How fast can a human run?

When he runs, Usain Bolt — the fastest man that any of us have ever seen — maxes out at a top speed of 27.3 miles an hour. But scientists now believe we’re capable of running faster, perhaps as much as 40 miles per hour, if only we could increase the speed with which our muscle fibers contract.

Previously, it was thought that we were limited by the amount of brute force it takes to push our bodies off the ground, but the new findings are leading to speculation of ways to increase muscle contraction:

One option would be to increase the proportion of ultrafast 2X type muscle fiber, one of three types of mammalian muscle fibers. Studies have shown that athletes can slightly increase their 2X fibers by training intensely and then taking a break for a few weeks, he said.

Even this kind of training, however, wouldn’t let us catch a true speedster like a cheetah. Their four legged gait remains a much better way to run, if speed (and not endurance) is your ultimate aim.