"Sprinters must compress and release in a forward directon, I don't see how they can compress virtically,but perhaps they do?"
A sprinter's body is inclined forward in the direction of motion when he is down on the starting thingy. Hence a compression along the length of the body will have a forward component. But as a dancer you cannot afford to have a strong incline into the direction of motion - you may have a strong incline against the direction of motion, be vertical, or a very miniscule incline into the motion in a few select settings (tipsy, etc)