Your rotator cuff is a group of four small muscles--the supraspinatus, infraspinatus, teres minor and subscapularis--that form a literal “cuff” around your humerus, stabilizing it in the shallow shoulder socket.
Your rotator cuff is hard at work any time you move your shoulder, so don’t focus on training these muscles individually unless you’re directed to do so by a medical or fitness professional. Use a very light weight; you should be able to complete 20 to 30 repetitions before your muscles tire. Do not do these exercises if they cause pain.
Empty Can Exercise
Stand square with a small dumbbell in your right hand. Orient your right arm at a 45-degree angle to your body and turn your right hand thumb-down. It might help to imagine that you're emptying a can of soda just beside your right foot. Lift your straight arm up and out, maintaining the 45-degree angle to your body. Stop when your arm is almost level with your shoulder. Complete a full set, then repeat on the other side.
This exercise works your supraspinatus, which is primarily responsible for abducting your shoulder and stabilizing the shoulder blade. This muscle is the most commonly injured muscle in the rotator cuff. If the exercise causes pain, stop immediately; the pain may signal a rotator cuff injury.
Lie on your right side with a small dumbbell in your left hand. Bend your left arm at a right angle, tucking the elbow close against your side. Let your left forearm swing down against your body, then swing it back up to the starting position. Complete a full set, then repeat on the other side.
This works the infraspinatus. The infraspinatus externally rotates, transversely abducts and transversely extends your arm at the shoulder. According to ExRX, this is the second most frequently injured rotator cuff muscle.
Stop Sign Exercise
Stand square with a dumbbell in your right arm. Position your right arm as if you were going to do a shoulder press, elbow bent at 90 degrees, palm facing forward, weight directly above your elbow. Rotate your upper arm only, swinging your hand down to the “stop” hand signal. Allow discomfort to limit your range of motion; only rotate your arm as far as comfortably possible. Complete a full set, then repeat on the other side.
This exercise works the teres minor. Like the infraspinatus, the teres minor externally rotates, transversely abducts and transversely extends your arm at the shoulder.
Lie on your right side on a bench or table, gripping a small dumbbell in your right hand. Tuck your right elbow against your side just in front of your body, forearm sticking straight out in front of you. Rotate your upper arm so that your forearm swings up against your ribs. Lower your arm back to the starting position. Complete a full set, then repeat on the other side.
This works your subscapularis, which as the name indicates is located deep to your shoulder blades. The subscapularis internally rotates your arm at the shoulder.