What it does: Works the abs, buttocks, back, and thighs.
 
 How to do it: Lie on your back with your feet on top of the ball, knees bent, hands resting by your sides. Press down into your heels, toes up, and lift your lower back (relax your neck). Roll the ball away to form a straight line from shoulders to heels. Contracting your abs, bend your knees to draw the ball back in. Don’t lower your buttocks to the floor until you finish your reps.