cushioning between the shoe and the road surface, any scraping on the hard road or treadmill surface will also cause friction and possible blisters.

It is possible that our runner is in fact suffering from the effects of his blisters and is running as seen in the video because of the blisters on his foot. The exaggerated inverted foot at foot strike may be a way of attempting to protect his foot from injury and further blisters.

We still believe that barefoot running or running in minimal shoes will help to improve a runners mechanics. Barefoot Ken Bob Saxton says, “Don’t strike the ground. If you do it’ll strike back!” The idea of running barefoot or running in a minimal shoe is to feel your feet and understand how much they can take and to learn how to control your running so that you can continue running faster and with less injury.

If you want to try running in minimal shoes, allow yourself sufficient time to get accustomed to running in them before trying to do to long a distance at too high a speed.

Also pull out your video camera and film yourself. This will help you to visualize what you are doing and possibly help you to achieve success in a minimal shoe. We are always ready to offer our services to help you analyze your motion.

NBA's Dirtiest Players Can't Hide from the Cameras

2010-03-03T13:29:00.001-08:00

A Sports Illustrated Poll this week announced the dirtiest players in the NBA.

Top of the list is Reggie Evans of the Raptors with 21% of the vote, far ahead of Ron Artest of the Lakers with 13% .

No argument here, Reggis Evans is definitely the dirtiest player I have watched. Ron Artest has a been a little subdued since his move to the Lakers, but he is an aggressive defender and gets in opponents faces and has played dirty in the past.

Playing aggressive defense is very different from playing dirty. There is absolutely no reason for dirty play of the likes that can be seen in the video of Reggie Evans below.

Video Analysis can be used in different ways and reviewing dirty plays is one other. Thankfully the number of TV broadcast cameras covering every inch of the basketball court ensures that no dirty play can be missed.

In European soccer, video replays of fouls and off the ball incidents can be reviewed after the game and players can be fined and/or suspended based on the video evidence.

Here is a video of Reggie Evans dirty play against Chris Kaman in the 2006 playoffs. He was not suspended for this action although he was fined.

The NBA however is not generally dirty. There are very few occasions when it would be necessary to review the video and suspend a player.

But, did Evans really expect to get away with this, when there are 3 or 4 camera angles focusing on the play. If the cameras and the notoriety of playing dirty and being seen by millions cannot prevent this type of play, then perhaps the NBA should employ a similar strategy to soccer and suspend players for dirty off the ball incidents.

Beauty and Grace on Ice

2010-02-27T09:59:00.000-08:00

Scoring a record (combined short program and free skate) 228.56, South Korean superstar Kim "Queen" Yu-Na, took home a gold medal in women's figure skating, a first for her country. Her scores for both the programs set new records, although it was her brilliant performance in the short program that set the tone for her competitors. She scored so well, in fact, that it was speculated she could have two major mistakes in the free skate and still have a good chance to win gold.

Unfortunately, the only videos of this year's Olympic performances by Kim can be found on NBC, which may only be viewable to people in the United States.

But we've found some older videos of this superstar (as well as other figure skaters) for you to enjoy. This video includes some nice slow motion and zoomed-in enhancements which allow for a more detailed analysis. With figure skating videos, it's difficult to accurately calculate angles and distances, as the camera and skater are rarely positioned perfectly at the key positions of the movements; but the poster of this video does his best.

The 2010 Winter Olympics will be ending soon, but we've certainly enjoyed watching all these amazing athletes performing at the highest level. Despite facing some additional natural challenges (e.g., poor weather), this year's Olympians have put together some terrific runs that we'll be able to enjoy watching for many years.

Shaun White: McMission Accomplished!

2010-02-18T21:30:00.000-08:00

King of the Hill. Master of the Half-Pipe. Call him what you will; Shaun White defended his 2006 Olympic title with a series of dominating performances in the 2010 Vancouver Winter Olympic games.

His first run scored so high that he didn't even need to break out the stunt he'd been working so hard on - the double McTwist 1260. But having locked up the gold medal, he decided to throw in this amazing trick at the end of his second run, much to the delight of the crowd. With just barely enough speed, he launched himself into the air, performed the two flips, and just barely came around on the last of the 3 1/2 spins. An analysis of the double McTwist 1260 can be found here.

After reading the analysis, check out a replay of both White's 2010 Olympic performances.
or below:

Shaun White's Gold Medal Winning Half Pipe Run [2010 Olympics] - Watch more Sports Videos at Vodpod.

For more information on this year's team representing the USA, please visit: http://teamusanews.org/.

Go USA!!! Go World!!! (but mainly, Go USA!) :)

Winning on the Turns in Speed Skating

2010-02-18T11:05:00.000-08:00

His win in Vancouver makes Shani Davis the first male long track speed skater to repeat in an event at the Winter Olympics.

Watch the event here

All the experts say that Shani has the best turns in speed skating. He definitely looks like he can go faster than anyone else on the bends.

We decided to take a look at some video of Shani breaking the World Record for the 1500m in Salt Lake City in December 2009.

The high definition quality of this video allows us to look closely at his turns.

There are 3 things to look out for:

In both the inside turn and the outside turn Shani increases his step rate (cadence) than that on the straight. He needs to do this so that he can make the turn, but the increase in step rate also ensures that he maintains his speed from the straight away and into the next straight.
As his step rate increases his right arm swings in rhythm with his steps. This means that his arm swing rate also increases. In all sprinting sports, pumping your arms helps to maintain balance but it also powers you forward in the sprint.
His inside leg pushes to the outside of the track with each step. As he pushes this left leg goes underneath the right leg, allowing him to apply more force to his push off for longer.

OK, so all of the top speed skaters skate like this right. What makes Shani so much better in the turns?

Shani at 6' 2" is a little taller than some of his closest rivals like American team mate Chad Hedrick at 5'11" and Dutch skater Sven Kramer at 6'1". Taller athletes will generally have longer legs. Leg length can definitely help when taking the turns. The extra leg length can add that little bit of extra time during the push on the ice.

But leg length is not going to help you if you don't use it to your advantage.
In the turns, it is also important to have great flexibility so that your inside leg can cross under the outside leg and keep pushing for longer. Shani seems to have gymnastics like flexibility and is able to push his inside leg far under his outside leg giving him more time on the ice than his competitors to push in the turn.

Flexibility though is of no use in speed skating without incredible strength. Shani's powerful legs allow him to continue pushing hard even when his legs are crossed over.

So Shani is the best skater on the turns because he uses his long legs, flawless technique and exceptional flexibility and strength.

Some athletes may never have the perfect physiology or anatomy to be the best, but one thing we can all work on is flawless technique. Video Analysis can help us achieve that.

What it takes to compete in Freestyle Aerials

2010-02-16T12:49:00.000-08:00

In our previous posting, we discussed the technique used by Freestyle Aerialist Anton Kushnir. In such a challenging and potentially dangerous event, it takes a variety of skills for an athlete to be successful.

One of Team USA's hopefuls this year is Olympic veteran Emily Cook. Growing up, Emily participated in gymnastics and skiing events; when she learned about the Freestyle Aerial event, she recognized her chance to combine her passion for both sports. There's a nice interview with her at: http://www.teamusa.org/video (search for Emily Cook).

We've also found a really nice compilation of videos that shows Emily's progression over the years. While Emily's gymnastics background undoubtedly helped her succeed in this sport, the video shows it's taken her almost an entire lifetime of hard work and practice to make it to the Olympic level.

We wish Emily and the rest of this year's winter Olympians the best of luck in Vancouver, and look forward to watching all of the events! Go Team USA!

Freestyle Skiing Aerials

2010-02-11T08:19:00.000-08:00

Freestyle Skiing Aerials is the springboard diving of the Winter Olympics. Athletes complete huge back flips and twists after taking off from a ramp with takeoff angles ranging from 60 to 70 degrees.

Athletes are judged on their take off, the height attained during their trick, the control, form and body position during the trick, and how they land and ski out.

Some male athletes such as the World Champion, Anton Kushnir from Belarus can attain heights of 50 feet or 5 stories during a trick. In comparison the highest jump height in a half pipe was achieved in 2010 by Peter Olenick at 24 feet 11 inches.

Below we have some video of Anton Kushnir, favored to win the gold medal for Free Style Skiing Aerials in the Vancouver Olympics 2010.

Here Anton is performing a near flawless trick with 3 back flips and 4 twists.

Analyze the video closely and you will see that Anton completes his first twist in his first flip on his way up. He then completes 2 twists in his second flip and the last of his 4 twists in the third flip.

The slow motion video also allows us to analyze and understand how Anton maintains good form and is able to land so smoothly out of the trick.

After each flip notice how he ends with his body in an upright position and how he slows down his twist. He even opens out his arms to help him slow down his twist.
He does this so that he can review his position and height in the air before moving into the next part of his trick.

Being aware of your body and spatial positioning in a big complicated trick like the one performed above is essential. If Anton began to twist off axis or drift laterally (to the side) during the trick, he would find it much more difficult to complete.

By "spotting" his position between each flip he is able to make any small corrections prior to the next flip, or in an extreme case to abort the trick and try to land safely.

We also see in the slow motion replay how Anton uses his arms and head during the second flip with the 2 twists to speed up his twisting motion. In the first and last flip he is only completing one twist and uses his arms minimally. In the second flip, by turning his head in the direction of his twist and bring his arms into his chest he is able to spin faster and complete 2 twists.

Form and landing are also critical components of the Aerial trick. We can see that Anton keeps his legs tightly together and his body straight during his flips and twists, for perfect form.

On landing he brings his arms forward and together in front of him and bends his knees into the land. When landing from 50 feet or more on snow or any hard surface your knees have to bend quite a bit to absorb the impact of landing.

Keeping his arms out in front and his head still and looking forward as he lands, he is also able to ensure he does not fall back on landing and can ski out of the trick.

So what's the biggest aerial trick we may see at the Olympics in 2010. US aerialist Jeret Peterson plans to attempt his "Hurricane", which consists of 3 flips and 5 twists (one more twist than in the video above). We also may see some other big tricks from Anton and other contenders.

Please contact us if you have any questions or are interested in analyzing your performance. Video Analysis is not only for the pros. It is great for any sport in which mechanics, form and technique are important. This covers just about all sports, except Poker :).

The Triple Axel in Slow Motion

2010-02-03T12:53:00.000-08:00

Performing a spinning jump in figure skating is all about proper mechanics. As we look forward to the Winter Olympics 2010 in Vancouver, we found some video of Stephen Carriere performing a Triple Axel on the Discovery Channel's Time Warp program.

A triple axel is a figure skating jump that takes off facing forward and jumping forward, the skater then rotates 3.5 times and lands on the opposite foot skating backward.

As this video is from Discovery Channel it cannot be embedded, but please watch it here
http://www.youtube.com/watch?v=aixweBf9qFY .

Time Warp explains that Stephen skates at a speed approaching 20 miles per hour and takes off at an angle of 45 degrees. Unfortunately the camera view used in the video makes it difficult for us to measure these values. However there are many other mechanical aspects of the jump that we can analyze with this video.

The first part is the take off. From this high speed video we can see how Stephen Carriere creates the rotational speed necessary to complete the three and a half twists.

Stephen is jumping off his left leg and as he prepares for the jump he bends his left knee and allows his right leg to drag behind him. From this position he swings his right leg in a small arc around his body. At the end of the spin he drives the right leg up and simultaneously jumps off his left leg. The combination of spinning and jumping at take off gives him the height and rotation necessary to complete the quad axel.

Once he is in the air Stephen keeps in a tight twisting position. Notice how his chin is tucked down toward his left shoulder (in the direction of his spin), his arms are pulled into his chest and his legs are crossed making sure they stay tightly together.

Athletes who get less height than Stephen often have to spin faster and do this by turning their heads and arms further in the direction of the spin. We can see that as Stephen enters his third rotation he does turn his head further in the direction of his spin.

The video also gives us some insight into the landing. To land, Stephen needs to slow down his spin and stop his head from rotating so that he does not fall. He opens his arms out to slow the spin and stops his head. This allows him to "spot" the position for the landing. "Spotting the position" does not mean he looks at his feet to see where he is going to land, but rather that he has chosen an object at eye level that will inform him of his position prior to landing. "Spotting" is an important aspect for all spinning moves.

In the video we can also see that Stephen starts moving his left leg away from his right landing leg just before touch down. Landing with his legs crossed would not allow him to absorb the impact of landing and skate out of the jump. On landing he bends his right knee to absorb the impact and swings his left leg in a wide arc, opening up his body and slowing his rotation.

Unfortunately we won't be seeing Stephen Carriere at the 2010 Olympics as he recovers from an injury, but we will see others performing this trick and hopefully can get more slow motion video.

Using high speed video can definitely assist in analyzing your performance. If you are looking for assistance with using video to analyze your sport, please contact us. We look forward to your comments.

What Makes Federer's Game "Classic"?

2010-01-28T09:47:00.000-08:00

Many writers describe Roger Federer's game as "classic," but what exactly does this mean? The word itself means "something that is a perfect example of a particular style, something of lasting worth or with a timeless quality" (Wikipedia).

With video analysis, we can easily compare Federer's style of play with previous generations' players by viewing them side-by-side, looking at stillshots of key positions, and synchronizing the video to a particular event (e.g., impact). Below we have a video comparing Federer's game to a champion of the past, Bjorn Borg.

The key positions shown here are: Preparation (a.k.a. Loading Phase), Contact, and Follow-through. During the Preparation phase, both players bend their knees and rotate their upper bodies, building up potential energy. They're also using an open stance, meaning their front foot is not positioned across their body. The second key position shown in the video is Contact; and it's noted that both players impart topspin on the ball by brushing up the back of the ball from a low to high position. The final key position is the Follow-through. Because they swung from low to high, both players' racquets end up across their bodies from somewhat of a windshield wiper motion.

What makes the similarity between these two players' styles so interesting is how different their racquets are. The physical properties of the racquets are quite different, including the size, weight, material, and string; and these differences undoubtedly affect the types of shots a player can make on a ball. But despite these differences in racquet technology, Federer's technique on this forehand is extremely similar to Bjorn Borg's, and that is one of the things that makes his game classic.

