[quote author="dbandre" date="1210440478"]The angular momentum about the hip is slowed before ground contact, therefore the foot, shank, and leg are being decelerated before ground contact. Speed here would actually inhibit leg stiffness during ground contact as rapidly occurring changes in muscle-tendon lengths cannot produce as much force as one’s near resting states. My point about length-tension relationship remains valid from this point of view.
Angular momentum would decrease because the moment arm decreases as the leg straightens and comes under the hips. It’s likely not a direct result of the foot slowing down as you suggest. Mann’s data over the past 20 years also corroborates this. In fact, it’s his data on elite sprinters that says that one of the defining characteristics of better sprinters is that they have greater negative / backward foot speed relative to the ground.[/quote]
deceleration doesn’t mean there is not any backwards speed, just it’s reducing and having greater backwards speed doesn’t suggest it is not decelerating as well. I can’t feasibly see a generating of greater leg stiffness with a leg that is moving at 3 joints that is still moving at significant speeds. The cross bridges in the muscles just don’t support force output with rapidly changing lengths in muscles which has to occur with extension of both hip and knee joints prior to ground contact, but the subsequent movements of those joints at ground contact require the greatest force generating capabilities to maintain enough leg stiffness to maintain speed and the ROM at ground contact is minimal. It shouldn’t be surprising that faster athletes can develop more force at a greater lengthening speed less faster athletes.
I already discussed that transference directly to sprinting is likely minimal for squatting. Most adaptations from squatting still need to be trained specifically into the skill of sprinting, likely suggesting a lag, this is a motor control/learning problem not strength problem. Granted I cannot provide research and I just don’t have the time gather all my sources that led to believe this, but I can speculate on this.
As far as a EMG and joint data study, just look to the Wiemann NSE Study from 1995, I know it’s old and joint data is semi positional in a qualitative sense, but EMG data suggests a greater role for hamstrings than gluteals.