Five 15-Minute Workouts

The Dynamic Push-Up

What it does: Strengthens the arms, chest, abdominals, backs of thighs, and buttocks.
 
 How to do it: Lie on the ball. Place your hands on the floor in front of you, shoulder-distance apart. Bend both elbows into a push-up and raise your legs. Straighten your arms, then lower your legs, and push off with your arms until your feet touch the floor, toes turned out. Move into The Frog.