Originally Posted by
livedarklions
It's totally beside the point anyway. The lifting of the leg doesn't generate much if any power because those muscles are evolved only to lift the weight of the leg. The muscles used on the downstroke are evolved to propel our entire weight when walking or running, and are therefore much more powerful.
He's got to explain how the leg goes from the bottom of the crank back up to the top without the use of any muscle power from either leg, and he can't do it sensibly, so he's pulling out this red herring.
I definitely agree that there is no meaningful power generated on the up-stroke. Enough studies of hundreds of elite cyclists have repeatedly shown that to be the case at normal cadence and higher power levels.
The weight of the leg itself does cancel out over a half-stroke. You are simply creating and releasing potential energy each time you raise and lower your leg. BUT you still have to expend energy in raising that leg (even if using the other leg to do it) even though you effectively get that energy back in terms of powering the bike forward. So having heavier legs raises your minimum energy expenditure required to pedal. It's no different to standing on the spot and raising your knee in the air and then letting it drop down again. It requires a minimum amount of energy (mgh) to lift your knee in the first place, even though that energy is released as you let it drop back down.
So in a way both of you have a valid point!