Originally Posted by Towlie

No, they are pulling. Your quads are on top of your leg, right? They PULL your lower leg with respect to your upper leg to straighten your leg. That is exactly like triceps pulling to straighten your arm.

Your legs as a whole may be supporting or "pushing" your body upward, but that is quite different from saying that your quads are pushing -- muscles can't push, they can just pull. Think about a rope -- a rope can't push a car; it can only pull a car when in tension.