How to do it: Sit on the ball, then walk your legs out so that your shoulder blades are resting on the ball, and your legs are at a right angle. Keeping your core tight, hold your arms straight out to your sides. Shuffle to the right until you feel your right shoulder blade come off of the ball, then shuffle to the left until you feel your left shoulder blade come off of the ball.
Reps: 6 on each side
What it works: Core, glutes, hamstrings, back, rear shoulders, and your proprioception