Analyzing Dane Reynolds in Slow Motion

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.

Analyzing Usain Bolt's 19.19 Second 200m World Record

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.

1. 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.
2. 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.
3. 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.
4. 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.

Biomechanical Analysis of Usain Bolts 9.58 sec World Record

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.

1. 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.
2. By the 20 meter mark though Bolt has caught up all this time and gone ahead of Powell by 0.03 secs.
3. 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.
4. 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.
5. 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.
6. 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.

1. 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.
2. 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.
3. 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.
4. 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.

Video Analysis of the Back Flip

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:

1. 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.
2. 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.
3. 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.
4. 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:

1. 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.
2. 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.
3. 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

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.

1. 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.
2. 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.
3. 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

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!

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!

Improving your Basketball Free Throw with Video

The NBA playoffs are now in full swing. King Lebron James is showing us all why he deserves the MVP and why the Cleveland Cavaliers must be considered the favorites for the title. Free throw shooting in the playoffs is even more critical than during the regular season and therefore we bring you a second installment of our video analysis of the basketball free throw.

In March we introduced the Video Analysis of the Basketball Freethrow and compared two different subjects and their respective shooting techniques. We focused on the angle of release in particular. This week, we captured video of our Subject 1 from March, to see if he was able to use the video analysis to make improvements. Once again we will use video analysis software to determine and quantify whether any significant improvements have been made with his technique.

As you may recall from our first analysis, it was noted that this subject could improve his chances of making a successful free throw by increasing the angle of release of the ball, so it falls on more of a downward arc as it gets closer to the hoop. Let's take a look at some stillshots that were created with some analysis software.





This week we filmed our video at a different court and set up our camera on the right side of the subject so we could see his right arm more clearly. Unfortunately in the earlier video (top photo), we needed to set up on the left side of the subject for lighting reasons. In order to compare the subjects free throw technique, we used our analysis software to create a mirror image of the subject from the March video (top photo). This allows us to watch the video and study the still shots with more clarity. When we mirror the image, it looks as if the subject in the mirror image is left handed, but of course this is not the case. The mirror image function of video analysis software is very useful for comparing left and right handed players or comparing video of movement in different directions, as we do here.

Ok, let's get onto the analysis. For the "before" shot (subject with blue shirt, top photo), we see the angle of release is 48 degrees from horizontal. For the "after" shot (subject with red shirt, bottom photo), the angle of release is 61 degrees from horizontal. This is approximately a 27% increase in the angle of release from the first to second shot. As we mentioned in the March post the higher the angle the higher the arc of the free throw. Therefore, we can safely say the ball will be coming down in more of a downward arc as it approaches the rim. If the subject continues to shoot with the technique seen in the more recent shot; this will likely result in more free throws made.

The video below shows a side by side view of the subject's free throw attempts in full motion.




Besides the improvement in release angle we can also note how the subject follows through on each shot. Although it would be easier to see from a behind or front-on view, we can still see that the "before" subject follows through across his body, whereas the "after" subject follows through more towards the hoop. Following through towards the hoop is going to help the subject's chances of shooting the ball towards the middle of the hoop, rather than to one side or another. For obvious reasons a ball moving straight toward the hoop is more likely to go in to the basket.

Following through towards the hoop on a free throw (or jump shot) helps ensure the player moves the ball towards the target throughout the shot, rather than having to rely on perfect timing to get the ball going towards the hoop. Minimizing this error of the shot going left or right makes it easier for the subject to now focus most of his attention on the angle of release relative to horizontal.

Remember to use your video camera, so that you can see and analyze your own free throws. Once you see your shot you will have a better understanding of how to improve it. We hope this posting helps you get the most out of your free throw practice sessions. Whether you need to make free throws to get into a pickup game at a park, or your team's relying on you to hit the game winning foul shot, the ability to make free throws consistently is an important skill for every basketball player to have.

Video Analysis of the Basketball Free Throw

We know why you visit our blog, to learn how to capture and analyze sports performance. Today we present our first videos and some biomechanical analysis done with free video analysis software.

