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What To Do: Three sets of 12 to 15 reps.
Target Muscles: infraspinatus, teres minor, posterior deltoid
Set Up: Lie on your right side with a light dumbbell in your left hand, upper arm tight to your side with your hand pointing toward the ground, elbow bent at 90 degrees [A].
Action: Keeping contact between your body and your upper arm, slowly rotate your shoulder until your forearm is perpendicular to the ground [B]. Maintain a 90-degree angle in your elbow as you move. Slowly lower and return to the start. Repeat, and when your set is finished, lie on your left side and repeat on your opposite shoulder.