[Kontact]

Originally Posted by Mark McM

I'm not sure how you conclude that. Take, for example, the cases where the cranks are vertical (one pedal is at the top of the stroke, and one pedal is at the bottom). In this position, the differential between the right/left down forces on the pedals is maximum, which results in the maximum (torsional) frame flex. Due to the torsional rotation at the BB, the bottom pedal is at the maximum downward deflection, and the top pedal is at the maximum upward deflection. As the pedals continue to rotate through the next 180 degrees, the right/left force differential reverses, and the deflections also reverse. In other words, as the pedal rises at the back of the pedal circle, the reversal of the deflection acts to raise the pedal. Until the frame returns to its neutral, unflexed position, the stored energy in the frame is indeed helping to lift the rear leg.

Curiously, the torsional flex at the BB has an interesting affect on the shape of the pedal 'circle'. Instead of moving in a perfect circle, the upward and downward deflections cause the shape to be stretched into an ellipse. I wonder what affect this has on muscle utilization?

The problem is, this isn't true. The maximum frame deflection is during the power stroke, somewhere around 3 o'clock. The frame isn't flexing because we are stepping on it, it if flexing because we are trying to move the rear wheel so hard that tension in the chain is enough to pull the BB off center.