I have yet to see any study done on riders with flexible arches, what I call flat feet. On the upstroke, the foot doesn't do much but on the down stroke, the foot does a flexing routine. As we all know, flexing of a frame is not efficient. The power transfer is somehow reduced. I think the same thing for the flexing of the foot. Orthotics try to keep the arch in the arch position. But with a flat footed rider, the arch support does very little when pressure is applied on the down stroke. The arch still collapses and the result is flexing.

The original poster talked about getting more power from the pedal stroke. The article that NOS88 shows doesn't address the arch itself and how it flexes. I have experimented with my particular pedal stroke style. At slow speeds it doesn't matter much. At higher velocities when I want to maintain speeds say above 20 mph, then it does matter. What I do is to cup my arch to keep it stiff so as not to allow it to flex. To do that, I am slightly in a toe down position.