Breaking Down Shaun White's Double McTwist 12

2010-01-28T07:24:00.000-08:00

The Vancouver Winter Olympics are rapidly approaching now. One event I am personally looking forward to is the Men's Half Pipe Snowboarding event on February 17th.

We all know that in this event, Shaun White is the man to beat. The defending men's half pipe champion recently unveiled a new trick that he will likely perform at the Olympics, the Double McTwist 12.

Sounds really complicated, but what exactly is it? Below is a video of Shaun white performing this crazy trick. We can use the video to break the trick down and understand it better.

We can start with the obvious, the 12 in the trick name refers to the number of twists. Shaun is rotating 3 and half full twists or 1260 degrees. It is pretty hard to pick that up as he needs to twist so quickly to finish the trick.

A McTwist is a 540 degree spin (or one and half rotations) with a flip in the middle. Double the McTwist would be a total of 3 rotations and 2 flips.

Therefore the Double McTwist 1260 can be broken down as a half pipe aerial with 2 flips and 3 and a half twists. If you watch the slow motion replays of the trick you can pick out the two flips and spot the beginning of each twist.

Look out for this trick on February 17th in Vancouver and possibly other new tricks by Shaun's competitors.

We love to hear comments on our posts.
Please also contact us if you have any sports video, biomechanics or motion analysis needs.

One Hand or Two Handed Backhand in Tennis

2010-01-21T08:40:00.000-08:00

The backhand tennis stroke has transformed incredibly since the 1980's and now the majority of men and most of the women players use a two handed backhand. In fact in men's Tennis only Federer of the top players playing the 2010 Australian Open this week, uses a one handed stroke.

The backhand can be used for a variety of shots and there are distinct advantage of a two handed backhand over a one handed backhand in most instances.
Damir Popadic breaks it down shot by shot on the ITF coaching website and suggests which shot is better and why.

Return of Serve - Two handed is better as it allows the player to use a short back swing and to play the stroke with an open stance (hips facing forward).
Running backhand - Two handed is better as a single handed stroke requires better positioning. A one handed stroke requires a rotation of the hips and shoulders and a longer back swing making it more difficult to hit on the run.
Approach shot (to the net) - Two handed shot allows the shot to be hit with an open stance which gives the player more time to approach the net. The player does not need to complete his rotation before approaching the net as he would with a one handed shot.
Low balls - Two handed shot allows for more stability and it is easier to scoop the ball up with a stable base. The one hand shot will be difficult to control.
Short low balls - Popadic suggests that neither shot has the edge here, but the one handed shot has the advantage of reach and with a strong wrist a satisfactory shot could be played.
Very wide balls - here again Popadic gives no advantage either way, but just like the short low ball, the one handed shot has the extra reach and a strong wrist action (such as Federers) could produce a fantastic shot.
Balls hit at the body - Here the single handed backhand has the definite advantage. With a single handed shot the player is able adjust his racket position enough to block the ball back.
Slice shot - Now here is a shot that can only be played one handed. This is also an important shot for defense and staying in a rally. It is also a great shot to use to change the pace of a point. There is no good way to play this shot two handed and therefore even a player with a two handed backhand will need to play the slice one handed.

It seems from Damir Popadic's analysis that the two handed stroke must be far superior to the one handed backhand. However we all know the world number 1 tennis player, Roger Federer, uses one hand and seems to have as much power and precision as the other top 10 players using two hands.

Most pundits though believe that Rafael Nadal and Andy Murray's two handed backhand is better than Federer's one handed version. But lets take a look at two down the line drives, one from Federer and the other from Andy Murray. Although I believe Nadal has the best backhand in tennis today, it is more difficult to make a comparison because he is a left hander.

Although both these videos show a backhand drive down the line, you will notice that they are not filmed from the ideal position and Federer's shot is from a waist high ball, while Murray is hitting a ball around chest high.

It is interesting to note that with a backhand drive both players need to setup correctly, turning their hips and shoulders 90 degrees to the direction in which they are going to hit the ball and taking big backswings. It looks as if Federer's backswing is bigger than Murray's, but with the different camera angles it is not possible to be definitive here. So the two handed advantage of a more balanced, open stance does not apply when comparing these two backhands as both players use a closed stance.

Watching the shot itself, we see Federer rotate his hips and shoulder further away from the court to create potential energy (wind up) just before the shot. He then swings through the ball using both his hips and shoulders to create power, hitting the ball almost in line with his body to ensure that it goes straight down the line and not cross court.

Murray on the other hand rotates 90 degrees to the court in preparation for the shot but then does not rotate further away to increase his potential energy. This is a result of the two handed grip he uses and possibly also because the ball is bouncing high. You will see that although he does rotate his shoulders toward the ball, it is not nearly as much as Federer's rotation. Instead he create power by using both arms to hit the shot. He too meets the ball with the racket in line with his body.

The follow through of both players is also of interest. Federer follows through all the way opening up his shoulders and finishing with his racket above his head. Murray's follow through is almost as big but he does not take the racket high above his head because both hands are on the racket.

So which backhand is better?
Federer is using his whole body, with a big back swing and follow through and lots of rotation to create power. He needs, and does have a strong wrist and forearm and is able to control the ball with that strength.
Murray uses his two hands to control the shot, but also needs to take a big back swing and follow through and to rotate his shoulders in order to create power. He supplements that rotation power by using both hands.

Both backhands are powerful and precise. When Federer's backhand goes wrong though it can go horribly wrong, but if he gets it right with timing and position he is often hitting a winner. Murray is less likely to hit a wild backhand shot.

Federer though seems to have a much wider variety of backhand shots than Murray or even Nadal for that matter. Nadal and Murray may hit heavier backhand topspin shots, but Federer seems to be able to flick and block and change his shot whenever he pleases.

As the two handed backhand seems to be more efficient and better for players with less racket control and wrist strength (everyone other than Federer), it is likely that we will see less players using a one handed backhand. For now we can enjoy watching Federer's backhand mastery and compare it to the awesome power and control of Nadal's and Murray's.

Have a great week.

Analyzing Ski Jumping Video

2010-01-13T15:44:00.000-08:00

The 2010 Vancouver Winter Olympics starts February 12.

One of my favorite events to watch is the ski jump. The athlete takes off down a long steep ramp and launches off the end off the ramp in attempt to gain maximum distance. Athlete's are also scored on their style on take-off, through the air and on final landing.

What I enjoy most about watching ski jumping is the ease with which this sport can be analyzed and technique improved using simple video analysis. Most of the analysis of pro athletes can even come directly from TV broadcasts, because the best views to watch the sport are often also the best angles to analyze it.

Below we have some video of Janne Ahonen, of Finland jumping a huge jump at World Cup in 2009.

Note particularly in the replay that the broadcast uses a front on view of the jumper. We Can see how he pushes off for the take off and how he corrects his body position through the air, both for style and to obtain maximum jumping distance. Finally we can see him prepare for the Telemark landing. The Telemark is a landing style with one foot in front of the other and scores higher style points for the jumper.

We look forward to a great year of sports and video sports analysis in 2010. Look out for more features during the Winter Olympics.

Dribbling the Basketball While Running

2009-12-14T14:00:00.000-08:00

Basketball as a sport can be made to look so easy. We watch Lebron James dribble the ball down the right side of the court while he surveys the positions of his team mates and the opposition. Suddenly he breaks left toward the basket, switching his dribble to his left hand, one more step and one more bounce then he switches back to the right hand as he elevates for the dunk.

Not once in this sequence does he look at the ball (until it is going through the hoop). As he does each movement, including side steps and head fakes, he keeps the ball bouncing slightly out in front and to the side, positioned ready for the next spectacular play.

Dribbling the ball is an essential part of basketball. A player that can dribble with confidence and control will have more options to attack the basket and get good looks to shoot a jump shot or attack the basket for a lay up or dunk.

We collected some video of a player running and dribbling the ball with his right hand, as well as some close up video of the players hand while he bounces the ball while standing.

We set up the video camera on the side of the court so we could watch the player run through the camera field of view. This allows us to see where he bounces the ball as he runs through. If the player ran toward the camera we would be unable to determine how far in front he pushes the ball.

The close up video of the hand will show a good example of how to bounce the ball in the dribble.

A correctly inflated basketball should bounce most of the way back up to your hand if you simply dropped it. You only need to push the ball down with enough force to get it back to your hand. Push too hard and the ball will bounce higher than expected and you may lose control.
Bounce the ball off your spread fingers. You do not want to push down with your palm. Allow your fingers to feel for the ball as it bounces up and then spread your fingers and push down on the ball for the next bounce. Push down by bending flexing (bending) your wrist.
Keep your head up surveying the court and position of your team mates and the opponents. You should do this whether you are running with the ball or simply standing still.
Keep your legs slightly bent and be ready to make your move. You do not want to be caught back on your heals as you are dribbling the ball as this makes it easier for an opponent to steal the ball. Be in a position ready to move.
Although we do not show this in the video, you should learn to dribble with both hands and on both sides of your body. This will allow you more options when driving toward the basket or preparing for a pass.

Now take a look at our player in the first part of the video as he runs at 3/4 speed while dribbling the ball. Dribbling while running fast can put your opponent off balance and create room for yourself and your team.

Here are a few tips to keep in mind when dribbling and running:

Once again, do not look down at the ball. You need to trust that the ball will bounce where you want it. This may be difficult at first but will come with practice. When running and dribbling it is even more important to keep your head up and see the court and be prepared to change direction quickly.
Bounce the ball far enough out in front of you so that you do not need to check your run to keep control of the ball. Many a fast break will come to nothing if you need to slow down to get control of the ball.
Bounce the ball out a little to the side. If you are dribbling with your right hand keep the ball a little outside and far enough in front of your right leg. If you bounce the ball directly in front of you then you will have more difficulty controlling it as you run. Of course if you are about to cut in toward the basket then you will need to bounce the ball in front of your body, but then you will also be turning your body or switching dribbling hands and will still be keeping ball slight outside your legs.
Once again use your fingers to bounce the ball and push it out in front of you. Do not use your palm as you are likely to lose control and probably the ball if you are running fast.

Practice will help you learn any new skill or get better at it. The more you practice the easier you will find the skill as your muscles and body learn what to expect and anticipates the limb movement and muscle action required.

We often say watch video of pros and of yourself and then practice with this in mind. Watching pros allows you to see how it should be done. Watching yourself ensures you know how you compare to these pros. Both are important. If you practiced all day but had no idea what you were doing wrong, you could teach your body to perform the skill incorrectly.

With video technology today there is no reason why you cannot easily assess your own performance. Take a look at previous articles in this website to find more tips on filming yourself or how to do specific skills.

Happy Holidays

The Snowboard Ollie

2009-12-07T07:20:00.000-08:00

Winter is definitely here and many of us will be heading to the slopes this season for some skiing or snowboarding. When heading out, it is a great idea to have a trick or skill in mind that you plan on learning. Anything from slaloming on skis to riding your first rail on a snowboard will help to motivate your sessions on the slopes and ensure you do not get too frustrated with crowds.

Whatever trick it is that you plan on learning, see if you can find some video of it being done. Study the video carefully and keep it in your mind as you try the skill once you get out on the snow

We will keep it basic this time and take a look at the snowboard ollie. We have discussed the ollie in skateboarding in a previous post. On snow and a snowboard the trick is performed similarly. As in skateboarding, the ollie is the basis for most aerial tricks on a snowboard and therefore it is important to learn how to do a great one.

Try the ollie from a standing position first. Get used to the mechanics of the movement before you try the jump while moving.
Start with your knees bent and body upright. You do not want to bend at the hips and lean forward or backward. If you do you will have difficulty landing your ollie as you will have started the trick off balance. Bend at your knees a little though to give you some spring.
To start the trick, push down on your back foot moving your center of mass backward over your back foot. This will allow you to pull the front of your snowboard up and prepare you to jump off your back foot. Remember that a snowboard is also pretty flexible so pushing down on your tail will bend the board giving you some spring into the air.
As the nose of your board begins to pull up into the air, jump off your back foot so that your back foot comes as high as your front foot. To get higher into the air, pull your front leg higher up and jump higher off your back foot to allow your back leg to catch up in the air.
Once your back foot and front foot are at the same height position yourself over the center of the board and stabilize yourself for landing. Your center of mass should now be in between your feet.
Land on both feet evenly, so that you do not slide out once you hit the ground. Once again do not bend at the hips. Bend your knees slightly to absorb the landing.

Take a look at this video of a small ollie on a snowboard.

Watch lots of videos of the pros and film yourself to see if you can improve your style or get higher in your ollie or any other trick you try this winter.

Have fun in the snow.

Evaluating and Comparing your Broad Jump

2009-11-30T09:58:00.000-08:00

The broadjump is a drill used to measure how far an athlete can jump from a standing position. The NFL has potential players perform this exercise during its annual combine, and uses the results as one of the many ways to evaluate the athletes' power. Below we have synchronized two athletes' broadjump trials. We've also slowed down the side-by-side video to help with the comparisons. And beneath the video window, we've included stillshot images of each athlete during key positions of their trials.

1. Loading Phase
During the loading phase, the athletes swing their arms back, in preparation to swing them forward. They will use this forward momentum to help them jump as far as possible. Also, notice their hips, knees, and ankles are all flexed (sometimes referred to as "triple flexion"). By flexing at these joints, the athletes are building up potential energy that will be released during the liftoff phase. From these two images, we see that the second subject has a slightly deeper knee bend than the first subject.

2. Liftoff Phase
During the liftoff phase, the subjects swing their arms forward and upward, and use this momentum to help propel their bodies forward. We see that the first subject extends his arms all the way, while the second subject has his arms flexed at the elbows. The second subject can definitely improve his form by extending his arms fully. Driving your arms forward as far as possible will allow you to use all the energy your arm swing can provide.

Also worth noting, their lower bodies also go through "triple extension" now (hips, knees, ankles), converting the potential energy into kinetic energy. We see that both subjects take off at about the same angle relative to the ground.

