Out of all resistance training exercises, push-ups likely have the
most variations. Using the stability ball to put your feet not only makes
the push-up more of a core exercise, it changes the emphasis from the lower
pec muscles to the upper pec muscles. The primary use of Swill ball pushups
with the feet on the ball is going to be for those with general fitness
goals which include strengthening the core and chest muscle group.
Since the stability ball pushups use your body weight for resistance,
they are not going to increase the strength as much as heavy resistance
exercises such as the bench
press will. If your primary fitness goals are increasing strength
push-ups on stability balls may be good at the beginning of your workout
program but will take a back seat to adding resistance with free weights or
cables as you advance.
Perhaps the best use of any body weight exercises on stability balls are
with core exercise programs or beginner strength programs. The push-ups may
also be used later on in a chest workout as one of the final exercises you
use if "going for the burn" is how you like to work out.