Kinesiology and the 2016 Olympics Part V: Appreciating Usain Bolt

Usain Bolt made history on Sunday night, becoming the first athlete to win the men's 100 m race at three different Olympics (2008, 2012, 2016).  There have been very few to win the 100 m race at back to back Olympics, so for Bolt to do it at back to back to back is very impressive.  He is definitely the best sprinter of all time and this accomplishment may never be matched.

From a biomechanics perspective, there are several factors that enable Bolt to run at such a high velocity.  At six feet, five inches tall, he has very long legs, which enables him to cover more ground with each step and stride than his competitors.  However, being tall and having long legs does not automatically mean you will be a fast runner. Take Shaquille O'Neal for example.  What Bolt is able to do that most people with long legs cannot do is to have a very high step and stride frequency, meaning he can apply a force very quickly to the ground, pick his foot off the ground, and swing his leg through and get it back on the ground in a very short amount of time. We can measure how hard it is to rotate something by an object's moment of inertia, which is the product of the mass of the object and how the mass is distributed about the axis of rotation (radius of gyration, which is a squared value).  For Bolt, he has very muscular and long legs, which increases their mass. The length of his legs also moves the mass further away from the axis of rotation (the hip).  So, Bolt has a greater moment of inertia when swinging his legs while running than his opponents.  Imagine swinging a baseball or softball bat.  As the bat gets more massive (heavier) and longer, it becomes more difficult to swing the bat. The fact the Bolt can overcome this larger moment of inertia and still achieve a very high step and stride frequency really sets him apart from all the other sprinters.

Bolt is also a very powerful runner.  He is able to apply a larger amount of force to the ground in a shorter amount of time than his opponents, thus giving him a greater amount of impulse and a greater change in momentum.  This interactive piece from the New York Times offers a really good analysis of Sunday's race.   Although Bolt has a poor reaction time (0.155 s on Sunday, which was the second worst in the field), he is able to make up for that with his stride length, stride frequency, and his superior ability to apply more force to the ground in less time than his opponents.

Here is another piece from the New York Times that shows how Bolt stacks up against all previous medalists in the 100 m race.  It's a very interesting look at the history of the race.  Bolt still has the 200 m race to run, it will be very interesting to see if he can also win that one again.