3. Maximum Height
In the pictures below, we see the key positions showing the subjects' centers of mass (COM) at their maximum heights, and at what distance from the start their maximum heights occurred. An athlete's COM during a jump follows a path similar to that of a ball flying through the air - in other words, it follows a parabolic arc. It will reach its highest point midway between the distance it is thrown. By driving your arms upward and forward you can get your COM higher and further forward. By then driving the arms down and bending your hips and knees forward at the top of the jump, you keep your COM elevated allowing you to gain added distance before touching down. Lifting your arms arms/knees and bending hips raises your COM. We see that the first subject reaches his maximum height at a further distance than the second subject.For the second subject, it's difficult to anticipate whether he will land closer or farther than the first subject though, as his maximum height is a few inches higher.

Both subject 1 and subject 2 have not remained fully extended through the peak of their jumps and have started to rotate for the landing. Subject 1 has begun to lift his chest, while subject 2 has already dropped his arms and brought his knees forward. Keeping yourself extended, as long as possible, through the peak height of your jump will allow you to jump further. A body position midway between that of subject 1 and 2 would probably be ideal.

At the peak of the jump it is now time to start rotating your body to get your legs out in front of you. The distance of the broadjump is measured where your toes land, so upon reaching the top of the jump, you should get your legs out in front of you. To make this happen, drive your arms downward and bend your hips and knees up toward your chest. Do not lean back as subject one has began to do; it is better to bring your hips and knees up to your chest.

4. Landing
In order to land safely and get the most distance out of the jump, our subjects flex their hips and extend their legs, landing on their heels with their toes pointed upwards. The second subject lands with his torso bent forward a bit more; but besides this and the placement of their arms, the subjects' landing techniques look quite similar.

5. Finish
The broadjump distances were measured from the subjects’ starting toe positions to their final toe positions. In order to absorb the shock of their landings, it’s important that the subjects bend their knees through impact. We see that the first subject doesn’t flex his knees as much as the second subject, and as a result ends up falling forward a bit at the end of the trial. This shouldn’t matter much though, as the jump distance has already been measured and the purpose of the drill isn’t to work on the landing. However, if someone was performing additional movements at the end of the broadjump (some training camps have the athletes do three consecutive broadjumps and measure the overall distance), it’s recommended to have more of a controlled landing at the end of each jump.

We hope you’ve enjoyed this article, and that you’re getting out there and filming great videos of yourselves and your athletes for detailed analysis!

Kobe Bryant Perfect Trick Shot Mechanics

2009-11-23T09:10:00.000-08:00

Kobe Bryant is one of the three best players in the NBA. However, there can be no doubt that he makes more unbelievable and impossible shots than anyone still playing professionally on a basketball court

Take a look at this one from the LA Lakers Game against the Oklahoma City Thunder. There is no need to try and spot the trick, he is shooting over the backboard.

Kobe can make these incredible shots time after time, because of two important facts.

He practices making shots from almost anywhere on the court. To learn how to shoot the ball over the backboard , you need to try it and try it often. It may seem like a waste of time but professional athletes practice trick shots to give themselves more options on the field. Having a practiced trick up your sleeve also confuses your opponent who in the professional leagues has probably seen and knows how to defend the regular shots. Practicing trick shots happens in all sports. Take a look at Roger Federer and his trick shot winner at the US Open in 2009.
Practice is important, but what also makes this shot and many other of Kobe's trick shots possible is that he uses flawless shooting technique. Take a closer look at his mechanics in the video above as he shoots.

Kobe gets up in the air and squares his shoulders so that he is facing the net.
He keeps his elbow high.
He paints the ball with his hand, allowing the ball to roll off his fingers rather than pushing it toward the basket.
He shoots the ball on a high arc, taking advantage of the size of the basketball rim (2X the diameter of the ball).

Take a look at this video of Kobe shooting free throws. Notice that his arm mechanics here are pretty much the same as for the over the backboard shot against the thunder. Shoulders squared to the basket, elbow high, paints the ball with his hand and launches the ball on a high arc.

By using good mechanics for all his shots, Kobe is ready to try any trick shot at any time.

Henry Gives France a Hand into The World Cup

2009-11-19T10:12:00.000-08:00

Another week and another call for the use of video replay in sports.
This time from the football (soccer) World Cup qualifier between France and the Republic of Ireland.

Frances' William Gallas scores from an assist by team mate Thierry Henry. Replays and video evidence clearly show that Henry used his hand, intentionally, to control the ball before crossing it.

Watch the video below. Although I believe that Irish football commentary is often biased for their team, the commentary in this video is not biased. It is obvious that this goal should have been disallowed by the referee or the linesmen.

Henry admitted after the game that he had used his hand. I am not sure that any player with the desire to win this do or die World Cup qualification game would not have risked the same. I am sure he even expected the goal to be disallowed. Henry conned the referee and linesmen. Similar cases, particularly of players diving to win penalties, are prevalent in football at all levels and throughout the world. Players should never in my opinion deliberately try to con the referee. However I have no intention of passing judgement on Henry's character or that of any other professional athlete. This website is about video analysis, so once again we will harp back to a previous discussion on the use of technology and particularly video replay in sports.

In this particular instance we had some clear evidence of the hand ball from the TV footage. But again we need to point out that the evidence is not always that clear. See our previous post on video technology for refereeing. There have been numerous calls in soccer when the decision could have gone either way because of lack of clear video footage.

Watch this video of Wayne Rooney falling to win a penalty against Arsenal earlier this year. This decision is less obvious, was Rooney already falling or did the Arsenal goalkeeper touch his foot and bring him down? Was the ball close enough to be retrieved before going over the goal line? Even on watching the video it is a difficult decision to make.

The video technology in this case has let us down. A side on view of this same incident would have enabled us to better assess the position of the ball and the point at which Rooney begins to fall. We would also have been able to tell when Almunia, the Arsenal goalkeeper makes contact. So here is a decision that even with video replay remains controversial.

I believe that some amount of controversy actually brings excitement and emotion to the game. As a fan of a losing team, what better way to make yourself feel better than to suggest that the team would have won if the referee/player/coach/linesman hadn't cheated. In fact had Henry's goal for France been disallowed, Ireland would not have automatically won as many of the Irish believe (the score was 1-1 on aggregate before the goal went in), and may even have lost in the end anyway. Now just think of the great grudge match when France and Ireland meet again, even in sports other than soccer.

The problem is the blaming. With a referee in charge there are bound to be honest mistakes on occasion. Sometimes there may even be some blatant bias. The players too can make honest mistakes. A player falling over in the penalty box is not always trying to win a penalty, he may be trying to avoid injury.

Video replay technology can give increased accuracy to the decision. A referee is not always in the perfect position to make the most accurate call. Video from different angles can give the official added perspectives to help make his decision more accurate.

Video technology can remove all of this bias and simplify things. However it currently is not 100% accurate and controversial decisions will remain when the perfect camera angle is not available.

As technology progresses and even now with a good camera placement, such as those used in cricket and with the Hawk-Eye system for tennis, even more accurate decisions can be made.

It's time to bring in the video replay for all sports that rely on a referee or umpire to make a decision.

Football Quarterback Throws - The Long and Short Pass

2009-11-16T09:33:00.000-08:00

The NFL is becoming a very offensive game, with quarterbacks like Peyton Manning, Tom Brady and Phillip Rivers airing out long passes regularly and using short quick passes to their running backs more often than the hand off.

The reasons for the increased amount of passing in the NFL are still up for debate. The simple fact is that the teams whose quarterbacks are throwing more are winning more. If throwing is the winning formula then all teams are going to try it.

All this throwing makes for exciting football. Hail Mary passes for touch downs, miraculous interceptions and numerous spectacular catches have all been part of the 2009 season. The wide receivers have to be on their game and the quarterbacks have to throw accurate passes with the right amount of force , often under pressure.

The quarterback has two basic options when throwing a pass. He can either step into it and air it out for distance, or he can throw a short accurate pass.
In both cases it is important to use proper mechanics to achieve the results and also to prevent any injury to the shoulder or elbow.
In general the best mechanics for all throws can be described as:

Aim your non throwing shoulder at your target.
Step forward with the opposite foot to your throwing arm to counterbalance the throwing action.
Rotate your hips toward your target followed by your shoulders and finally your throwing arm.
Follow through with your throwing arm, so that you put speed on the ball and prevent injury.

Lets take a look at two different types of passes, by our two quarterbacks. These quarterbacks (myself and Dennis) are weekend flag football quarterbacks and do not have the best mechanics. Although we will comment on their mechanics (good and bad) we are focused on the differences between the two throws.

The first throw shows QB1 stepping into a throw and attempting to follow the mechanics described above. He is attempting a long throw to his wide receiver way down the field.

QB1 starts by taking a few steps back. Most quarterbacks do this to create some room to step into a throw. This is not always possible, but it is usually necessary if you are trying to throw to a wide receiver way down field.
He then does a little skip hop to position his back foot at right angles to the direction he wants to throw. He does this so that his hips also remain closed to the target (at right angles).
His lead shoulder (left) is also pointing toward the target. This also keeps his shoulders closed to the target.
The red arrow shows how QB1's hips will rotate toward the target, while the blue arrow shows his shoulders. Rotating first his hips followed by his shoulders toward the target will create a kinematic sequence which will allow QB1 to put more speed into his throw and therefore get more distance. The kinematic sequence was first described in golf but it can and should be used to create power in any throwing or hitting sport. The idea is that by first accelerating your hips, then shoulders then arm toward the target in the throw you will create the most energy for the throw with the most efficiency and least effort.
Our QB1 does not make best use of the kinematic sequence as his hips and shoulders rotate toward the target almost simultaneously, but he is still using his rotational energy to create throwing speed.
Finally he follows through with his arm across his body to obtain maximum speed until ball release and allowing his arm to decelerate after the throw.

Now lets look at QB2 , who is also stepping into a throw, but he is keeping his hips and shoulders open to the target and using mostly his arm to make the pass. With this technique it is very difficult to throw a long pass and is usually used in rushed situations and for short passes.

QB2 also takes a few steps back to create space. This is not necessary to throw a pass like this but it may give the quarterback some time to make a decision.
He also takes a skip hop but lands with his back foot facing toward the target. This keeps his hips open to the target.
His lead shoulder turns a little toward the target, but he cannot turn as much because he has kept his hips facing the target. Turning his front shoulder toward the target a little, allows QB2 to get a bit of rotation of the shoulders into his throw.
The red arrow describes the direction of QB2's hips moving forward and the blue arrow the direction of his shoulders. He is not using the kinematic sequence to create arm speed in this case. Although by turning his front shoulder a little toward the target, he is getting some of the energy of rotation that the kinematic sequence gives a thrower.
Unlike QB1, QB2 needs to use much more strength in his throwing shoulder and arm to throw his pass. For this reason it is very difficult to throw a long pass using this technique. If QB2 attempts to throw as hard as he can with this technique he could cause shoulder or elbow injuries, because of the extra stresses and forces on his muscles.
QB2 is meant to be throwing a short accurate pass, but he does release the ball a little early, so we will assume he was just trying to lob it over the defenders head.
Finally QB2 follows through across his body, allowing his arm to decelerate without injury.

Watch the quarterbacks in the NFL and notice when they throw with an open hip and shoulder technique and when they rotate toward the target. In most instances you will see that they use the kinematic sequence and rotate their hips and shoulders into the throw to create good accurate passes, even for short passes.

Once in a while however, usually when they are under pressure, you will see them launch a pass with hips and shoulder facing their receiver and using mostly their arm power and little rotation.

Enjoy the rest of the NFL season. We hope to see many more games with more than 300 yards passing. Get out your video camera and film your throwing mechanics to compare to the pros.

Analyzing Dane Reynolds in Slow Motion

2009-11-10T08:46:00.000-08:00

Sometimes it is simply fun to see a pro athlete perform in slow motion. Usually though we can learn a lot from watching him or her in such detail.

Surfing is one of those sports that lends itself well to photographs and video clips. The action is usually intense and the surfers positions so contorted that it is a wonder to see them perform. Of course because their movements are often quick and dynamic, it is difficult to analyze their motion at normal speed. Recently there have been attempts to analyze professional surfing from a scientific stand point of physiology and biomechanics. Check out a previous article we wrote about a trip to the Mentawai islands.

Recently the Quicksilver surfing team was in Mexico and took along a high speed vision research camera. This super slow motion camera can record at high resolution up to a frame rate of 7530 frames per second. We do not know the frame rate used to record this video clip, it is most likely at around 1000 fps. This does not sound like a lot when we consider that golf swings seen with the Swing Vision system are often recorded at 10X this frame rate. However it is generally accepted that the fastest movement that a human can make can be recorded at 250 fps, therefore a high speed capture at 1000 fps is 4X the fastest movement that the surfer can make. The reason Swing Vision uses a higher frame rate for golf is to capture the golf club and ball, which can move much faster than any part of the human body.

The video shows Dane Reynolds performing an aerial surfing move in Mexico, recorded by the Vision Research Camera.

Analyzing Dane's performance to learn how we can perform a similar move is easier because of the high speed footage. Lets take a look at some critical points.

Dane starts by balancing his center of mass (the center of all the masses and positions of all his limbs) between his feet, which are toward the back of the board. We can see that his weight is at the back of the board by noticing how the nose of the board is sticking up out of the water. We also see him leaning into the face of the wave so that he can turn quickly to launch into his aerial move.
Mid way up the face of the wave, Dane applies more pressure to his back foot, shifting his center of mass further back. We see his front knee straighten and his head lift up eyeing his take off point. The movement prepares him to almost jump off the wave with his back foot when he reaches the top.
At take off Dane pushes his back foot almost straight (jumping). He does this to launch the board into the air and also to bring it up closer to his hands so that he can grab it.
Once in the air, just off the wave we can see how Dane pushes the board around with his back foot, while bending his front knee. He also lifts his head up and forward as if he is trying to peer over the top of his board. This enables him to get the rotation needed to bring his body on top of his board so that he can set up for the landing. In fact it almost looks like he is climbing up his floating board with his hand.
Now that he is in the air and has got back on top of the board he needs to prepare for the landing. This time, unlike when he was riding the wave at the beginning, he positions his center of mass over the middle of the board. This will give him a bigger landing area. If he positioned himself over the back of the board as he did at the start, the board would most likely slip forward and out from under him on landing.
On landing he stretches out his legs to reach for the top of the wave and then allows them to bend to absorb the landing impact. Notice how his arms are in an equal and opposite balancing position over the center of his board to keep his weight centered.
Interestingly on his landing we can see the flex or wobble of the board itself, which probably gives him a little more shock absorption.
Finally riding out we can see that Dane's body is leaning backward a little and the board is sliding out forward. This is probably a result of his not having his center of mass directly over the center of the board at landing. However Dane quickly recovers by bending his knees and moving his arms forward to once again position himself over the center of the board and ride out.

