Can you run even faster--maybe

[caption id="attachment_809" align="alignright" width="198" caption="Usain Bolt winning the men\'s 2008 Olympic 100m"][/caption]

How about 40 mph? A newly published study from the Journal of Applied Physiology suggests that the theoretical limit to human speed might run that high.

"Where once the maximum top speed of a human being was thought to be around 28 mph, a new study suggests that a trained runner could achieve speeds of 40 mph, or perhaps even more."

"The prevailing view that speed is limited by the force with which the limbs can strike the running surface is an eminently reasonable one," said Weyand, associate professor of applied physiology and biomechanics at SMU in Dallas.

"If one considers that elite sprinters can apply peak forces of 800 to 1,000 pounds with a single limb during each sprinting step, it's easy to believe that runners are probably operating at or near the force limits of their muscles and limbs," he said. "However, our new data clearly show that this is not the case. Despite how large the running forces can be, we found that the limbs are capable of applying much greater ground forces than those present during top-speed forward running."

In contrast to a force limit, what the researchers found was that the critical biological limit is imposed by time -– specifically, the very brief periods of time available to apply force to the ground while sprinting. In elite sprinters, foot-ground contact times are less than one-tenth of one second, and peak ground forces occur within less than one-twentieth of one second of the first instant of foot-ground contact.