PLANK WITH SWISS BALL: Lie on stomach on top of ball, with feet resting on floor. Contracting abdominals, slowly move feet forward, rolling ball, until hands touch the floor. Use hands to continue forward walking motion, until feet raise off floor, and the back is in a straight line from shoulders to toes. Hold the pose for about 5 seconds, then release and walk hands back to comfortable position. Repeat 5 times.