Breaking down a movement using high speed video footage can be very instructive. If you are a surfer, we hope you were able to pick up a few tips. If you are not a surfer, take a look around for high speed video footage of your sports and see what you can learn from the pros. If you have any suggestions of high speed video you would like us to analyze let us know. We enjoy hearing your comments.

Using Video Overlay to Compare Two Athletes' Shuttle Runs

2009-11-03T14:20:00.001-08:00

A shuttle run is often used in professional sports combines to determine the fitness of a prospective athlete. A shuttle run consists of an athlete running back and forth between two lines approximately 30 feet apart, touching each line before heading back the other direction. The videos below were taken at a basketball court that already has a series of lines marked out. We used those lines to mark the beginning and end points of the run, rather than measuring out 30 feet.

This exercise is a way to evaluate an athlete's speed, quickness, and agility. According to the National Academy of Sports Medicine, “speed” is defined as the ability to move the body in one intended direction as fast as possible, “quickness” is the ability to react and change body position with maximum rate of force production, in all planes or directions of motion, from all body positions, during functional activities, and “agility” is the ability to accelerate, decelerate, stabilize, and change direction quickly, while maintaining proper posture.

Most testing sites simply use the athlete’s overall time as a way to make this evaluation, as shown in the first two parts of the video below (the first subject recorded a time of 10.377 seconds, and the second subject recorded a time of 10.010 seconds). But knowing the overall times only tells us which subject completed the trial the fastest, not why or how one was faster. In this week’s article, I’d like to discuss the value of using the video overlay feature to determine the point or points in the run where one subject gains an advantage over the other.

Video overlay can be used for a wide variety of comparisons. For example, it can be used to compare:
• A single athlete, before and after training (as a way to determine the effectiveness of training)
• A single athlete, before and after rehab.
• Multiple athletes

Video overlay and athlete comparison works best when the subjects are moving from left to right, or right to left,(sagittal plane) across the camera’s view, as it’s much easier to view when the separation between the athletes occurs during the trials. During the 2009 NFL combine, the television coverage tried to use this technology for the 40 yard dash, but they overlaid too many athletes’ trials (10 or more) on top of each other; and since there was very little difference in the athletes’ times, the end video looked like a bit of a mess. Therefore if you plan to use video overlay to compare athletes, don’t overlay more than two or three subjects at the same time.

To make things interesting for our recordings, we chose to make each shuttle run turn facing the camera, so there are two right turns and one left turn in each trial.

Take a look at the third part of the video (showing the overlaid athletes), to see where the separation between these two subjects occurs.

We see that the subject in the gray shirt (we’ll call him Subject 2) gets off to a slightly faster start than Subject 1 (blue shirt), and reaches the far cone first. After making this right turn, the distance between the subjects remains the same until they return to the starting cone, so we can assume they both came out of the first right turn in the same amount of time, and that they ran with the same speed between the far cone and the starting cone. Coming out of the left turn, Subject 2 starts to break away a little more, so it’s possible he is faster pivoting off his left leg. And after making the final right turn, the distance between the two subjects remains about the same after the left turn through the finish.

So what were the turning points in this race? It seems Subject 2 got off to a faster start, and was quicker coming out of the left turn; so it may be useful for Subject 1 to work on his start (see http://videosportsanalysis.blogspot.com/2009/08/video-analysis-of-sprinting-from-start.html for details on how to start fast)> We also see that Subject 1 lost some time in his second turn and acceleration from there. He may also work on strengthening his left leg, to help him make the left turn a bit faster. We also happen to know that Subject 1 has had rehab on his left knee in the past and therefore may have a weakness or instability that still needs work.

By using the overlaid video, we were able to get a lot more information about these trials than just who finished first, and can use this information to make specific recomendations to an athlete's training regimen or to assess the rehabilitation of an athletes injury.

As you can see video overlay can be a powerful tool when evaluating an athlete’s performance. We value your comments and would be happy to answer any questions.

Replay Technology Will NOT make 100% Correct Calls

2009-10-30T18:00:00.000-07:00

More blown calls in a major sporting event. This time in the 2nd game of the Major League Baseball World Series, between the New York Yankees and the Philadelphia Phillies. Chase Utley of the Phillies was called out at first base, when video evidence suggested he had touched the base before the ball hit Mark Teixeira’s glove. In the same game Ryan Howard was judged to have caught out Johnny Damon, when the ball looked to bounce before hitting his glove. There have been a number of poor calls in this seasons MLB playoffs once again, and blown calls are happening in numerous other sports, including soccer and tennis.

The technology of high definition and high speed video of today can easily eliminate many of these blown calls. Sure there is the argument that using video replay can slow down the game. In baseball in particular this would be truly frustrating, but we would I think all prefer to see the right call made most of the time, particularly in big games such as the World Series.

Cricket is a great example of where camera technology is used to good effect. The cameras are setup side on to the crease (batters line) and can see both the wickets and the crease. In most cases just this one camera would be enough to determine the position of the batter as well as whether the wickets bails had been dislodged. If the umpire on the field is unsure of a run out situation, he will refer the decision to the camera technology, or the 3rd umpire, who will make a definitive decision after reviewing the video footage.

Although we definitely support the use of video analysis to assist umpires and referees, it is important that everyone; umpires, athletes and fans understand that even with video analysis a call can not be 100% correct every time.
Video footage cannot always capture the event from the correct angle or the video cannot be slowed down sufficiently to determine some calls. The fact is that the video footage may not show enough evidence to support or over rule a call.

Fans in particular make the mistake of believing that video evidence will always be able to determine whether a call is correct. Unfortunately this is not the case.
If the camera reviewing a line call or judgement does not have a direct view, then the video image may not help to determine the accuracy of the umpire's call. When close calls are viewed from an angle given by a television camera, they can sometimes give misleading evidence of the accuracy of the call. This can be particularly problematic for example, when using one camera angle to determine whether a base runner has been thrown out. The base runner is running between the bases and the camera could be setup at a good angle to view when the runner touches the base. However, and here is the problem, the ball may be thrown in to the fielder from anywhere on the field (this cannot be determined in advance), therefore the camera setup to view the runner may not be in the best position to accurately determine when the fielder caught the ball and it will be possible for incorrect judgements to be made. If on the other hand we have a great view of the fielders glove and ball, we may have the incorrect perspective of the base runner and when he touches the base.

Of course these 2 situations did not take place in the 2nd game of the MLB World Series, but they also cannot be discounted.

Take a look at the 2 photographs below.

In the above pic we have the view from one camera and shoe looks like it is on the edge of the mat.
Now lets take a look from a second camera with a better view of the edge of the mat and the shoe.

Of course it is pretty obvious from this camera angle that the shoe is just short of touching the mat.
From this we can see that the incorrect camera angle could result in an incorrect call.

The problem of incorrect camera angle could be solved by having multiple cameras, all synchronized with a time source and calibrated so that the 3D position of the ball can be determined. This is how the Hawk-Eye system for Cricket and the Tennis challenge system works. Beside the fact that this type of technology requires numerous cameras, can be very expensive and requires processing time before a decision can be made, it too can suffer from inaccuracies when the ball or target being tracked is hidden from the view of a number of cameras. This can often be the case when their are numerous players on the field, or the lighting is not ideal.

So we know that video analysis of umpiring and refereeing decisions are not 100% accurate. In fact the Hawk-Eye system claims they have an accuracy of 3.6mm. This means that the ball can miss the line by 3.6mm in Tennis and still be called in by the system. In NFL football when a call is challenged and a review takes place, often the result suggests that there is insufficient evidence and the call on the field cannot be over ruled. This insufficient evidence occurs because the camera cannot get the best view of the ball and its position because of the scrum of players or a camera angle that is not optimal.

The umpire or referee has a distinct disadvantage to technology. He or she only gets one chance to get it right. If they fail to get into the best position, have the best view of the play, find the best perspective to catch all the action and happen to blink at the critical point, they could easily make the wrong call.
The camera even with the possible errors in perspective or lighting and the small errors with 3D tracking , can capture high resolution and high speed footage and replay it over and over again.
This advantage will ensure that technology will get the call right more often than even the best and luckiest umpires and referees and should be used whenever an umpire is unsure of the call to be made.

A final thought. While we wait for technology to be used, we should remember that even video footage could result in incorrect decisions. There will always be some statistical error, only a lessor error than those made by human umpires. Fortunately with technology, line calls can not be biased by emotion but only based on whatever video footage is available. With this technology even the teams we support will catch a few breaks in the long run.

Table Tennis BackHand TopSpin

2009-10-27T07:39:00.000-07:00

Table Tennis, which is sometimes known as "Ping Pong" in the USA is a dynamic sport requiring fast reactions from its players. A professional and skilled player is able to impart various types of spin to the ball, to keep their opponent on the defense and limit their options.

The backhand topspin shot is just one way to impart spin. Below is a great video describing the technique needed to hit a good shot both across the table and down the line.

This video is a fantastic example of using video footage to analyze motion. The camera is setup directly in front of the table tennis player so that we can see well how he changes his stance and hits the backhand topspin shot.

Table tennis is great exercise and fun to play. Learning a few different shots by watching and analyzing video, will help you enjoy the game even more.

Disguising your Baseball Pitch Like CC Sabathia

2009-10-19T07:29:00.000-07:00

The Major League Baseball post season is nearing an end. The League Championship series are in full swing with two great match ups. The Los Angeles Dodgers are taking on the Philadelphia Phillies and the Los Angeles Angels have the formidable task of attempting to overcome the New York Yankees.

Baseball particularly in the post season is dominated by the pitching. Great batters are successful only around 30% of the times they come up to bat but great pitchers on the other hand can dominate and beat the batter 80% of the time. A great pitcher needs to be able to throw a variety of balls, so that he can beat any batter and can throw to the batters weakness.

There are 3 pitch varieties, the fastball, breaking ball (slider or curve ball) and the change up.
The pitcher must then be able to throw each of the 3 pitches listed above to hit 4 different targets: high inside and outside and low inside and outside.
The pitcher also needs to understand the batter he is up against, his strengths and weaknesses. Is he left or right handed? Does he have an open or closed batting stance?What did the batter do on his previous at bat?
Finally the pitcher also needs to throw pitches according to the pitch count. This is often called pitch strategy. The pitch strategy will change as the number of strikes and or balls change. For a detailed description of pitch strategy have a look at this article by Tom House.

In the first game of the American League Championship final between the Angels and Yankees , we watched CC Sabathia of the Yankees put in an excellent display of pitching. He pitched to all corners of the plate and varied his pitches with the pitch count and player.

Below is some video of Sabathia pitching strikes to the Oakland A's in August this year. Watch for the variety of his pitches, fastballs, breaking balls and change ups, as well as the numerous targets he hits, inside and outside, high and low, to both right and left handed batters.

Sabathia is one of the best in the MLB this year and his ability to pitch a variety of pitches is one of the main reasons for this.

However it is also important when throwing these different pitches that the player is able to disguise the type of pitch he is going to throw. If the pitch is well disguised it gives the batter less time to react to the pitch and reduces their chances of getting a hit.

Lets look at the video of Sabathia again. Notice that his action is always the same for every pitch, whether it is a fastball or a slider, whether he throws high or low. Focus on Sabathia only as you watch the video.

Sabathia covers the ball with his glove at the start of every pitch.
He rotates his shoulders back the same amount each time. He also lifts his front knee to the same height on every pitch.
He seems to stride forward to almost the same position on each pitch.
His arm comes through at the same speed and height for all his pitches. Most of the pitches he throws in the video above are in the 83-84 mph range, but the 2 faster pitches 88 and 97 mph look very similar to the others.
His follow through for all pitches also looks the same. His head remains looking up and forward.
He even completes the routine after the pitch in the same way by pulling up his shirt sleeve.

We all know from our experience that the video above is not the best for analyzing Sabathia's technique or timing. The best footage would be from the batters perspective, but from the angle we have, it certainly looks like each pitch is very similar. If the batter is able to read the pitchers mechanics and guess at the pitch to be thrown, he will have that little bit more time to modify his swing and get a hit. By throwing different pitches using the same technique and timing, Sabathia is able to delay the batters decision to swing and therefore is able to beat them more often.

The best technique for throwing all types of pitches is the same, there should be no need to vary your technique to throw a different type of pitch. To throw a curve ball, slider or any other type of pitch the variation is in the grip and in the final position and snap of the wrist, not the pitching mechanics.

To pitch like CC Sabathia, concentrate on the pitching mechanics. Fool the batter by showing him or her the same mechanics on every pitch. We will follow up with a video analysis of good pitching mechanics soon. In the mean time enjoy the post season and World Series. Keep an eye out for Sabathia and see if you can spot any variations in his mechanics with each pitch.

Wearable cameras for Sports Video Analysis

2009-10-16T08:42:00.000-07:00

The Motion Capture technology company Vicon, announced yesterday that they had signed a license with Microsoft to develop a wearable camera based on the Microsoft SenseCam technology. The camera will automatically take pictures and I assume video for the wearer as they go about their daily activities.

Of course the camera has some immediate benefits to dementia and Alzheimers sufferers. The camera images will help these patients to create visual memories of activities during the day. The camera will also have application in patient monitoring, allowing Dr's to evaluate patients well being or compliance with a treatment protocol.

The articles on this website are about sports analysis though, and I believe that the Vicon Revue camera (the name for this new camera) will have benefits for sports performance too. Of course there are already cameras available that can be mounted to a helmet or some sports equipment and enable the sports activity to be viewed from a first person perspective.

