How Fast A Human Can Run?

Most People would say, the speed of Usain Bolt must be the highest acheivable speed by a human. Well you are close, according to Stanford biologist Mark Denny 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 (for natural human beings of course).

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.
In a 2010 study published in the Journal of Applied Physiology, Weyand and four other scientists had runners running on treadmills at a constant speed in different gaits –- running forward, backward, and hopping. Their study finds that when we hop, our limbs hit the ground with 30 percent more force than when we run, primarily because the foot stays much longer in the air. Based on that information, Weyand and his team calculated that in theory, human beings can run as fast as 19.3 meters per second — that is, if they hit the ground with the maximum force physiologically possible. If a sprinter were to run at that speed throughout the 100-meter race, he would finish in 5.18 seconds.
But that’s not the end of the story. In a new study to be published this year, Weyand and his team have found that maximizing running speed requires a tradeoff between hitting the ground hard and maintaining stride frequency. Hitting the ground with maximum force requires the sprinter to spend more time in the air, which slows down the strides he can make per second. The optimal combination of stride frequency and ground force varies with individuals depending on their size, leg length, and the speed they run, Weyand says. There is no golden ratio.
“We’re sort of moving into a Brave New World in athletics where there are many many different types of performance enhancement avenues available,” Weyand says. “What’s happening is that identifying what’s natural and what’s not natural is becoming increasingly blurry. To me, (to answer) what’s the ultimate speed somebody can run, we now have to go through a list of 10 different conditions: are we talking about no gene doping, no special technology, no pharmaceutical agents … But as we go further and further along there’s even potential for tracking shoe design to change speed. It starts to become a horribly complicated question.”

source: awescience.com