How Fast can Usain Bolt Run?

The IAAF World Championships begins in less than a month and all eyes will be on the 100m and 200m world record holder, Usain Bolt from Jamaica. We all remember the Beijing Olympics in 2008, when Bolt ran the 100m in 9.69 seconds, throwing out his arms and pumping his chest before crossing the line. There has been a lot of speculation about how fast he could have run with some suggesting a time of 9.55 seconds http://sports.espn.go.com/oly/trackandfield/news/story?id=3583692 .

The publishers of the study above, made use of video analysis to estimate this potential world record time. In fact they used video from Beijing Olympics broadcast productions from NBC, BBC and NRK (a Norwegian Channel). If you are a regular reader of our posts you will already know about many of the techniques they used to analyze the video. Lets look at how they did it.

When you or I setup to capture video of a sporting performance, we know how important the position of the camera is. In this case however the researchers did not have access to the stadium and athletes in Beijing and therefore had to make use of broadcast footage. In most cases this footage includes moving cameras and camera angles that are not always conducive to accurate measurement.

The publishers of the article used basic physics to estimate the possible finish time for Usain Bolt had he not celebrated 20 meters before crossing the line. The basic equations are well known:
Velocity (speed) = Distance/Time
Acceleration = Velocity/Time

So if we can find the distance Bolt covered and the time he took to cover that distance we would have his velocity or speed. We could measure that speed, from the video footage, over numerous intervals to determine how it is changing. Likewise, if we know his velocity (speed) we can measure his acceleration and how it changes over the same intervals.
The publishers of the study estimated Bolts speed and acceleration at the interval before he started to celebrate. At this point his speed and acceleration slow. To determine the predicted finishing time, the researchers assumed that Bolts acceleration could be maintained over the last 20 meters of the race, had he not celebrated. In this way they were able to predict a finishing time of 9.55 seconds.

You probably want to know how they were able to determine distance covered and the time it took. This information was all obtained from the broadcast video. The video used was from NBC and can be found at http://www.nbcolympics.com/video/share.html?videoid=0824_HD_ATB_AU_CE552 . Below is similar video of the race :


In the video you will see the camera rail running from the left to the right at the bottom of the image. This camera rail has bolts spaced evenly along it. By knowing the distance between the bolts on the track and that the start line is at 0 meters and the finish line at 100 meters, we can determine Usain Bolts position relative to the rail bolts at numerous intervals.

You will also see the stadium time clock and the broadcast time clock in the video. These clocks can be used to determine the time at which Bolt reached each interval.
We now have all the information we need. Distance covered and the time it took. From this we can determine his speed and acceleration at all intervals and predict his finishing time had he not begun his celebrations early.

We would like to thank the study authors H. K. Eriksen, J. R. Kristiansen, Ø. Langangen and I. K. Wehus for doing this fun study and we look forward to seeing whether Usain Bolt can get anywhere close to this predicted World record at the IAAF World Championships in Berlin in August.

Please let us know if you want more details on this study or just want to leave a comment. We love to hear from you.

Performance Analysis of Surfing: Rodeo Clown Flip

Anyone who has seen a surfer or skateboarder pull off a flying aerial move is amazed that a human can do such an incredible trick. Although we are all completely dumbstruck by the performance of these maneuvers, these sports often have an unfair reputation of not being truly professional. We often consider these athletes to simply be kids who have spent too much time playing around on the beach.

Surfing and Skateboarding are no longer sports dominated by athletes with talent only. These professional athletes spend many hours training. Professional surfers now spend almost as much time out of the surf, working out (often with trainers) on balance balls, with weights, and in the gym and swimming pool. They do thorough warm up sessions before going out to compete and often also have cool down routines for after a surf.

The use of scientific analysis in surfing has been long in coming. There are a number of reasons for this and I won't give you a history of soul surfing, but the main reason is the difficulty of doing any physiological or biomechanics testing on a surfer. Because surfers do their sport in water and shifting, changing waves (size, direction, steepness...), it is very difficult to test them in the same conditions and obtain relevant scientific results.

