Lie facedown with your torso on the ball, place your hands on the floor, raise your legs, and walk your hands out until just your thighs are on the ball (A). Squeeze your glutes and walk out until you're in the plank position, with just your feet on the ball (B). Pull your abs in tight to keep your body stable. Hold for five seconds, then walk your hands back to the starting position. That's one rep. Do a total of 10 to 15 reps.