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  Fitness > Sports Injuries >  

What Goes Wrong with Your Rotator Cuff
(also see 4 Exercises to Avoid and Rotator Cuff Tendinitis)

The rotator cuff consists of four muscles that run from the shoulder CUFFMUSL.JPGblade to the the upper arm, or humerus. Actually, physiologists think of the cuff as being the tendons of these four muscles—tendons are what connect muscle to bone—but from the perspective of preventing or rehabilitating shoulder injuries, it makes more sense to consider both tendons and muscles.

The four muscles of the rotator cuff are:

  • supraspinatus
  • infraspinatus
  • teres minor
  • subscapularis

In simple terms, these four muscles stabilize the shoulder. If, for some reason any of them can't do its job, major motions of the shoulder become impossible—forget throwing a ball, bench pressing, or even combing your hair!

Together, the four muscles of the healthy rotator cuff:

1. Counterbalance the upward pull of the deltoid muscle on the humerus

The deltoids are the major muscles responsible for raising your arms. Since they run downward from the collarbone to attach along the side of the humerus (upper arm), they would tend, when contracting, to pull the humerus straight up, jamming the top of the bone against the roof of the shoulder joint. Rotator cuff muscles prevent this by pulling the head of the humerus down just enough to prevent the collision and to allow the humeral head to move freely.

2. Externally rotates the shoulder

If you try to raise your arm with your thumb pointing down, you'll find you can only raise it about 80 or 90  degrees. (Sure, go ahead: try it.) This is the point at which the greater tubercle (a bony bump on the side of the humerus where various muscles are anchored) crowds the shoulder joint, impinging on the tendons and bursa that run there. Only by externally (or outwardly) rotating the shoulder are you able to raise your arm any higher. This external rotation is performed by two of the rotator cuff muscles.

3. Provide a stable base for the major motions of the shoulder joint

The dish-like socket of the shoulder joint is extremely shallow, and is stabilized by muscles and tendons surrounding it. The four muscles of the rotator cuff act like guy wires supporting a tent pole, each pulling from a different direction to hold the joint securely together while it's in motion.

4. Decelerate the arm when you throw something.

Throwing motions involve the cuff in two ways. First, throwing a ball is basically an attempt to throw your arm away from your body. The rotator cuff muscles, along with several others, prevent you from succeeding. Second, although throwing involves several actions at the shoulder, it really amounts to a case of high-powered internal rotation. It's the external rotators—the infraspinatus and teres minor—that put on the brakes at the end of the motion.

What Goes Wrong

If the cuff is damaged, it may not be able to perform the functions listed above. Many conditions, some mild, some severe, can keep the cuff from doing its jobs properly. Some of these include:

  • chronic degeneration
  • inflammation (various conditions ending in ``—itis")
  • calcium deposits
  • tears
  • impingement
  • joint contracture and adaptive shortening
  • muscle imbalance
  • fibrosis
  • injury

The Underlying Problem: Dysfunctional Shoulder Biomechanics

The most important thing to know about cuff injuries is that often the obvious injury—the tear, the inflammation, the fibrosis (all these terms are covered in The 7-Minute Rotator Cuff Solution)—simply represents the tip of the iceberg. The actual iceberg is dysfunctional shoulder biomechanics—basically, improper functioning of the joint. Dysfunctional shoulder biomechanics, brought about by repeated improper training, consists of a potpourri of conditions, including:

  • a muscle imbalance between the internal and external rotator muscles
  • adaptively shortened internal rotators (with possible scarring, called fibrosis, of tendons and muscle)
  • inflamed rotator cuff muscles (with possible fibrosis)

What You Can Do

To be effective, a rotator cuff program must address all the components that contribute to dysfunctional shoulder biomechanics. It must...

  • strengthen the external rotators
  • stretch the internal rotators
  • eliminate the training errors that promoted inflammation and started the ball rolling toward dysfunctional shoulder biomechanics in the first place

A program like this will be equally effective at rehabilitating the injured cuff and preventing injury in the healthy one.

- Also see 4 Exercises to Avoid
and Rotator Cuff Tendinitis


Baechle, Thomas (1994).  Essentials of Strength Training and Conditioning.  Human Kinetics, Nebraska.

Horrigan, J., Robinson, J. (1991)  The 7-Minute Rotator Cuff Solution.  Health for Life, LA, CA.

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