if you train to exhaustion, wouldn't you automatically be training for maximum stimulation? i understand that fatigue doesn't make muscles grow, that it's the work involved. but those last pushups push the muscles just a bit harder. just a different way of describing the same act i reckin. however, i don't know enough about muscle growth to dispute or claim any training over another.
on another note, saying that a muscle works as one unit would work for a muscle with only 1 insertion point and 1 origion like the bicep. however, i know for damn sure that i can work and flex my pec in different ways to stress the upper, middle, lower, inner, and outer parts. the origion point of the pec major is the clavicle, sternum, and cartilage of the top 6 ribs (this is a wide area from sternum to edges of cartilage. it includes many seperate strands of muscle with the thicker, outer strands connecting on the cartilage).
could we say that each strand can only be worked as one long chain? each strand flexes the fibers in a certain order. on my pec the outside strands contract maximally first to bring my arm in. once my arm is in the outer pec strands have less leverage, but the inner pec strands have more. therefore, i would say that a cable fly forces more strands to contract in the center chest for the mere purpose of efficiency and range of motion- my arms are closer to the center line. my conclusion is that the chest can be worked in different areas depending on the range of motion, and leverage incidental to the angle of the work because it is has a large area of origion.
whew. that took a while to put into words!!