Before we begin, we want to remind you that our intention is to show you the tools you can use for the video analysis of sports. We are biomedical engineers who have done research and work in sports performance analysis, but no one can be an expert on all sports. Therefore, although our biomechanical analysis is correct, our coaching tips (which we will minimize) should be evaluated with a professional coach in the appropriate sport, and must be evaluated on an athlete-by-athlete basis.

With the NCAA basketball tournaments about to begin and the regular season of the NBA about to end, we know many of you are spending a lot of time either watching or playing basketball. In honor of March Madness, our videos this week are of a basketball free throw. We have video of two subjects with very different techniques shooting a free throw. We have set up our camera on the side of the subject, as we wanted to evaluate the subjects ball release angle.
The two videos can be seen below. Notice that both the free throw shooters are right-handed therefore it would have been more appropriate for us to shoot the video from the other side of the court, so that we would have a clear view of the right arm. However, in this case, lighting conditions and other background interference meant that shooting from the left side of the athlete would result in a sharper image to analyse. We were, however, lucky that in both videos we can see enough of the shooting arm and ball to evaluate the release angle that we are interested in.





With these two independent videos there is already so much we can analyze. We can see that Subject 1 jumps quite high off the ground for his free throw and also falls forward, while Subject 2 goes up on his toes. As the camera was set up in almost the same position, we can immediately notice that Subject 2 is quite a bit taller than Subject 1 and we can take that into account in our assessment. Subject 1 is jumping in order to gain more height on his free throw. This is causing the ball to come out of his hand at a flatter angle.

A feature of many free video analysis software is that we can compare two subjects side by side. When comparing 2 subjects, it is important to also synchronize the video to a specific event. In our comparison video below, we have synchronized the two subjects' free throws at the point of ball release. We need to synchronize video for comparison because not all videos are the same length, as some subjects may take longer to shoot their free throw than others. If we tried to analyze two videos of free throws that were not synchronized, we would have a very difficult time ensuring that we could see both subjects releasing the ball at the same time. The free video analysis software we used allows us to synchronize side by side video, but not to save it out as an avi. We therefore used a well-known video analysis software to create the synchronized view you see below:



If you are a basketball coach, you can probably see a few things that can be improved for both

Subject 1 and Subject 2. Please send us your comments or coaching tips if you have suggestions.
We however are going to suggest some improvements for subject 1 based on a little bit more video analysis we did with a free video analysis software package.





Here are two freeze frame images of Subject 1 (top) and Subject 2. Using free video analysis software, we have calculated the angle of release for both subjects, and zoomed in on their arms and the ball at this release point. Subject 1 released the ball at 48 degrees to horizontal while Subject 2 released the ball at 79 degrees to the horizontal.

Now for some basic physics. The diameter of the basketball rim should be exactly twice the diameter of the basketball. In other words, two basketballs can fit through the hoop at the same time (if everything is perfect and there is no net). During a free throw or any basketball shot from the outer court, we are throwing the ball on an arc. The ball needs to move forward as well as up (for most of us) to get it into the net. The ball can either move on a flatter arc (Subject 1) or on a steeper arc (Subject 2). On a flatter arc the ball will not go as high but will move forward further and quicker; on a steeper arc, the ball will go higher and not as far. This means a free throw on a steeper arc will come down straighter and take advantage of the size of the basketball rim, while a flatter free throw will need to be far more accurate as a ball moving forward is more likely to hit the rim.

Subject 1 should try to put his free throw on a higher arc to take advantage of the physics described above. He can see immediately from this video analysis that his free throw is at a 30 degree flatter angle at release than Subject 2 and while practicing his free throws, should concentrate on releasing the ball on a higher angle. Once Subject 1 has some time to practice, we will get another video of him and see how he has improved.

Hope you enjoyed this first full Video Analysis. Remember that you too can do this type of in-depth analysis. All you need is a video camera and a little understanding. Follow us to get more tips, tricks, and understanding in using your video camera to analyze different sports.

We are happy to answer any questions or hear from you, please leave us a comment.

Video Analysis of Sports 101

Welcome to the Video Analysis of Sports blog. As this is our first article, we will take this opportunity to introduce ourselves.

