More than a decade ago, Peter Weyand, a science professor at Southern Methodist University, conducted a study on speed. Comparing athletes to non-athletes, Weyand clocked both test groups as they ran at their top speed. What he found shocked him.
“The amount of time to pick up a leg and put it down is very similar,” he says. “It surprised us when we first figured it out.”
So if leg turnover is the same, how does one person run faster than another?
Weyand discovered that speed is dependent upon two variables: The force with which one presses against the ground and how long one applies that force.
Yes, the air time is the same when comparing a fast group and a slower group of sprinters (although they are huge individual variations). But it doesn’t mean that their legs are moving at the same speed through the air! In fact, faster sprinters tend to accelerate their legs at a higher rate and hit the ground at a faster speed than slower sprinters.
Comparing Bolt’s mechanics at 65% and 100% of max speed, I have found that the leg was x2 faster just before hitting the ground, and even more significant was that he was accelerating his leg towards the ground x3 more at 100% max speed. Basic maths will tell us that: if force = mass * acceleration, the mass of the leg remaining the same, the force will be x3 bigger.