The muscles involved in the external rotation of your shoulder are the infraspinatus and teres minor. These muscles are two of the four that make up the rotator cuff. If they become injured, the inflammation can cause pain and restriction of movement when you attempt to externally rotate your arm. Physical therapy exercises can help reduce pain and restore mobility.
Standing Bar Exercise
Stand up straight with your feet hip-width apart. Hold a light barbell without weights or a broom handle with an underhand grip. Keep your arms at shoulder width and bend your elbows to a 90-degree angle. Your palms and fingers should face up. Keeping your elbows against your sides, push the bar as far to one side as you can. Push in the direction of the shoulder you wish to externally rotate -- for example, to rotate your right shoulder, move the bar to the right. Hold the stretch for two to five seconds. Work up to 10 repetitions.
Stand in a doorway and bend your elbow to 90 degrees. Place the opposite foot approximately 12 inches in front of the other. Raise your arm so your upper arm is in line with your shoulder and press your palm against the wall. Lean forward slightly, moving your torso away from your arm, until you feel a comfortable stretch. Hold for at least five seconds, working up to 90 seconds. This exercise can be painful if you have a serious rotator cuff injury or have recently had surgery, so ease into the forward lean. In the beginning, you might only be able to bend your torso slightly, but as your shoulder heals, you will be able to lean farther forward.
Lying-Down Weighted Exercise
Lie on the side opposite the shoulder you want to stretch. Bend your bottom elbow and place your forearm under your head. If desired, use a pillow between your forearm and head. Tuck a rolled-up towel between the armpit and elbow of your upper arm. Hold a light hand weight in your upper hand. Bend your upper arm 90 degrees. Without lifting your elbow, slowly raise your hand upward, then bring it back down so your palm faces your stomach. Repeat up to 10 times. If you are healing an injury, perform the exercise three times throughout the day.
Stand at a 90-degree angle to a wall and press your affected shoulder against it. Bend your elbow to 90 degrees. Keeping your elbow at your side and your palm open and facing out, press your forearm and the back of your hand against the wall. Hold the tension for five seconds and release. Repeat 10 times. If you are healing an injury, you might wish to perform this exercise up to three times throughout the day.