Biomechanics and the Olympics: Part VI

Sometime yesterday afternoon (although NBC didn't show the race until later last night), Usain Bolt cemented his place as the world's fastest man by again winning the 100 meter race, with a time of 9.63 seconds.  As you can see in the picture above, Bolt is clearly a few meters ahead of his closest competitors.  What makes Bolt so fast?  Well, there are a number of factors, but today I am going to talk about his stride length, step length, and stride frequency.

Stride length is the amount of distance covered from the touchdown of one foot (let's see left foot strike) until the left foot touches the ground again.  Step length is the distance covered from the touchdown of one foot (left foot) until the touchdown of the other foot (right foot).  Bolt clearly has an advantage here because he is taller than the other sprinters.  I went back and watched the race in slow motion and it took Bolt 41 steps, or 20.5 strides, to run 100 meters.  The third place finisher, American Justin Gatlin, took 44 steps or 22 strides to complete the 100 meters.  Simply put, Bolt covers a much greater distance with each step and stride than any other competitor, giving him a distinct advantage.  On average, Bolt covers 2.44 meters with each step, which is roughly equal to 8 feet, and 4.88 meters per stride, or nearly 16 feet.  Justin Gatlin covers 2.27 meters per step, which is equal to 7.45 feet per step.  These numbers are just the average stride and step lengths over the entire race.  Since each runners takes a shorter stride at the start of the race, the actual stride and step lengths are going to be greater towards the middle and end of the race.

Another critical factor in determining running velocity or speed is stride frequency, which can also be broken down into step frequency.  Stride frequency is the number of strides taken during a given time frame, typically strides per second.  In this race, Bolt took 20.5 strides over 9.63 seconds.  This averages to 2.13 strides per second, or 4.26 steps per second.  For Justin Gatlin, he took 22 strides over 9.79 seconds, which averages to 2.25 strides per second, or 4.5 steps per second.  This means that Gatlin is able to swing his legs through the running gait cycle (put his foot on the ground, and swing it back and then forward to the ground again) at a faster rate than Bolt.  But, because Bolt is able to take such a longer stride and step than any of the other sprinters, he still finishes the race faster than them.  Based on Bolt's stride length and stride frequency, and Gatlin's stride length, Gatlin would have to increase his stride frequency to 2.28 strides (4.56 steps) per second to equal Bolt's time of 9.63 seconds.  Simply put, Bolt is very difficult to beat when he is dedicated to his training and focused on the race.