The infraspinatus muscle originates on the back of your shoulder blade and attaches to the back of your humerus -- upper-arm bone -- by a tendon. The infraspinatus muscle is the primary muscle that externally rotates your arm, turning it out and away from your body. In addition, the infraspinatus muscle moves your arm backward into extension, and away from your body into horizontal extension when your arm is held parallel to the ground.
Tight muscles move into a shortened position -- the ends of the muscle move closer to each other. A tight infraspinatus muscle pulls your arm into external rotation. To stretch this muscle, direct the force in the opposite direction -- into internal rotation. Place your right arm behind your back as if you are going to scratch it. Hold a broomstick in your left hand and bring it up over your left shoulder. Slide the stick down your back until you are able to grasp it with your right hand. Slowly pull the stick up toward the ceiling with your left hand, sliding your right hand up your back. Stop when you feel a stretch in the front of your shoulder -- without pain -- and hold this position for 20 to 30 seconds. Relax and repeat three times. Switch hand positions to stretch your left infraspinatus muscle.
The subscapularis muscle originates on the front of your shoulder blade and attaches to your upper-arm bone. The subscapularis muscle moves your arm into internal rotation -- turning your arm in toward your body. This motion is important for reaching behind your back to tuck your shirt into your pants. In addition, the subscapularis pulls the top of your humerus down as you raise your arm, keeping the ball part of your shoulder joint properly positioned in the socket. The subscapularis muscle is powered by the subscapular nerve.
Stretch your right subscapularis by applying gentle force into external rotation. Hold one end of the broomstick in your right palm with your forearm neutral -- thumb pointed toward the ceiling. Grasp the opposite end of the broom with your left hand in a palm-down position. Bend your elbows to 90 degrees and hold your right elbow tight against the side of your body. Slowly push the broomstick to the right with your left hand, rotating your right forearm out to the side until you feel a stretch in the front of your right shoulder. Hold this position for 20 to 30 seconds, then relax. Repeat three times. Switch hand positions and repeat to stretch your left subscapularis.
