ASPeed - The Biomechanics of Running
The importance of proper foot position during ground striking.
When sprinting, the foot should strike the ground directly underneath; or ideally, a little bit behind the body's center of gravity. There are several reason for this. One reason is momentum. In order to use the body's natural momentum to our advantage the ground strike needs to occur behind the center of gravity. That way we can continue to drive the knees underneath our body. Looking at the overstriding picture in the video, you can see that the lower body is forced to create its own momentum by pulling the upper body along rather than letting the body fall forward and letting gravity create the momentum. The extra pulling responsibility placed on the lower body during overstriding also puts a lot of stress on the hamstring and puts one in jeopardy of pulling a muscle. Another reason the foot should strike the ground under or behind the body's center of gravity is leverage. When sprinting, we want apply force to the ground using triple extension (extension of the ankles, knees, and hips). The way to achieve the proper leverage for this triple extension is keep the ground strike under or behind the center of gravity. This will ensure a good shin angle in relation to the ground, let the foot to hit the ground in dorsiflexion, and allow force to be applied to the ground using all of the muscles in the lower body from the hips down.