If your shoulders feel weak when you play racquet sports or toss a Frisbee, you may need to strengthen your rotator cuff muscles. This is a great exercise that will help to stabilize your arm in its socket.
1 Hold a dumbbell (2 to 5 pounds) in your left hand. Lie on your right side on the floor, or over a Bosu ball for comfort. Bend both knees. Position your left elbow at your side and bend your elbow at a 90-degree angle. Your palm and forearm will face your stomach.