The researchers are Peter G. Weyand and Rosalind F. Sandell (both from Southern Methodist University, Dallas, Texas), Danille Naomi Leoni Prime (Rice University, Houston, Texas), and Matthew W. Bundle (University of Wyoming, Laramie).
They showed in their study that several variables limit the maximum running speed of humans.
And, the researchers beieve that we haven't reached that peak speed yet.
They conjecture that, based on their research, the biological limits of how fast humans can run could be raised from nearly 45 kilometers per hour (28 miles per hour), today's top speed, to, what they estimate, to be 56 kilometers per hour (35 miles per hour) or even 40 miles per hour (sometime in the future).
The summary of their research is published in the Journal of Applied Physiology.
Its title is “The biological limits to running speed are imposed from the ground up” (Appl Physiol (January 21, 2010); doi:10.1152/japplphysiol.00947.2009).
They state in the abstract to their paper that running speed is determined (and limited) by the mechanical interaction “... between the stance and swing phases of the stride.”
The researchers “… tested whether stance phase limitations are imposed by ground force maximums or foot-ground contact time minimums.”
Page two continues.
The U.S. researchers compared various types of movements (gaits)—hopping on one leg and running backward—to running forward.
The researchers took precise measurements of the forces applied to the treadmill’s surface with each contact of the foot, and with the three different types of gaits.
Dr. Wevand (an associate professor of applied physiology and biomechanics at the SMU Annette Caldwell Simmons School of Education and Human Development), one of the authors of the study, stated, "The prevailing view that speed is limited by the force with which the limbs can strike the running surface is an eminently reasonable one.” [EurekAlert.org: “New study: Human running speeds of 35 to 40 mph may be biologically possible”]
He adds, "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.” [EurekAlert.org]
Wevand continues to state, “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." [EurekAlert.org]
They found that some of the variables imposing running limits on humans are “force limit,” or the amount of force applied by the foot to the ground, and “contact time,” or the amount of time in which the foot applies a force to the ground.
Page three concludes.
The amount of time that the foot contacts the ground for the world’s fastest sprinters is less than one-tenth of a second.
That peak force occurs at the very instant the foot hits the ground.
The researchers found that the ground forces applied by the leg muscles to the ground at “maximum speed” during one-legged hopping on one leg are over 30% greater than the ground forces applied during forward running.
And, they also found that the forces generated by the active muscles within the legs are about 1.5 to 2.0 times greater in the one-legged hopping than in the forward running at all speeds lower then maximum speed.
Dr. Bundle (an assistant professor of biomechanics at the Wyoming College of Health Sciences), another author of the study, states, "The very close agreement in the briefest periods of foot-ground contact at top speed in these two very different gaits [one-legged hopping and forward running] points to a biological limit on how quickly the active muscle fibers can generate the forces necessary to get the runner back up off the ground during each step." [EurekAlert.org]
The EurekAlert article concludes, “The researchers said the new work shows that running speed limits are set by the contractile speed limits of the muscle fibers themselves, with fiber contractile speeds setting the limit on how quickly the runner's limb can apply force to the running surface.”
Based on evidence that ground forces are greater in one-legged hopping than in forward running, the researchers concluded that humans can run faster than they are currently running.
Bundle adds, "Our simple projections indicate that muscle contractile speeds that would allow for maximal or near-maximal forces would permit running speeds of 35 to 40 miles per hour and conceivably faster.” [EurekAlert.org]
They conclude (from the abstract of their paper): “… that the stance phase limit to running speed is imposed, not by the maximum forces that the limbs can apply to the ground, but rather by the minimum time needed to apply the large, mass-specific forces necessary.