Lie faceup on the floor and place your lower legs and heels on a Swiss ball. (A) Push your hips up so that your body forms a straight line from your shoulders to your knees. (B) Without pausing, pull your heels toward you and roll the ball as close as possible to your butt. (C) Pause for 1 or 2 seconds, then reverse the motion, by rolling the ball back until your body is in a straight line. Lower your hips back to the floor.