Thoughts on knee position at the bottom of the stoke

To expound on my twitter.com comments about Lance. http://blip.tv/file/1431564

As the bottom of the pedal stroke, we have some interesting dynamics going on. Obviously, it is a weak aspect of the stroke compared to the down stroke. To produce here, force has to be applied as a effectively as possible.

Hip impact on force application at the bottom of the stroke:
This is the lowest point in hip action. The hip joint is transitioning from hip extension to hip flexion. If the hip actively flexes at the bottom of the stroke, it would produce a force that attempts to compress the crank. Since the crank cannot compress, this force has to be dampen by other joints and muscles or the activity will cause a shift in the rider center of gravity and therefore, a change in direction of the bike. If the hip actively attempts to extend at the bottom of the stroke, the effect would be stretching the crank. It would cause similar issues.

Ankle impact on force application at the bottom of the stroke:
Since the ankle is not a prime mover, it's positive impact has to do with translation of force and facilitation of proper position of the knee. If the ankle is actively flexing or extending at the bottom of the stroke, it causes similar effects as an active hip joint. But most notably, if the ankle is not positioned correctly, the knee cannot produce effective force from an effective position.

Knee impact on force application at the bottom of the stroke:
Here's the good news. Without the ability to utilize hip musculature or ankle muscular at the bottom of the stroke in a concentric manner, the knee becomes the solo prime mover. There are two key elements to being effective at this point in time: Knee angle and Knee position.
Knee angle is critically important if we are going to obey the rules of Length-Tension ratio
Knee position is critically important because the arc of motion of the knee must match the arc of the pedal as closely as possible. In this manner torque generated by knee flexion can move the pedal through the down stroke.

more on the effects of joints out of position in another post.