FYI: What Is The Limit To How Fast A Human Can Run?

Peter Weyand, physiologist and biomechanist at SMU's Annette Caldwell Simmons School of Education and Human Development, talks about studying human speed.

By Jia You

The limit to how fast a human can run is 9.48 seconds for the 100-meter race, 0.10 seconds faster than Usain Bolt’s current world record, according to Stanford biologist Mark Denny. That is, if you are talking about natural human beings.
In a 2008 study published in the Journal of Experimental Biology, Denny modeled the fastest human running speed using records of men’s 100-meter race results going back to the 1900s. Denny plotted the annual best times in the race into a graph and used computer programs to come up with an equation whose curve best models the behavior of the actual graph he obtained. The curve showed humanly achievable time for the 100-meter race would level off at 9.48 seconds. “They haven't plateaued yet, but you can definitely see the data are bending a little towards that plateau,” Denny says.

There's been little improvement in the Kentucky Derby since the 1950s.Denny, who also modeled the best times for racing thoroughbreds and greyhounds in the same study, found there’s a speed limit for these races as well, with little improvement in the Kentucky Derby since the 1950s and dogs’ performances leveling off in the 1970s.

“If you look at other species — ones that we're trying to breed to run faster and faster — it's not working,” he says. “There's no reason to think that human beings are any different from the other species, that somehow these things don't have limits.”
Statistical models do not explain the mechanics behind running. So Peter Weyand, a biomechanics professor at Southern Methodist University, has taken a different approach to the question.

A leading expert in human locomotion, Weyand says the primary factor influencing speed is how much force sprinters hit the ground with their feet.
When athletes run at a constant speed, they use their limbs like pogo sticks, Weyand says. Once a sprinter hits the ground, his limb compresses and gets him ready to rebound. When he’s in the air, the feet get ready to hit the ground again.

When a runner hits the ground, 90 percent of the force goes vertically to push him up again, while only 5 percent propels him horizontally. In that regard, sprinters behave a lot like a super ball, Weyand says. “What they do is they bounce a lot,” he says.

Our body naturally adjusts how fast we run by changing how hard we hit the ground. The harder we hit the ground, the faster we go.

So just how hard can humans hit the ground while they run?...