Peter Weyand, PhD, SMU. Locomotor Performance Laboratory.

From our new friend Peter Weyand, PhD, SMU, Dallas. Southern Methodist University, Locomotor Performance Laboratory.
In the study:
The biological limits to running speed are imposed from the ground up.
J. Appl Physiol (Jan 21, 2010).

Study concluded 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. So, the faster the foot applies the max force into the ground and gets that foot off the ground to do the same on the other foot, the faster the person will be able to run.