Thursday, September 23, 2010

Dane vs. Jordy: Who Does Higher Surfing Aerials?

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.

Wednesday, September 8, 2010

Why is Nadal Serving Faster at the US Open 2010?

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.

Tuesday, August 31, 2010

Comparing Federer's Between the Legs Shot

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.

Monday, August 23, 2010

Measuring Michael Jordan's 1987 Slam Dunk Contest Vertical Leap

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, 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. 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:
  1. Height of the rim is 120 inches above the ground.
  2. Michael Jordan is listed at 6 foot 6 inches or 78 inches.
  3. 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?

Monday, August 16, 2010

Measuring Vertical Leap at a NBA Slam Dunk Contest

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.
  1. 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.
  2. 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.
  3. 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.
  4. 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.
  1. Width of the backboard is 72 inches
  2. Height of the bottom of the backboard is 114 inches above the ground
  3. Vince Carter is listed at 6 foot 6 inches or 78 inches
  4. 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:
  1. 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.
  2. 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.
  3. 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.
  4. 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.  

Wednesday, July 28, 2010

Does Kicking Help to Paddle Faster in Surfing?

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.

Thursday, July 22, 2010

The Rules of Sprinting in the Tour de France

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.

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