It works the quads, calves, and glutes. Hold the ball behind you and stand so that the ball is pressed between your back and the wall. Place your feet in front of your body about hip distance apart. The center of the ball should be against the lower back. Keep in contact with the ball and lower your body by bending your knees until your upper thighs are parallel to the floor. Hold down there for one to two seconds and then return to your start position.