Here is a great video using a helmet mounted video on a mountain bike.

So how can we use a wearable camera for analyzing sports performance. Here are a few suggestions that I think would be useful.

As we saw in the video above, the camera was mounted on top of the bikers helmet. A camera mounted on the helmet can help us to analyze head movement during the activity. Most sports require the head to be still during a particular motion. The head, with the skull and brain has a lot of weight for its size. Moving your head around during a sports performance can often throw you off balance.
The helmet mounted camera can also help analyze what we are looking at during the activity. For ball sports such as baseball, cricket, tennis and golf, the position of the head often determines how you will hit the ball. Lift your head too early during a golf swing and you may even miss the ball completely.
A wearable camera may also allow you to analyze your positioning in team sports. If you are a defender in soccer, the camera can assist in analyzing how close you were able to stay to your assigned mark.
A wearable camera may provide excellent feedback to a coach during a game. A player wearing the camera can provide the coach with important information about the oppositions positioning on the field.

Although video cameras are getting smaller everyday (the Vicon Revue is smaller and lighter than an ipod) , wearable cameras will probably need to get even smaller still before they can be used effectively in a competitive sporting arena or for that matter as a coaching tool. For the moment cameras can only be mounted on helmets or sports equipment and not all sports use suitable equipment.

Once cameras become small enough to be sewn into the badge of an athlete's jersey we may see many more application for first person, wearable, sports video analysis.

Big Hitting Cricket in Twenty20

2009-10-13T00:30:00.000-07:00

Visiting South Africa this month I had the opportunity to watch live cricket once again. I always enjoyed cricket, but it is difficult to watch international matches while living in the USA.

I had the opportunity to watch some ICC Championship 50 over cricket and then some of the Champions League Twenty20 cricket being played in India.
Twenty20 cricket is a highly explosive form of the game which is bringing great excitement to the cricket world. The Twenty20 game allows each team only 20 overs of 6 deliveries each to make a total. This means that the batters need to make runs quickly and hit big shots off every ball. They cannot afford to miss or get no run from a shot. You can find more details on the laws of Twenty20 cricket here.

As I watched the Champions League Twenty20 cricket and some big innings from the likes of JP Duminy and Jacques Kallis, I thought it would be fun to look back at a 2007 World Championship game between India and England in which Yuvraj Singh of India, hits a six (the most runs you can get for one shot) off each ball of the over. A six is hit when the ball is hit through the air and carries over the boundry rope on the perimeter of the field. To hit a six the batter needs to hit the ball hard and high. Six spectacular sixes in one over for 36 runs. Check out the video below.

High Speed Sports Video on TV

2009-10-05T06:30:00.000-07:00

We all already have or want that high definition plasma, LCD or even better, LED television. If you have watched sports on high definition TV, you know the difference immediately. The players are recognizable. No more asking who made that tackle or scored that goal?

Now a number of TV sports programs also show high speed replays, with the most prominent example being CBS Sports Swing Vision, which is used for CBS Golf coverage as well as Tennis and numerous other sports. We also see high speed video being used on TV and in sports to help make critical refereeing or umpiring decisions, such as the Hawk-Eye system for Tennis line calling and for the LBW decision in Cricket and high speed video replays for NFL challenge decisions.

Obviously there is a difference between high definition (or high resolution) and high speed video.
Normal TV images have up to 576 vertical lines of pixel data and the video is recorded at either 24 or 30 frames per second, depending on whether you are in Europe and Africa or in the Americas and Asia. The 576 lines describes the resolution or standard definition, while the 30 frames per second describes the speed of playback. Now your high definition television may have a resolution of 1080 progressive (1920x1080 or 2.07 MPixels) but the TV program you are watching is often recorded at the same frame rate as your standard definition TV, 24 or 30 frames per second. These days as more people have high definition TV's that can play back the higher frame rates, there are more sports broadcasts being filmed at 60 frames per second or even a little higher. This however is still not high speed video.

Therefore you can see that high definition television does not necessarily mean that we can always see slow motion replays of high speed motion. Special high speed cameras are needed to record broadcast quality high speed images such as those seen with swing vision.

High speed slow motion replays require cameras that record video data at 500, 1000 or 2000 frames per second and sometimes even higher. At the same time, they need to record with resolutions as high as 1080p, to retain their broadcast quality.

Swing Vision claims to record high speed footage with frame rates up to 40,000 frames per second. It is certainly possible for high speed cameras these days to record video at 1920x1080 pixel resolution at speeds of 2000 frames per second. To get higher speeds of capture broadcasters can trade in some of the resolution and for example record at 1280x720 pixel resolution (still HD) at 10,000 frames per second.

Below are 2 examples showing a HD video of surfing recorded at normal frame rate and played back in slow motion and a HD video of surfing recorded with a high frame rate and played back in slow motion.

If you pause the first video at any stage you will notice that the image goes a little out of focus. So although this video was filmed in HD, it was not filmed with a high frame rate. The fast motion of the surfer causes the paused video image to blur a little as her frequency of movement is faster than the frame rate of the camera.

The second video was recorded with the Typhoon HD4 high speed camera which can record video at 1280X1024 pixel resolution (1024 HD) at 1000 frames per second for full resolution. If you pause this video you will notice the clarity of the image. The surfer and wave frequency of movement is slower the camera frame rate.

We can see the difference between HD video of sport recorded at normal speed and high speed. The high speed recording allows for much more clarity in viewing high speed movement and therefore the chance to analyze performance in much more detail. In these surfing videos, you are probably thinking that the higher speed camera was not necessary to analyze the surfers movement as the clarity of the first video was more than enough. This is true but for higher speed movement such as the club during a golf swing, the higher frame rate can help identify those small improvements that can make a difference.

When capturing video of your own performance you may not be able to afford or for that matter need a high definition, high speed camera. Human movement, even fast human movement is predicted to have a maximum frequency of around 250 hertz. This suggests that even for the fastest human movement (not including equipment such as the golf club or tenis racket, which will move faster) 250 frames per second capture speed will be enough. But, the higher the frame rate you can get on your camera the more detail you will have to analyze in your video. There are numerous HD video cameras available and many of them can record at 60 frames per second and some even higher. To analyze your performance this is a great place to start.

Video Analysis of a Bench Press

2009-09-29T10:25:00.000-07:00

This week University of Southern California football running back, Stafon Johnson, was bench pressing during training when the bar slipped out of his hands and landed on his throat causing severe laryngeal as well as neck injuries.

The bench press is a great exercise to build your pectoral (chest), triceps, biceps and deltoids (main shoulder) muscles. The exercise is used in training for many athletes in numerous sports, but especially in football. Johnson therefore would have bench pressed numerous times before and also had a coach or fellow athlete spotting him at the time of the accident. I am sure Johnson was using good technique and the accident was very unfortunate rather than a mistake on the athlete or trainers part. In most cases when a the bar slips during bench press it lands on the chest and causes much less damage. According to his doctor, Johnson should make a full recovery.

However it is important to understand that the use proper technique can help athletes avoid injuries such as tendon or muscle tears as well as build the muscles more effectively.

Below is a video of strongman Derek Poundstone from the USA bench pressing 500lb. Lets take a look at his technique.

Before we begin to analyze this video remember that when doing the bench press, always have a spotter, someone to help steady the bar or pull it up if you need it. We can see Derek's spotter watching carefully as he bench presses. It is also important to start with a low weight and test your ability before increasing the weight. very few athletes can bench press anywhere near 500 lbs. So start low, even if the bar is too low weight, you can always add more.

So here are some key points to note in the video above:

Derek lays down under the bar and bends his knees drawing his feet up and pressing them into the floor. In doing this he creates a support base for his bench press and he is able to use his quadriceps (leg muscles on the front of his legs) to control his body and balance the bar. If he did not anchor his feet his body would be like a fulcrum with too much weight near the head and he would strain to balance the bar.
Derek's spotter helps him to lift the bar off the supports and align the bar directly over his shoulders. He therefore can lower and push the bar straight down and up, with little angle. This will ensure that he works the appropriate muscles to their full extent and avoids injuries that may be caused by using muscle force to push at an angle that would put excess and inappropriate strain on the muscles or joints.
He lowers the bar straight down to his chest, just below the nipples (the bottom of the yellow image on his shirt). Once again this ensures that his arms lower the bar straight down and push it straight back up.
Finally Derek's spotter assists him in replacing the bar correctly. This is possibly where Stafon Johnson slipped and how the bar could have landed on his neck. You will see that Derek looks to make sure that the bar is properly supported on the hooks on both side of the support before relaxing and letting the bar go.

Before you start bench pressing, determine whether your goal is muscle mass or explosive power. You can build muscle mass with high weight and low repetitions or build explosive power by pressing a lower weight but increasing the number of repetitions. Whatever your goal is for doing the bench press, remember to use proper technique and spotter at all times.

The Straight Drive in Cricket

2009-09-21T15:49:00.000-07:00

Batting in cricket is altogether different from batting in baseball in both objective and technique as well as the bat itself. In cricket the batter can hit or play at and miss as many of the balls bowled as he or she wants with a flat faced bat and scores by running between wickets or hitting the ball over the boundary. In baseball, it is 3 strikes and you are out and home runs or base hits, hit with a rounded bat, are the goal.

In both sport, professional bowlers or pitchers can deliver the ball at around 100 miles per hour and therefore timing and reaction are very important. In cricket though the batter can play a shot anywhere on the oval field, even behind him as long as he does not get caught or run out (I will not go into the rules of cricket but you can find them here). This means that in cricket there are a large variety of shots that can be played that require exceptional timing as well as perfect technique.

One of the classic and most eye catching shots in cricket is the straight drive. Most of the best cricket batters in the world such as Jacques Kallis and Ricky Ponting play this shot with ease and little effort.

Here is some video of Sachin Tendulkar, another cricket batting legend playing some straight drives off one of the fastest bowlers around, Brett Lee. The first shot is slightly mistimed and the ball angles off his bat, but the next 2 shots are perfect examples of a straight drive.

His timing and technique in the second shot is perfect and therefore requires little effort to transfer power and speed to the ball so that it races along the ground to the boundary and 4 more runs.

Let's analyze the video and break down his technique:

Tendulkar starts his movement by stepping with his front foot toward where the ball will bounce on the pitch and lifting his bat. As the ball is coming toward him at around 145 km/hr, he has very little time to react and therefore must move toward the ball and plan the shot he will play at the same time.
As bowling in cricket requires the ball to bounce, it can change direction and speed quite a bit after the bounce. Stepping forward to the area in which the ball will bounce allows the batter to get closer to the bounce and reduce the amount of movement that can occur after the bounce. This also allows the batter to get over the ball and prevent the shot from flying through the air and giving one of the fielders a chance to catch it.
Tendulkar brings his bat down straight with the flat face of the bat directed at the ball. Angling the bat will force the ball off in the direction toward which the bat is angled and also increases the chances of catching the edge of the bat or missing the ball completely. Although batters do sometimes play shots by changing the angle of the bat, you will not play a good straight drive with an angled bat.
Tendulkar connects with the ball around 1:21. By pausing the video you will see that his bat is alongside his front leg at the point of contact. His weight is also forward and over the front leg. He does this so that he can hit the ball directly toward the ground giving no chance for a catch. This timing also ensures that he has perfect balance and control over the shot.
He keeps his head down looking at the ball being hit off his bat and continues to keep his head down as he begins his follow through. Just as in other sports (golf, rugby place kicking) this helps him to maintain his balance through the shot and once again to keep the ball from lifting into the air.
Tendulkar then continues to follow through keeping the flat part of the bat facing in the direction he hit the ball and bringing his arms all the way above his head. This ensures that he hits straight and all the way through the ball.

The results of this perfect timing and technique are obvious as the ball flies off to the boundary and 4 more runs for Tendulkar.

The 2009 ICC Champions Trophy begins September 22 and the likes of Jacques Kallis and Ricky Ponting and Sachin Tendulkar will be showing off their batting prowess and often flawless technique from which we can learn.

The Skateboard Ollie

2009-09-17T15:04:00.000-07:00

Skateboarding has taken off as a sport over the last decade and the tricks being performed are often incredible. To perfect these tricks skateboarders spend hours practicing and falling over and over again.

Video analysis is the perfect tool to learn how to do skateboard tricks. If you are learning a trick that someone else has already perfected you have the advantage of watching them do the trick and learning from them. You can also get video of yourself performing the trick and compare your technique to theirs.

Another benefit is that it is easy to setup a camera to get the best view for analyzing the video. Because most tricks are done over a defined area and in a specific direction, you can easily setup a camera to get the best field of view and angle to analyze the trick.

One of the more basic skateboarding tricks is the "Ollie" (jump). The Ollie is the basis for most aerial tricks in skateboarding and therefore it is important to learn how to do a great one.

Here is a really good video with a lesson on how to do an ollie. The video of the ollie itself is excellent because the camera is setup well and looking directly at the skateboard and movement and not at an angle.

The video gives a comprehensive description of how its done. We can get some other tips from analyzing the video more closely.

At the beginning of the ollie, the rider applies pressure to the tail of board. He does this to force the front of the board up into the air to start the movement. However if he only applied pressure to the tail he would simply fall off the back of the board. Watch how he also maintains his weight over his front foot so that the front of the board will only move up as he lifts and shifts his front foot.
Coming to the take off, the rider jumps up into the air but notice that he does not use his arms to jump. The idea with an ollie is to stay connected or at least close to your skateboard throughout the trick. If you use your arms to jump, you may jump too high above your board and end up having a long way to fall back onto your skateboard.
The rider in the video also lets us know that to make your ollie higher you "suck your knees up to your chest after you have jumped". This helps you to raise your center of mass and of course the height of your feet and therefore allows the board to lift higher into the air. Your center of mass is the center of all the limbs of your body, and is usually somewhere around your navel. You can move your center of mass by moving limbs. Therefore if you raise your arms you raise your center of mass. If you jump and lift your knees up higher you will also raise your center of mass.
Your center of mass is also important for maintaining your balance when landing the ollie. In the video note how the skaters right arm ends up behind him on the landing while his left arm is in front. He is balancing his center of mass over the center of the skateboard by opposite and equal balance of his arms. This does not mean that you need to have your right arm back and left arm forward when landing your ollie, but you should be aware that you need to balance your weight over the center of the skateboard (both forward and back as well as left and right) so that you do not fall off on landing.

