CNN Sanjay Gupta MD November 3, 2013 12:52:00
Ankle is less likely to land in front of the knee. >> because not reaching. >> what that does for every action is equal opposite reaction. if you hit the ground with your foot going forward, the ground will push you back and slow down. >> youre hitting the brakes. >> you have to put more effort to reaccelerate your body after it decelerates. secondly, when you hit out in front, your knee will be more straight and ankle will be pointed upward and you stiffen your leg and you hit the ground harder...
Source: archive.org