Friday, February 15, 2013

The Pistorius scam

By Donald Sensing

Does Oscar Pistorius have an unfair advantage?

Published long before the present scandal of Oscar Pistorius being accused of murdering his super-model girlfriend, the article examines whether the runner's artificial "Cheetah" blade-style legs gave him and unfair advantage over able-bodied runners.

The answer seems to be yes:

A primary difference between the best sprinters and their slower competitors lies in how much force each one applies in that fraction of a second when their foot is on the ground. (A normal person running at top speed applies an average force of about twice his body weight over the contact time; Gay applies closer to 2.5 times his body weight.) The rate at which a sprinter swings his legs through the air might also seem important in differentiating him from his rivals, but all able-bodied sprinters swing their legs at nearly the same rate: about a third of a second between strides. 
"All the fast guys do it the same way," Weyand says. "If you know their top speed and their leg length, without knowing anything else you can predict the time they'll spend on the ground and the time in the air and the ground forces." 
In 2000, Weyand and a team of researchers at Harvard published a study showing that humans, from couch potatoes to pro sprinters, have essentially the same leg-swing times when they achieve their maximum speed. Says Weyand, "The line we use around the lab is, From Usain Bolt to Grandma, they reposition their limbs in virtually the same amount of time." 
But Pistorius's leg-swing times, when measured on a high-speed treadmill, were off the human charts. At top speed, he swings his legs between strides in 0.284 of a second, which is 20 percent faster than intact-limbed sprinters with the same top speed. "His limbs are 20 percent lighter," Weyand says, "and he swings them 20 percent faster."

Another clue: Pistorius typically ran faster as the race progressed whereas all able-bodied sprinters progressively slow down as the race goes on. As the writer puts it, sprinters all try to slow down as slowly as possible. The reason Pistorius got faster, though, was that he could not assume the sprinter's crouch for the start and so could not explosively respond to the starter's gun. Lacking an ankle, it simply took him longer to accelerate to top speed, but once he got there it took him less energy to maintain it.

To be fair to Pistorius, since he lost his lower legs before he was a year old he certainly never knew all this during his running career. And it hardly matters now since his running career is almost surely finished for good.

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