Originally Posted by
livedarklions
The question is whether that energy is returned to the chain when the BB "unflexes" in the direction of the foot that's not exerting force on the pedal.. I don't know the answer to that and people who seem to know a lot more about the subject than I do disagree.
it is definitely not obvious. You could potentially model it in FEA, but even that would be an estimate at best. Modern frames are certainly modelled in FEA, but probably not to the degree of attempting to quantify anything more than lateral, vertical and torsional flex and resultant stress distribution across the frame. Frames like the Specialized Aethos have probably been subject to the most analysis in this regard.