Good luck with learning to do an ollie. You can try practicing your ollie first on grass or softer ground before moving to the cement. Remember to also wear a helmet, all the pros do.

Federer Practices his Between the Legs Shot!

2009-09-14T09:41:00.000-07:00

If you were watching the US Open Men's Semifinal between Roger Federer and Novack Djokovic, you most likely saw Federer's incredible between the legs winner.

If not here it is:

Although we have video and some great angles, I am not sure that I am ready to analyze this shot. It is simply incredible. However, Federer said in the post match interview that he does sometimes practice the between the legs shot. We have also seen him use it before in match play, but never with such great power and precision.

Great players and athletes in any sport analyze and practice their technique all the time. They use video regularly to help them understand how to make improvements. Remember that all you need is a video camera and some basic understanding to analyze your own performances using video. Follow us here and look back through our previous posts to learn some tips and tricks for video analysis.

Video Analysis of Rugby Place Kicking

2009-09-11T09:17:00.001-07:00

Great kicking in rugby can make the difference in close matches. In 1995 Joel Stransky kicked South Africa to the Rugby Union World Championships and in 2003 Jonny Wilkinson used his kicking boot to drive England to its first Rugby Union World Championships.

In Rugby Union in the past, penalty kicks of more than 50 meters were seldom, if ever attempted, but now the likes of Dan Carter and Francois Steyn are regularly scoring points with penalty kicks from as far out as 60 meters. The players may be be fitter and stronger now than ever before, but they also kick better and further because they study and improve their technique using video.

Lets take a look at some video of Dan Carter practising his kicks and break it down a bit:

Dan is obviously a left footed kicker, so note that he approaches the ball at an angle (about 45 degrees from the target) from the right . You will notice that right footed kickers will approach at a similar angle from the left. The reason for this angled approach is to open up the hips and allow the hips and then the legs to swing through a larger arc and therefore create more power for the kick. We have talked about the Kinematic Sequence for the upper body before when discussing golf, tennis serves, baseball hitting and hockey slapshots. Kicking requires the same sequence but of course now we want to accelerate the hips, leg and then foot in sequence to kick the ball with power.
Carter does not take too many steps before the kick ( 3 to be exact). Most good kickers will take fewer steps to eliminate the possibility of not being in exactly the right position to take the kick. If you attempt to run up further there is a chance you will take a small or big step along the way and be out of position for the kick.
Dan plants his right foot just adjacent (next to the ball). If he placed this standing leg behind the ball it would force his kicking foot further under the ball forcing the ball higher in to the air but getting less distance. Alternatively if he overran the ball, placing his support leg past the ball he would not be able to swing his leg through and get under the ball sufficiently to get the distance required.
His hips, leg and foot kick through the ball in sequence. If you pause the video you will notice how his hips rotate through toward the target first and his knee is left bent behind. The knee then straightens out and brings the foot through the ball toward the target.
He keeps his head down over the ball as he kicks. Keeping your head down looking at the ball ensures that you are balanced for the kick and that you strike the ball cleanly.
Finally he follows through with his hips and kicking leg. You will need to pause the video just after the kick to see this clearly. Note also that his head stays down through the follow through, once again ensuring that he maintains his balance.

In the video we can also see that Carter rolls over his support ankle (right foot) during the follow through. This happens because of his angle of approach toward the ball, which I have suggested allows him to get a bigger swing at the ball. Although this looks dangerous , the roll is forced by his follow through when most of his weight has been lifted from the support leg. You will see that some kickers look like their support leg is lifting into the air, rather than rolling, with the force of the follow through and as their weight is lifted from this leg.

This weekend South Africa takes on New Zealand in a match that could be crucial in deciding the 2009 Tri-Nations champions. We will see Dan Carter and Francois Steyn in action and most likely kicking some big goals. I am originally from South Africa so I will just say it.
Go Bokke!

Mastering the Drop Shot in Tennis

2009-09-08T08:33:00.000-07:00

As the 2009 US Open continues, the top 4 ranked players, Roger Federer, Andy Murray, Rafael Nadal and Novack Djokovic are all still in with a chance of winning. To win against the likes of these Tennis greats, the players have to have a complete play list of different shots. One of the most lethal is the drop shot. Federer in particular loves the drop shot as a major attacking weapon.

The drop shot can be used to win a point outright, but it can also be used to draw your opponent to the net and set yourself up for a passing shot or to simply get your opponent winded by making them run up to net in an attempt to recover the point. Playing a good drop shot requires not only executing the shot itself but also determining the best time to execute the shot.

Here is some video of Federer with some sublime drop shots. As you watch the video take note of Roger's court position, how he swings the racket and the court position of his opponent in each case.

We can pick out a few tips from analyzing this video.

Federer usually plays his drop shot when he is just on the baseline or somewhere between the service line and the base line. It is much more difficult to play the shot when you are way behind the baseline. This is because the ball will need to travel further and it will also give your opponent more time to get to the net to hit a return shot.
His opponent in each point is usually way behind the baseline when the drop shot is played. His opponents therefore need to cover much more ground if they want to catch up to the shot.
Points 1 and 2 above actually work in combination, because as one player begins to attack , he moves forward and plays close to the baseline, pushing his opponent further behind the baseline. Therefore a drop shot is seldom played as a defensive shot.
In each shot Federer cuts under the ball to create backspin. He angles his racket and slices under the ball as if he is trying to chop the bottom of the ball off. Back spin ensure that the ball dies (does not bounce high or forward) once it lands on the other side of the net. This will further reduce the chances of his opponent reaching the shot. Cutting under the ball will also slow the flight of the ball down allowing it to drop closer to the net.

Roger has a great drop shot but he is successful with it because he knows when to play it. Using video analysis we can learn from Roger and practice incorporating the drop shot into our own games.

How Accurate is the Hawk-Eye System for Tennis Line Calls

2009-09-03T09:42:00.000-07:00

The US Open Tennis 2009 is in full swing. Once again the likes of Federer, Nadal and Murray are playing well and the men's championships looks set for an exciting second week.
We know and have seen how video analysis can be used to analyze a tennis players performance, but it can also be used in real time or almost real time to track the ball and even make close line calls. Of course I am talking about the "Shot Spot" or Hawk-Eye system.

If you have watched any Major Tennis since 2006, you will know exactly what Hawk-Eye is. The Hawk-Eye is used to make decisions on line calls that are challenged by the tennis player. Each player (or team if playing doubles) can challenge a line call on any point. They get a maximum of 2 incorrect challenges each set. If the set goes to a tie break an extra challenge is allowed. Basically the Hawk-Eye challenge enables the tennis players to use technology to challenge line calls they think are incorrect.

The technology being used by the Hawk-Eye system is Video Analysis. Here is how it works.

Multiple cameras are placed around the court and players. These cameras are usually placed high up, so that there is less chance that a player will be blocking the ball from the camera view.
Multiple cameras are used to ensure accuracy of tracking the ball and to account for possible occlusion (the ball being hidden from the camera view by the players body...)
The system uses at least 4 high speed video cameras, with a capture rate presumed to be 500 frames per second.
The camera position is calibrated to determine its position in space and relative to the other cameras in the system. The lines on the court are also used in calibration and to compensate for any camera movement.
The center of the ball is tracked in 2D by each camera. The ball therefore is like a reflective marker or point on the body. Using the information from all the cameras, the Hawk-Eye system then triangulates the 3D position of the ball.
This process is done for each captured frame so that a trajectory of the ball can be created and then overlayed on an animated background containing the lines of the tennis court.
Finally the skid and compression of the ball is measured by examining the position and trajectory of the ball prior to the bounce and its position and trajectory after the bounce. In this way they can determine how long the ball was on the ground and how it skidded over the ground.
The Hawk-Eye system is said to have an accuracy of 3.6 mm.

I believe that the use of video technology in this way is great for the sport of tennis and for the players piece of mind as well as spectator enjoyment. However we have seen a number of controversial calls with the Hawk-Eye system. Take a look at video of 2 big ones here.

In this first video we see a very tight call for Mikhail Youzhny over Rafael Nadal at Dubai in 2007.

This second video is from the Wimbledon final in 2007. Rafael Nadal benefiting from a very close one over Roger Federer.

In both cases we would have to say that the ball likely looked out to the lines judge who made the call. In both cases the player is most likely only challenging the call because it is a crucial point (Yozhny vs Nadal - Set Point, Nadal vs Federer - Break point). The Hawk-Eye system suggests that in both cases these calls were measured as being 1mm IN, meaning the ball was 1mm from being out.

Have a look what the manufacturers of Hawk-Eye have to say about these two controversial calls at here.

Could Hawk-Eye have been wrong in either or both of these calls and what does it mean that it is 2-3 mm accurate but can suggest that the ball was in by only 1mm?

Here are some points that may effect the accuracy of the system.

The camera capture rate of 500 frames per second may be too slow for the hard hitting tennis game of today. Andy Roddick has recorded a fastest serve at 155 mph and ground strokes are often hit with a similar speed. Assuming a capture speed of 500 frames per second or 1 frame every 0.002 seconds, the ball will have moved about 139 mm for every video frame. This may not be sufficient data to determine the position of the ball to within 1 mm.
The more cameras that are used the better the chance of tracking the ball and the higher the accuracy. However there are possibilities of occlusion by players, tennis rackets and the net, which will lead to reduced accuracy.
High speed video capture also needs excellent lighting. We have discussed the importance of lighting for high speed capture in a previous post . Therefore the system will work best under a roof with artificial bright lighting and will possibly have a problem tracking the ball outdoors, particularly when there is cloud cover or as it gets later into the evening.
Assuming everything is perfect for capture, the center of the ball has to be identified as accurately as possible too. If a camera sees the ball at a funny angle or partly occluded the center may not be correctly defined by this one camera and the position of the ball will be inaccurate.
The skid and compression of the ball is being estimated and extrapolated based on the trajectory of the ball before and after the bounce. Any inaccuracies in tracking the position and flight of the ball will become larger during an extrapolation (estimation of the movement).

The Hawk-Eye system may not be perfect but it is definitely a step up from the eyeball view of a line judge, particularly when the ball is moving at high speed. We believe Hawk-Eye has improved the line calls in Tennis and this is great for the players and spectators alike. However it still leaves room to debate exciting points and close matches. Enjoy the US Open Tennis and hopefully we will not see any controversial Hawk-Eye calls.

Which Sport Has Bigger Hits, Rugby or Football?

2009-08-31T14:21:00.000-07:00

Most of us who have watched or played both Rugby and Football know that the tackles are often hard and dangerous. We also regularly try to compare the hits. Is it worse to be hit hard in a rugby tackle or in football?

On the football field the force of the hits look more spectacular. Players can be tackled in numerous ways, even with the head. The aim of the tackle is to stop forward progression and bring the player down to stop the play. In a great tackle the player is also trying to make the receiver or ball handler fumble. In getting hit there is the added concern for the wide receivers who have to watch the ball and often jump for the catch. They can get hit while still in the air and without expecting it. Of course the athletes are also wearing padding and helmets and therefore have some form of protection.

In rugby the tackle is meant to stop forward progress of the ball handler and to simultaneously bring him to the ground so that he can not pass the rugby ball out quickly. Tackles in rugby often need to be lower (around the knees or waist) to ensure the player goes down. The tackle also does not stop play and players need to be ready to get up and tackle again almost immediately. Of course in rugby there are no helmets or pads, so there is little protections for a big hit.

OK so which tackle is harder on the player? We could measure the speed of the players as they run into each other and weight that against the benefits of the padding. In the end both sports have big hits and there are too many differences in the rules of the game and the equipment to truly compare them. So take a look at these two videos, the first of big hits in rugby and the second of some big hits in football and make up your own mind.

Hope you enjoyed watching those big hits. The Tri-Nations Rugby Tournament between South Africa, Australia and New Zealand is nearing an end as South Africa continue to dominate World Rugby. Meanwhile the NFL preseason is in full swing and starts proper in mid September. So enjoy the big hits from the upcoming Tri-Nations games and NFL season.

Let us know which sport you think has the bigger hits and why.

Video Analysis of Baseball Hitting

2009-08-26T08:29:00.000-07:00

The only way to win in Baseball is to get some hits. Looking at the statistics of Major League Baseball, where most of the best players and hitters in the world play, we can see that hitting is more difficult than it looks. Babe Ruth for example had a career hitting average of .342, while this 2009 season Albert Pujols leads the MLB on hitting average of .333.

This means that Babe Ruth only hit a base hit or home run 34.2% of the times he was up for bat, while the best hitter in the MLB this season, Pujols has only hit 33.3% of the times he has been at bat. These hitting averages for the best players seem low, but we should also consider the challenges of hitting a baseball pitch and understand that hitting averages over 30% are in truth very good.

Here are some of the challenges:

The pitcher can throw a fast ball, slider, curve ball and many other variation. The hitter needs to read the pitch correctly to get a good hit.
As a strike will only be called if the ball is pitched in the strike zone, this is the best zone to swing the bat through. However the pitcher can try to fool the batter by pitching a ball that looks like it will go through the strike zone but then fades away or drops out of the zone.
Once the batter is able to make contact with the ball, he still needs to find a gap in the outfield so that he can run to first base and score his hit. This requires timing and control to get the ball into the gap.
Of course the ultimate is to hit a home run. This requires timing and power to hit the ball far enough and high enough to clear the outfielders and the fence.

Improving hitting mechanics can help a player improve his hitting average. Here we will take a look at some video of a young hitter at practice and discuss some of the important aspects of hitting.

Our hitter here is practising by hitting balls that are tossed up to him and therefore may not be falling in the strike zone but we can still examine his hitting technique.

