What is a Rotator Cuff?

 John Voelz, Doctor of Physical Therapy

Lots of people talk about their “rotator cuff,” but what exactly is a “rotator cuff?” The rotator cuff is an arrangement of muscles and tendons that holds together the inherently unstable shoulder joint (also known as the “glenohumeral joint)

Notice below the “ball-and-socket” formation of the glenohumeral joint……..this is where your arm attaches to the shoulder complex, which includes the shoulder blade (scapula). The second diagram shows how easily this type of joint can become dislodged, or “dislocated.”


These X-Rays show an actual example of a dislocated shoulder joint. Notice how the arm has slipped below the rest of the shoulder complex. In this case, the arm would have to be pulled forcefully then slid back into the socket in order to relocate it. Repositioning a dislocated shoulder is extremely painful.


Because this “ball-and- socket” joint can easily slip out of place, something must be there to hold it together ……especially during movements that challenge the joint, like reaching up high or throwing a ball.




The diagram below/left (red arrows) shows the need for some set of forces to hold the joint together. This is the job of the rotator cuff. Four muscles make up the rotator cuff, and together, they “grab onto the arm” and “hug” the joint together, keeping the ball portion firmly in the socket portion.


Along with protecting the shoulder joint and keeping it intact, the rotator cuff helps with inward (internal) and outward (external) rotation. These motions are important for many things, but most commonly we use them for reaching behind our head (external rotation) and reaching behind our backs (internal rotation). RotatorCuff05



These two activities put great strains on the rotator cuff because they force the shoulder joint into rapid internal rotation and rapid external rotation, straining the limits of the joint. A baseball pitch and tennis overhead smash actually take the shoulder ball-and-socket joint into extreme external rotation then rapid acceleration into extreme internal rotation. The rotator cuff has to work extra hard throughout and beyond a safe range of motion. Without proper training, these motions can result in torn rotator cuff muscles.

Here are some great exercises to help strengthen the rotator cuff



Watch this excellent video animation of the anatomy, kinesiology, and biomechanics of the shoulder complex.


Next week I’ll go into different problems associated with the rotator cuff.

If you’d like to learn more ways to strengthen your rotator cuff, please stop in!

karinWhat is a Rotator Cuff?

Comments 1

  1. D Lowe

    very interesting video! do you have a similar video of the elbow? Son-in-law dislocated elbow playing baseball & has complete tear of UCL. would love to understand it better as Dr opted for no surgery.

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