We (Dennis and Dudley) have a combined 20 years experience in motion capture and biomechanics with a special interest in sports performance and injury prevention. Through our consulting company Sadaka, LLC http://www.sadakallc.com ,we offer services to sports professionals, sports equipment manufacturers, hospitals and motion analysis software and hardware companies. Some of our past clients include Titleist, FootJoy, Warrior Hockey, National Pitching Association, NASA, Shriners Childrens Hospital and Vicon Motion Systems.

Video analysis of sports performance is often the domain of professional athletes and large companies or research institutions. This analysis is done with expensive 3D video camera equipment and complicated software to ensure high speeds and accuracy. However there are some basic techniques that can be used by any individual to evaluate their own performance and get great results using a simple digital video camera and a little understanding of biomechanics. The video camera will require a small cost (we will discuss what makes a good camera in a future posting), but we will supply you with much of the biomechanics understanding for free on this blog.

Reviewing video clips can be a great way to provide coaching feedback to players, as well as a means to emulate one's favorite athletes. Whether you're a professional all-star, high school athlete, or weekend warrior, seeing yourself from a different perspective can help improve your performance and/or minimize your chances of injury.

So in this first posting, we'll start right at the beginning and describe what features make a sports clip suitable for video analysis of an individual, and what you can do to ensure the clips you film will meet those requirements. Future postings will demonstrate the various levels of analysis that can be performed on suitable videos, using a range of available software, from basic free software to detailed 3D analysis.

What makes a good sports clip?
A good sports clip of an individual shows the athlete's full range of motion (ROM) during an action, with the camera positioned such that angles can be accurately calculated (this will be discussed in more detail later). Filming the athlete's ROM can be accomplished by simply zooming out or moving the camera backwards until all the desired features are in the viewer. In general, it's recommended to have the camera as close to the athlete as possible and still capture the entire ROM, as this will make the most use of the camera sensor's resolution. For example, if we were to capture a basketball player dunking the ball we would want to ensure that our camera can see the complete action from take off until the player puts the ball in the net. Our camera would therefore need to see the ground at the take off point as well as some space above the rim of the the net.

Another important factor in obtaining a great sports clip is to make sure that your camera is stationary. There are some motion capture software available that can handle a moving camera, but for now we suggest that the camera is mounted on a tripod and is not moved while the video clip is being filmed. This means that you should ensure the full ROM (described above) can be captured in this one shot.

How you can film useful footage:
Camera placement
In general, most sports clips we watch on tv are best suited for analyzing strategy and teamwork because they provide an overall picture of many or all of the competitors and the playing field. However, when it comes to analyzing an individual's performance or technique, it's not only important to focus the camera on the single athlete, but the angle we film from must also be taken into account. It's best to use "orthogonal angles", meaning the camera is directly in front of, behind, or to the side of the athlete. Golf coverage usually does a nice job of this, providing shots of the golfer either "face-on" or "down-the-line". Here's a great face-on view of Tiger Woods' swing:



And here is a down-the-line shot of his swing:



Notice these cameras are level with the golfer; they're not filmed at an upward or downward angle, meaning it's possible to accurately calculate some angles, if that's what is desired from the analysis.

Background/contrast
Although the above clip is a beautiful view of Tiger's swing, the footage could have been improved by having him wear clothes that were a different color from the background. Black clothing with a black background can make it difficult to accurately evaluate the amount of hip and shoulder rotation - two commonly analyzed characteristics of a golf swing. Not that having a solid black background is a bad thing though; on the contrary, if you can manage to film your athlete with a solid-colored background, you are well on your way to filming some nice footage for analysis.

Lighting
As is true with taking most photos, it's ideal to position the camera and athlete such that the light source (e.g., the sun) is behind the camera and illuminates the athlete. This will provide a crisp view of the athlete, and will allow you to use a more open setting on the camera's aperture.

Now that you're up to speed on the basics of filming great video for analysis, grab your video camera and start practicing! Follow our regular blog postings, and see how you can create your own analyses of your videos, using a variety of software packages.

-Dennis Ho