The video camera in this instance has been set up so that we get a side on view of the hitter, this allows us to examine his stance, hips and shoulder rotation as well as take a look at his bat swing plane. Another aspect of this video that we like is that it is high definition. Unfortunately because the capture rate was around 30 frames per second it can be difficult to see the bat swinging through to track the swing plane but we have made our best effort to track this.

Taking a look at the swing itself, we can break it down as follows.

Our hitter loads up on energy for his swing by rocking back onto his back foot. This allows him to get ready to swing his bat at the ball.
He steps forward a little with his front foot. He does this to get good position on the pitch (or in this case toss) and to open up his stance and allow his hips to rotate through.
He rotates his hips and shoulders through to make contact with the ball.

Steps 1 and 2 in this case look good. Our hitter has setup well to hit, and he has moved his front leg toward the ball to open up his stance to get a good hit.

In order to create power though, we want to remind you about the kinematic sequence. We discussed the kinematic sequence when we talked about Tiger Woods' golf swing. The kinematic sequence is the sequence of events that creates the bat speed. To create good bat speed the hitter needs to rotate his hips, shoulders, hands and bat in that order, with each following segment moving faster than the previous segment.

Here is how it works. The hitter loads up to hit as can be seen in step 1. He then steps forward to open his stance. His hips now need to rotate through toward the ball, but his shoulders should remain behind. By rotating his hips and leaving his shoulders behind he creates potential energy. The shoulders then follow the hips, as the hands and bat are now left slightly behind and with potential energy. Finally with perfect timing the hands follow and then the bat, to hit the ball in the strike zone and with power and control.

In golf, the ball is not moving and so it is easier to practice the kinematic sequence. In baseball hitting the ball can be pitched with much variation and it can be much harder to get this timing correct. However in baseball we once again have a smallish strike zone as well as a a hitting angle of only 90 degrees (between 1st and 4th base), therefore the kinematic sequence must be employed in the same way.

We took some snap shots of our hitter at key moments to examine his hip and shoulder rotation more closely.In the first image we can see our player setup correctly. His weight has been moved to the back foot and his bat is nicely positioned

His pelvis alignment can be seen with the blue line, while his shoulder alignment is represented by the red line. At this point, prior to loading and before the actual swing starts, his pelvis and shoulders are aligned.

In this second image, we can see that our player has now rotated through and is ready to make contact with the ball. In this case we can see that his hips (blue line), shoulders (red line) and bat (white dot on yellow trajectory) are all already lined up. The timing of his kinematic sequence is a little too fast, his shoulders, hands and bat have caught up with his hips too early. To create optimal power, his shoulder rotation should be following his hips, his hands should be following his shoulders and his bat following his hands. The result of this mistiming is that our hitter will strike the ball early and with less power.

Our player though does swing through a nice arc with his bat (yellow trajectory). We can see that he keeps his arms extended through the swing. This allows him to increase his bat speed and follow through with the hit.

In a final thought, our player has a good swing. He loads up nicely, steps toward the pitch and swings his bat through well. His sequence timing may be a little too quick, but this may also be because the ball is being tossed up to him rather than pitched and he has to reach for it outside the strike zone.

Baseball hitting and pitching lends itself well to video analysis, because the athlete is standing in one spot and hitting or throwing. So get your cameras out and make sure to follow the rules for setting up to capture good video for analysis and you will be able to analyze your hitting or pitching in much the same way as we have done here.

We would like to thank Mike and Aaron Kocourek for this video.

Federer Serves His Way Towards the US Open

2009-08-25T11:45:00.000-07:00

Last week, Roger Federer won the Western & Southern Financial Group Masters tournament for the third time. Only Mats Wilander, Andre Agassi, and Pete Sampras have done the same (Wilander actually won it four times). This tournament is part of a series of tournaments leading up to the US Open, and the players use it as an opportunity to reacquaint themselves to the hardcourt surface. After having been in a bit of a slump, partly due to injuries and a formidable opponent by the name of Rafael Nadal, Federer appears to have returned to winning form as of late, and is once again considered a favorite in the upcoming US Open.

Although Federer's serve is quite respectable in terms of speed (averaging around 120 mph for his first serve), it is his ability to disguise the spin and direction that make it extremely effective. As Federer has demonstrated, blistering serves can be returned consistently if the returner can anticipate where the ball will be hit. By keeping his opponents from being able to easily read his serve, adjusting the pace only increases Federer's effectiveness.

One of the main ways Federer is able to disguise his serves is with a consistent toss. As is true with most sports, keeping your eyes on the ball throughout a point/play is one of the basic concepts that helps you play well; tennis is no different, and a server can give away a lot of information about the type of serve he will hit by significantly moving his toss around. By tossing the ball in the same location, and instead adjusting his swing path to direct the ball and apply various spins, Federer gives his opponents just a fraction less time to anticipate where the ball will go; and at 120 mph, that lost time can make a big difference whether the serve is returned successfully.

Of course, just knowing your serve's effectiveness can be improved by having a consistent toss is only half the battle; having the ability to do this and make minor adjustments to your swing path/grip (not to mention having perfect timing) are just some of the skills that separate us amateurs and weekend warriors from the pros. Below is a slow-motion video of one of Federer's serves at Wimbledon. Enjoy, and learn what you can from perhaps the greatest tennis player of all time (to this date, anyway - keep practicing kids!).

Analyzing Usain Bolt's 19.19 Second 200m World Record

2009-08-21T07:16:00.000-07:00

The Scientific Research Project at the 2009 IAAF World Athletics Championships has released the data for the 200m final and now we can break down Usain Bolts incredible 200m World Record of 19.19 seconds.

Click on the table below to get a closer look.

Let's pick out the key points for this race and see if we can compare them to his 100m splits.

Bolt's reaction time in this race is 0.133 seconds. This is much better than his 0.145 second 100m world record reaction time. However we have already discussed this in a previous post and know that Bolt can start fast too.
As expected Bolt runs the second 100m (from 100-200m ) faster than the first 100m. This is expected, as the start and getting up to speed takes time, while the second 100 meters can be run at close to maximum speed. Bolt's first 100m was run in 9.92 secs with the second hundred taking only 9.27 secs (a negative split). Interestingly, Michael Johnson ran the second 100 meters of his then World Record breaking 19.32 sec 200m race in 9.20 secs, which is faster than Bolt's second 100m in this race.
Bolt's maximum velocity during the 200 meter race occurs somewhere between the 50 and 100 meter mark. His average velocity over this 50m part of the race is 11.57 m/s (25.88 mph). In comparison his 100m maximum velocity was 12.27 m/s (27.45 mph). Once again this is to be expected, as the 200m athletes needs to have reserves to complete the race and cannot run at the same speed as in the 100m race.
Bolt slows down over each of the last two 50 meter splits as he begins to fatigue, covering each of the following 50 meter splits 2 tenths of a second slower. Watching the race, we can see that he is really straining to run fast, but he is still slowing down. It is expected that any athlete will slow down over the last 100 meters as the muscles tire, two hundered meters is a long way to go at full speed. We have mentioned that in this World Championships Bolt had already run four 100m races and three 200m heats before lining up for the 200m final. This has us excited at the prospect of seeing Bolt break this 19.19 second World Record, when he is fresh and has not run seven previous races.

All that is left to say is that we can expect Bolt to go faster in the 200 meter and 100 meter races in optimal conditions.

There is one record he does not hold yet and that is of the fastest 100m relay split. This record is held by his Jamaican team mate Asafa Powell in 8.70 secs. The anchor leg relay split is much faster than any of the other sprint splits, because the athletes have a flying start and are therefore able to reach top speed much sooner in the 100 meter distance. If Bolt anchors the 4X100m relay in Berlin this week, we expect that relay split record to be broken.

Comparing Usain Bolt's 100 meter and 200 meter World Records

2009-08-20T12:34:00.000-07:00

Usain Bolt continues to amaze us with every race he runs. In destroying his own 200 meter world record from the Olympics, he has now set 5 world records in five Olympic or World Championship event finals in a row.

Watch video of the 200 meter race from the 2009 IAAF World Athletics Championships below. The final recorded time and the new record stands at 19.19 seconds, an incredible 0.11 seconds faster than his previous world record.

The 200 meter sprint record is usually a faster time than if you had to double the 100 meter record. This can be seen if we compare the more recent (since the use of electronic timers) progression of world records between the 2 events. As an example, when Donovan Baily held the world 100m record of 9.84 in 1996, the 200m record was held by Michael Johnson at 19.32 secs. This 200m time is faster than double the 100m record at the time.

In both the 100 and 200 meter races, the athletes start from the blocks and it usually takes them around 60 meters or more to reach maximum speed. In fact we saw from analysis of Usain Bolts 100m world record that he reached top speed at 65 meters in that race. Now in the 100m, the athletes maintain that speed for 40 or so more meters, while in the 200m they have 140m more to go and therefore maintain their top speed for longer. In fact the 200m race often has negative splits for the top athletes, meaning that they run the second 100 meters faster than the first 100 meters.

It is therefore interesting to note that if we double Usain Bolts 100m time (9.58) we get 19.16 secs, which in this case is faster than his new 200m world record of 19.19 secs. I am not trying to make the case that this 200 meter world record is not extraordinary, but why is this the case?
Watching the 200m race, he seems to be straining at the end, by this stage of the race his muscles must be burning, as he tries to maintain his maximum speed. He also said in an interview after the race that he felt tired and well he should after running all the 100m and 200m heats and finals. It is possible that this fatigue meant he could not run the 200m as fast as he possibly can. Seldom has the 100m and 200m world records been held by the same athlete or even broken by the same athlete at the same event and so this may be a factor in his 200m time.

Examining the splits and his maximum velocity to compare his 200m to his 100m world records, will give us more insight into what we can expect from Bolt in the future. From this past records history we can speculate that his 200m record is going to be smashed again soon and the 19.0 second barrier is not out of the question.

It is fantastic watching such an incredible athlete run and we hope to learn as much as possible about his biomechanics by watching and analyzing the video footage.

Biomechanical Analysis of Usain Bolts 9.58 sec World Record

2009-08-17T14:50:00.000-07:00

At the IAAF World Championships in Berlin, the German IAAF Member Federation, DLV, in cooperation with the IAAF is carrying out a major Biomechanics Project.

The project presented the reaction times and splits for all the finalists from the 100 metersemifinals and the final at the 2009 IAAF World Championships in Berlin.
We thought we would present them here and try to predict just how fast Usain Bolt can run.

This table gives us some real insight into Bolt's race. Lets take a look at some crucial points in the race. You can click on the table to see the details.

Of the 8 finalists Bolt has the 3rd slowest reaction time to the gun, at 0.146 seconds. Both Asafa Powell with 0.134 secs and Tyson Gay with 0.144 secs react faster.
By the 20 meter mark though Bolt has caught up all this time and gone ahead of Powell by 0.03 secs.
From the 20 meter mark on, Bolt is away and getting further away over each 20 meter interval. Although we can also see that Tyson Gay is able to hang pretty close between 20 and 80 meters.
Bolt reaches his top speed of 12.27 m/s or 27.45 miles per hour at the 65 meter mark. This can be seen in the second graph presented by the IAAF Biomechanics Research paper.
From 80 to 100 meters Bolt actually begins to slow down. We can see that his time for the last 20 meters is 0.05 seconds slower than his fastest 20 meter split of 1.61 seconds. We also know that he reached his maximum speed at 65 meters and everything after that was a little slower.
One last thing to note is that in this race there is a tail wind of 0.9 m/s. This is legal but it does give the athletes a slight advantage as it pushes them along.

To determine how fast we think he can run, lets look back at the Beijing Olympics and remember how analysis of that race suggested that if Bolt had maintained his speed through the last 20 meters and did not begin celebrations, he could possibly have run the 100 meters in 9.55 seconds.

His current world mark is pretty close to that already, so where can he improve to make up the time. So here are some key factors that are critical to determine how much faster he can go.

Firstly look at the table again and at Bolt's reaction time (RT) for his semi-final. In this race he gets out in 0.135 seconds as against the 0.146 seconds in the final. We also see that he completes the first 20 meters in the same time in both the semis and final, while he definitely seemed to be cruising in the semi-final. It has also been suggested that Bolt actually covered the first 20 meters in Beijing faster than he did in Berlin. This is up for debate though, as if you remember from our post on that study, the video analysis was done using broadcast footage where the camera setup was not optimal. In any case, Bolt can definitely get out of the blocks faster and should be able to cover that first 20 meters faster than he did in Berlin.
The prediction from the Beijing Olympics was based on the suggestion that Bolt could maintain his speed at 80 meters through to the end of the race. In Berlin however, he is not able to do this and slows down a little over the last 20 meters. We also notice that all the athletes in the final ran slower over the last 20 meters, than in the split between 60-80 meters (which was the fastest for all of them). Therefore it may be impossible for a 100 meter athlete to maintain their speed over the last 20 meters and the Beijing prediction may have been optimistic in this regard.
In the last 10 meters in Berlin, Bolt takes a look out of the corner of his eye to check on Gay. We don't believe this could have caused too much of a slow down. In fact if we look at his average velocity at the 90m and the 100m mark from the research, we can see that he does not slow down between those 2 points. But lets assume he could have been 1 or 2 hundredths of a second faster if he had not checked.
The 0.9 m/s tail wind in the final in Berlin will definitely have helped Bolt. A tail wind of up to 2.0 m/s is considered legal for a record to stand. Therefore there is an advantage to be gained with the right conditions.

Finally we have some sort of answer. We think Bolt can definitely run faster. If he improves his reaction time and runs hard through the finish in the right conditions, we have no doubt a new world record will be set.
I am sure we would all love to see an athlete challenge the 9.50 second barrier and Bolt may have it in him to do just that. We look forward to watching it all.

Can Usain Bolt Run Any Faster?

2009-08-16T18:37:00.000-07:00

In a recent post we asked the question: How fast can Usain Bolt Run? In this post we introduced you to a study that suggested he could have run the 100 meters at the 2008 Beijing Olympics in less than 9.6 seconds.

At the 2009 IAAF World Athletics Championships, today he proved just that, shattering his own World Record by running the race in 9.58 seconds. Even then he still had time to take a look out of the corner of his eye at Tyson Gay, his closest competitor, who ran an impressive 9.71 seconds

If you missed this amazing race, take a look at the video below.