Recently, for the first time a team of scientists joined some professional surfers in the Mentawais and recorded their paddle speed, surfing speed and heart-rate during surfing sessions. They also took blood samples to monitor lactic acid build-up and hydration data. These scientists were able to provide the surfers with some physiological and performance data which will surely help them to train better for competition.

Using video to analyze surfing is another way in which these athletes and other non-professional surfers could improve their performance. The professional surfers get lots of video of their performances from all different angles and we hope they use this information to make improvements. Of course, because of the changing waves and the 3 dimensional nature of surfing (moving up and down, forward and sideways), it is difficult to make comparisons with video.

As we looked through some of the video from the surfing trip to the Mentawais, we found one of Jordy Smith of South Africa, performing a Rodeo Clown Flip. We won't try to describe the move here. At about the same time at a competition in the Maldives, an American surfer, Patrick Gudauskus was completeing the first ever rodeo clown in competition. We have decided to look at both these videos and compare their performances. Jordy's wave is the first video and then Pat's wave is the first part of the second video.





Once you get over being completely amazed that surfers can do such things on a wave, take a closer look.

The first thing you will notice is that Jordy is on a much bigger wave than Pat and this can make comparison difficult. We can still look at the technique though and we will do this in stages.

1. The Setup: Jordy launches into his rodeo clown with his board facing almost vertically up at the sky, while Pat's board is about 30 degrees from the vertical when he launches. This may be because of the size of the wave. However, what is obvious is how this affects the height of the flip. Jordy's vertical entry helps project him higher into the air.
2. The Take Off: Here both Jordy and Pat transfer their weight onto their back foot. This helps them launch the board out of the water, bring the board up to their hands for the grab and creates the rotation by pushing on the back of the board.
3. The Grab and Spin: Once again they both use a similar technique here. They both grab the board quickly once they are in the air and begin their rotation. Some of their rotation has come from the back foot pushing on the board but once they are in the air they both use their heads to complete the spin. Watch how they both turn their heads to their left (the direction of spin) . If they did not use their heads to turn they would not be able to complete the spin.
4. The Top of the Flip: As they spin around both surfers actually travel upward to their high point. The high point of the flip is determined by the surfers maximum height above the wave. It is obvious here that Jordy is much higher than Pat throughout the flip. At the top, Jordy's body and board are well above the wave (we can see sky and clouds between him and the wave). Pat's board and body are at just about the height of the wave. Although in this case it does look like Jordy is much higher we need to clarify this by pointing out that Jordy is on a bigger wave (this is not controlled by the surfer) and the camera angle filming these two flips is not the same and therefore the camera angle used to film Jordy's flip may be making it look much higher than it was.
5. The Landing: The landing of course is dependent on all the other factors that occurred before, including the take off, spin and height. Jordy has rotated further and is still above the wave as he prepares to land. He therefore needs to stretch out his legs to find his landing and ride out of it. Pat, on the other hand has not been able to rotate as far, because he did not get the same height above the wave. He is forced to land low down, but by landing with knees bent and hands still on the board he too is able to ride out.
   

So both of these flips were spectacular and although they looked different they were actually performed with similar techniques and there is a lot to learn by analyzing the videos.

Unfortunately, those of us who surf for fun and do not have sponsors, do not have too many opportunities to see ourselves in action. You can however set up a camera on a beach or get someone to film you from the beach. Try to get video looking straight out at the wave from the beach. It is difficult to analyze your performance when studying video that was filmed at an angle to the wave. It is also useful to have some sort of calibration scale that can be used to measure height (as we did in a previous post on Measuring Jump Height). Of course if you can get more than one camera setup you can really take a look at your technique from multiple views, which makes sense for a sport such as surfing.

We love to hear your comments or suggestions. Let us know what you think or what you want to see posted.

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.