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The Biomechanics of Speed

Isn't that a cool picture? That's Olympic Silver Medalist Justin Gatlin (Peter Bohler snapped the shot), the second fastest man in the world. My book the Body Builders focuses on how scientists and bioengineers are finding new ways to hack into the human body and rebuild it. But those same technologies are also helping some of us to become Bigger, Stronger, Faster and Smarter (in fact that was going to be the title of my book at one point, until Charles Duhigg beat me to it!).

One of coolest stories I have written in recent months grew out the reporting for the first chapter of my book (which also features the famous rock climbing double amputee prosthetics-building genius Hugh Herr). Last spring, I flew down to Florida and spent the day hanging out with U.S. Olympic sprinter Gatlin, his coach Dennis Mitchell and a sprint biomechanics guru name Ralph Mann. They were trying to use technology to beat Usain Bolt. And it almost worked, though in the end at Rio Gatlin had to settle for second place.

The first thing I learned is that when we run, our legs act like giant springs. We bounce like basketballs or pogo sticks. So it's not always the best idea to take long strides -- especially straight off the starting blocks. Sometimes you want to minimize air time. Notice how Justin Gatlin is almost horizontal to the ground in the pic above, like a bullet, yet his feet are just inches from the ground? Credit Ralph Mann for that. Gatlin's goal is to pound his feet into the ground as many times as possible in the beginning to gather extra bounce and power in his step. Scientists have known for decades that our ligaments are built to absorb, store and release elastic "recoil" energy when we run. In fact, about 35 percent of the power output in each stride is recycled energy. The goal off the blocks is to rev up that power as fast as possible. You can't do that if you are bursting forward, with long strides and in between them your feet are spending a lot of time in the air.

Mann is himself a former Olympic medalist -- he was a hurdler. Check him out in 1972.

Since retiring, he has spent years reverse engineering the biomechanics of sprint (and hurdle) speed by slowing down video of the world's fastest individuals, and precisely measuring how all the different parts of the body move in relation to one another. From that, Mann has designed what he calls a "performance model."

Speed is simple, Mann likes to say. There are primarily two components: the number of strides a runner takes each second and the length of those strides. Each comes at the expense of the other, and a coach has to decide which to emphasize. That's where Mann's performance model comes in. Its algorithms are calibrated to produce the maximally efficient ratio, based on body type and a whole host of other variables, including race length, the length of different limbs in relation to one another, and overall height and weight.

If you want to know more about how it works, you can read more about it in the cover story I wrote for Popular Mechanics here.

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