Lie facedown on a fitness ball, with both hands on the floor. Walk your hands out, allowing the ball to roll beneath your body until it is under your shins. Your hands should be directly below your shoulders, so it looks like you’re ready to do a pushup. Keeping your torso straight and your abs contracted, bend your elbows and lower your chest toward the floor. Stop when your upper arms are parallel to the floor. (A) Return to start, and immediately contract your glutes as you lift your right leg off the ball. (B) Lower your right leg to the ball, then lift the left leg. That’s one rep. 8 to 12 reps
Make the move harder by placing the ball under the tops of your feet. Make it easier by keeping the ball under your knees.