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.

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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.