Unbelievable! The only question left is how much faster can he go? Bolt himself believes that he can run the 100 in 9.4 seconds. To us this seems a bit out of reach, although we believe he will go faster than 9.58.

We would love to hear what you think.

Amazing Gymnastics Vaulting at the US Visa Championships

2009-08-14T15:59:00.000-07:00

Gymnastics really is a great sport to watch on video. There is so much that can be analyzed from a biomechanics and physics point of view too.

Sometimes though, it is just fun to watch in awe as one of these gymnasts does something amazing.

Here is David Sender doing a Yurchenko Double Pike on Vault at the US Visa Gymnastics Championships. During the move David jumps backward off the springboard onto his hands on the vaulting horse. From there he does two and a half back flips in a pike position (legs straight and hips bent), to land back on his feet.

Amazing what the human body can do and he performs it well, getting great height and control.

Video Analysis of the Back Flip

2009-08-12T12:34:00.000-07:00

When most people think of the Olympic Games, the first sport that comes to mind is Gymnastics. Supremely strong and fit athletes flying through the air, somersaulting and twisting. The sport defies gravity and leaves us all in awe.

The sport of Artistic Gymnastics is performed by moving the body, often through the air, and there are no rackets, bats or balls involved. Because of this, video analysis of different gymnastics movements can provide excellent coaching and feedback for the athlete. Gymnastics is all about the technique. By applying the correct technique and timing, the athlete will achieve the desired results. In most cases, there are no outside influences and therefore good biomechanics will result in good performance.

As a young gymnast myself, I watched and analyzed countless hours of my own technique on video. It really is very easy to set up. Most gymnastics moves take place in a small area, so you only need to ensure that the camera is set up so you can see the complete movement in the field of view and also that the camera is set up at the correct angle to analyze the movement you want to assess.

In college, I continued to analyze my own and my teammates gymnastics technique using video. One very common analysis we did was of the standing back flip. Many gymnastics elements have the back flip as a core component. A double back flip is simply 2 back flips in a row without touching the ground in between, a full in - full out is a double back flip with a twist in each of the flips. The list goes on, but what is important is that the technique used to start a back flip is the same technique that is used to begin many of these other flipping and twisting maneuvers.

Capture video to analyze your back flip requires some easy setup:

Set up your video camera, so that the gymnast is standing sideways to the camera. Most of the analysis of a back flip is done in this side on (sagittal) view, such as jump height, lean and rotation.
Remember to fill the field of view. You do not want your camera to be too far away so you have a lot of empty space around your subject. You also do not want it too close, so that the gymnast jumps out of the camera view. A little trick to know, is that most cameras have a rectangular field of view (they are wider than they are high). So flip the camera on its side to get closer to the gymnast but still be able to capture the height of his flip. If you do decide to flip your camera on its side, make sure you have some video editing software that will allow you to view the video right way up, otherwise it may be difficult to view properly.
Set your gymnast up with a plane background (such as a white wall) behind them in the image. This will allow you to mark a specific height on the wall and thereby measure their height.
If you really want to measure angles of the joints, such as the knee or hip, it is best to mark these points with a bold marker pen so that you can see them in the video.

Lets take a look at some video I found on YouTube. The video also give you some instructions on how to do a good back flip. The video camera itself is not setup in the optimal position to make good measurements of the gymnasts jump height, rotation or proper take off technique, but it is still easy to see that he has good technique.

This gymnast really does a very good standing back flip. The most important part being the take off which will allow the gymnast to perform any variation on his back flip from there.

There are 3 phases to the back flip take off:

The loading phase: In this phase the gymnast bends his knees and swings his arms backward in preparation. The idea is to create the energy needed to jump up into the air and rotate over in the flip. By swinging his arms backward and bending his knees, the gymnast is loading up with potential energy. As the video points out , you do not want to bend your knees too much or you will need to use the energy to get yourself back into a good load position for the take off.
The take off phase: Now the gymnast drives his arms upward and straightens his knees quickly as he jumps off the ground. The head is very important in this phase of the take off. If you throw your head backward , you may create a lot of rotation but you will not be able to jump as high. Therefore it is important to keep the head looking forward and still. Coaches suggest that the optimum angle of lean for the take off is between 75 and 80 degrees from the floor. The gymnast in this video looks to have this angle perfected.
The tuck: For the last part of the flip, the gymnast needs to rotate over so that he can land back on his feet. If the take off is good, then this part should be easy. By taking off leaning slightly backward (angle of 75 to 80 degrees), you have already created the rotation you require and all you need to do is bring your knees up to your chest. By bringing your knees up you will increase this rotational speed and easily complete the flip.

OK, before you try a back flip on your hardwood floors, remember that it takes practice and numerous drills before most gymnasts are doing good back flips. If you are intent on learning one, then get into a gym with mats or a foam pit and a coach. Then get out your video camera and film yourself to see what you are doing and correct your biomechanics from there.

From personal experience, I will say it is well worth the effort to learn how to do a good back flip.

If you are a gymnastics fan, look out for video from the 2009 US Gymnastics Championships starting today in Dallas, Texas. You can watch a live webcast at http://www.usa-gymnastics.org/events/2009/visachamps/webcast.php .

Video Analysis of Sprinting: From the Start

2009-08-06T10:50:00.000-07:00

In the 100m and 200m track sprinting events, the start can win or lose a race. In the 100m the winning difference is often measured in 100ths of a second, therefore any advantage that can be gained at the start could be crucial.

At the IAAF World Championships next week, Tyson Gay will take on Usain Bolt for the title of worlds fastest man. So far in 2009 both athletes have put up some impressive times and the first meeting between them this year should be fast, close and exciting. Usain Bolt is the Olympic champion and world record holder. We have previously discussed how fast he could possibly run. Tyson Gay is the reigning World Champion and recently ran the 100m in 9.75 seconds at the US Championships.

With both athletes being at the top of their game, victory may be decided by their start. Neither of them is known for their explosive or fast starts. Bolt has an incredibly long stride length and eats up ground with each step while Gay has unmatched leg speed. The start though is crucial and we have therefore decided to look at some video and examine the start.

Below is some front on video of Tyson Gay at the US Championships. We want to focus on his start.

A good start requires that the athlete sets up correctly. Here are some key factors for the set position before the start gun sounds.

The hands are set up on the line and the shoulders and upper body should lean forward over the hands. Track coaches suggest an angle of about 15 degrees (The angle between the shoulders and hands and the vertical). Although we cannot see the angle at which Gay is leaning (this would need a side on view of his start), we can see that he is leaning forward and ready to explode from the blocks.
The angle of the knees in the start position must allow the athlete to push away from the blocks with as much power as possible while at the same time being able to get their feet through to begin running. The optimal bend of the front knee should be around 90 degrees to provide the biggest lever to produce push off. The back leg needs to be bent less than this at about 60 degree so that it is able to still push off hard but will straighten before the front leg and have time to come through for the first step.
Both legs need to push off almost simultaneously at the start of the race. The athlete cannot be sitting back on either his front or back leg at the start.

Tyson Gay sets up well and in this video he explodes from the blocks, pushing off with both legs quickly. Both legs straighten completely, with the rear leg leaving the blocks and starting to drive through before his front leg (left leg) is completely straight.

Gay also uses his arms to explode out of the blocks, as well as maintain good balance. Watch as his right arm drives backward and his left forward. This motion provides extra forward momentum, but it also ensures that as he starts he does not fall over to one side. The arms act as a counter balance to the motion of the legs. In this start his right leg will take the first step on the track and therefore his left arm needs to be forward to balance this motion.

Moving forward to that first right foot step on the track, we can see that Gay's head and chest are still down low. His arms are driving hard and fast. If you pause the video you will see them as a blur. We can also see that his first step is not too long. In fact his head, chest and hips all remain in front of his foot for this first step. This allows him to continue to stay low with his body. If he took a longer first step, it would force his chest up, which would in turn slow down his speed. His chest and head stay down for as many as 16 steps allowing him to lean forward during this start and continue to accelerate.

His start technique looks great here and although we do not know what his reaction time to the gun was, we can see that he was able to accelerate well from the start and this is why he put up such a fast time.

As I looked through more videos on Tyson Gay's start, I came across one from tttjump that suggested that Gay's knee rolls forward at the start. If you study the slow motion of the start in the video above you will see what this means. Gay's front leg (his left) moves forward and down, in fact bends a little more, just after the start and as his hands leave the ground.

The suggestion is that this extra bend of the front knee at the gun, causes a delay in his ability to get off the blocks. On closer examination we can see that his back foot is driving already (straightening) as his front knee "rolls" forward. This may be causing him to push off with less power from his back leg as he may need to slow it down, to give the right leg time to get into a position to start its push off.

From a biomechanical standpoint, this would suggest that Gay's front leg is not bent to the most optimal position to explode out of the blocks. He may be bending it a little more after the start to get more push off power. The split second it takes to bend the knee that little bit more and the small amount of back foot push off power that he may lose, could determine the outcome of the race against a phenom like Usain Bolt.

Once again from the standpoint of biomechanics, this problem could possibly be solved by simply adjusting Tyson Gays starting blocks or position slightly, allowing his front knee to set up in a more optimal position for his starting style.

Of course for this World Championships, it is too late to make any changes and Tyson Gay should provide Usain Bolt some really stiff competition when they hopefully meet in the final in Berlin.

If you will be watching or filming some video of any of the action at the IAAF world championships and would like to share some video for analysis, please let us know.

How Polyurethane Swimsuits Affect Swimming Mechanics

2009-07-30T09:11:00.001-07:00

The World Swimming Organization FINA has recently made rules which will ban the new polyurethane swimsuits in spring next year. The FINA World Championships are taking place this month in Rome. Records are being broken, wins are being challenged and the polyurethane suit as at the center of all this controversy.

At the 2008 Olympic Games, Speedo introduced the LZR Racer swim suit that included some polyurethane panels over areas of the body at which the highest drag is experienced. The idea was to squeeze any loose body tissue (muscle or fat) that could cause water resistance. This would reduce drag and therefore increase the swimmers' speed in the water. Recently swimsuit manufacturers decided that instead of just making panels of polyurethane they would create the complete suit from polyurethane.

A full body polyurethane suit allows an air pocket to be created between the water and the skin. The resistance of air is much lower than that of water and therefore the drag in the water is reduced. The suit also aids in increasing buoyancy. Buoyancy is a measure of how well the swimmer floats in the water. A swimmer (without a polyurethane suit) will generally use more of his kicking power to stay on top of the water. The advantage of the higher buoyancy is that he can now use that kicking power to propel himself forward.

This decrease in drag and increase in buoyancy brings up two important questions: does the polyurethane suit change the biomechanics of the swimmer and will the swimmers need to change their kicking motion or even their stroke, when they are forced to abandon their speed suits next spring? Video analysis can definitely play a part in identifying how the biomechanics may change.

At the FINA World Championships, Michael Phelps finished second to Paul Biedermann of Germany. Phelps was swimming in his Speedo LZR swimsuit with polyurethane panels, while Biedermann was wearing a full body polyurethane suit. Biedermann also smashed Phelps' world record in the same race. Did the full polyurethane suit provide an advantage?
Take a look at the video here:

Unfortunately this is TV broadcast video and often the angles are not great for analyzing video. However as you watch, notice how Biedermann remains high up in the water particularly at the end of the race compared to Phelps. In the final 25 meters of the race we can see how Biedermann's legs remain above the water and kicking hard. His kick at the top of the water is propelling him forward quickly. Phelps' legs are deeper in the water and he therefore is using much of his kicking power to stay above the water rather than to propel him forward.

Before we jump to any conclusions that the polyurethane suit gave Biedermann the advantage, we need to remember that there are numerous other factors. Fatigue would definitely be a factor. If Phelps was fatigued at the end of the race and Biedermann was still strong, this would explain how Biedermann continued kicking at the top of the water. Of course the buoyancy of the polyurethane suit may have allowed him to conserve energy throughout the race. We also do not know what normal kicking (without a suit) is like for both swimmers.

To truly understand whether the ban on the polyurethane suit will make a difference to the swimmers' biomechanics we will need to analyze the swimmers independently, comparing their swimming motion in the suit and how they swim without the suit.

We will continue to watch the FINA World Swimming Championships with interest and will also look forward to seeing how the ban on the polyurethane suit will affect the swimmers technique in the future.

We look forward to your comments and please Retweet, Digg or post our blog to Facebook and share them with your friends.

"Heading" into the FIFA World Cup!

2009-07-28T09:08:00.000-07:00

Although most of us try to avoid striking our heads on objects whenever possible, football (soccer) players often use the tops of their heads as an effective means to control the ball. Sometimes they have the luxury of letting the ball come down towards them, and they can simply direct the ball to a teammate. However, there will be times an opponent is in the vicinity (e.g., defenders around the goal defending a corner kick), and the player will need to have terrific position, timing, and strength to win the battle for a solid strike on the ball with their head.

We found a wonderful video demonstrating a header. This video makes use of many of the principles we discussed in setting up a good video capture (http://videosportsanalysis.blogspot.com/2009/03/video-analysis-of-sports-101.html), including a well-positioned (and stationary) camera, a solid-colored background, and a sufficient light source placed behind the camera . Unfortunately, the video cannot be embedded into our blog, but can be viewed here: http://www.youtube.com/watch?v=5VroNiXG8X4

In the above video, we see the player prepare to jump by swinging his arms backwards while bending his knees. As he goes into the jump, his arms come forward and upward, and he extends his hips, knees, and ankles. Getting into proper position and executing a well-balanced jump will improve the player's chances of striking the ball before his opponent can get to it. And to increase the force with which he strikes the ball (in this case, he is hitting the ball in a forward direction), he flexes his neck and anterior core muscles (e.g., his abs), and brings his arms back down just before impact. The player's strength comes into play during every aspect of this shot, including the preparation, the jump, and the strike.

Below, we've included a few highlights of some exciting headers during matchplay. Enjoy the clips, and we hope you are making good use of your cameras to film some excellent video for analysis!