Exercise Advice: Lie flat on your back on a mat with your feet flat on the ground and your knees bent. Grab a medicine ball with both hands and hold it on your chest. Push the small of your back down to the floor to isolate your ab muscles. Begin to roll your shoulders off the floor. Continue to push down with your lower back. Your shoulders should come up off the floor only about four inches, and your lower back should always remain on the floor. As always, make sure you let your abs do the work in a slow and controlled fashion!