I probably don't have the physiology quite correct here but the thing is Mike its all well and good developing or aspiring to develop a huge upper body physic by doing all of these pressups, but think of all the O2 that is needed to keep it fired up. As an ex Climber with over developed upper half and a puny set of legs (arms like legs) I'd much rather now when running have my blood supply go mainly to my legs than be diverted to my arms!