The rotator cuff is not a muscle

(Last Updated On: July 23, 2021)

In my post on the anatomy of the IT band I mentioned the band is consistently talked about like it’s a muscle, when in fact it is a band comprised of multiple muscles.

It’s not a muscle; it’s made of muscles.

The rotator cuff is similar.

The rotator cuff is not a muscle; it is a group of muscles. 

Specifically, the rotator cuff is made up of the:

-Supraspinatus

-Subscapularis

-Teres minor

-Infraspinatus

These muscles do NOT all perform the same function. In fact, the subscapularis (internal rotator of the humerus) and the infraspinatus / teres minor (external rotators) actually perform opposite functions.

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The distinction between the cuff muscles and their function is a very, very important one to make.

Here is why:

I consistently find people talking about “training the cuff.” Along this vain I’ll read how we all need to train our cuff to stabilize the humerus in the glenoid fossa.

If we are training stability then this implies we have too much mobility, right? Let’s go with that theme and see where it takes us.

Typically, when it comes to the humerus being hypermobile, it’s either in the anterior or superior direction. The humerus travels too far forward or too far upward; too often. And here it’s important to mention a joint is just about always hypermobile in one direction. Not ALL directions. Using the humerus again, the joint may be hypermobile (I guess we can say “lacking stability” for relatability) in the anterior direction but hypomobile (not enough mobility aka “too much stability”) in the posterior direction.

Let’s go with the anterior hypermobility, as this is more common. (For all those who get pain at the bottom of a bench press, humeral anterior glide is why.)

What’s going on with the rotator cuff in anterior glide (a common reason for shoulder pain)

I wrote quite a bit about the muscular imbalances in this issue in Best exercises for the subscapularis, I’m going to use some of the info from that post.  

Often times the tight/overactive muscles in this case are pectoralis major and latissimus dorsi. This is because the subscapularis (remember- a cuff muscle) isn’t internally rotating the humerus like it should be. So, other internal rotators, like pec major and the lat, pick up the slack.

The subscapularis also depresses the humeral head. Because the humeral head is shooting so far forward we have a clear indication the subscapularis isn’t depressing the humerus like it should be. (Ah, that humeral stability we’ve been hearing about.) Because of this, the infraspinatus and teres minor pick up the slack as depressors.

One thing I didn’t go over in that post was indicators the infraspinatus and teres minor were overactive. I’ll use a stretch everyone always references: The Sleeper Stretch

Before someone asks, no, I don’t use this stretch, at all. I don’t think Eric (pictured) does anymore either.

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When dealing with the sleeper stretch it’s common for people to let their scapula wing / anteriorly tilt / move, and or humerus glide too far forward, in order for them to get their arm down.

So, many people -rightfully so- mention the need to eliminate these factors, and then you realize how little you can actually internally rotate your arm.

What I never see anyone write about is why, when done correctly, a person suddenly has such little motion. Yeah, yeah, “the posterior capsule is tight, bro.” What about the muscles at play here?!

If we’re internally rotating the humerus that means we’re stretching the external rotators, right? And what externally rotates the humerus? The infraspinatus and teres minor -rotator cuff muscles.

This is why when performing the sleeper stretch properly you suddenly have such little range of motion (some know this as glenohumeral internal rotation deficit (GIRD)): You’re now putting the humeral external rotators on stretch, and they’re tight.

Also, now you know why the scapula tends to wing on people when their arms internally rotate (like in the sleeper stretch). Where do the infraspinatus and teres minor start?

The middle to the medial border of the scapula i.e. These muscles can pull on the humerus AND the scapula.

Thus, so many people who present humeral anterior glide also have scapular winging.

Here’s an example. Notice the right humeral head gliding forward and the right scapula winging. It gets progressively worse as the video goes on:

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Hence, in my subscapularis exercise post I wrote:

Therefore, when strengthening the subscap we want to pick exercises that elicit great activity in the subscap, but don’t elicit much activity in pec major, lat, infraspinatus, and teres minor. 

In actuality, part of the shoulder is TOO tight / rigid / stable / whatever, and part of the shoulder is too mobile. Thus, “stabilize the shoulder” is NOT a solution.

Going with this, part of the rotator cuff is too tight / rigid / stable, while part of the cuff is not active enough. Thus, “strengthen the rotator cuff” is NOT a solution.

Because what’s advocated for one muscle of the cuff is contraindicated for another.

This is my long way of saying any declarative statements to the tune of “You need to train your cuff son” is incomplete. And probably said by someone who doesn’t understand what they’re doing.

What direction is unstable? What muscles are long? What muscles are weak? WHICH rotator cuff muscle is long, weak, tight? Etc.

Context, context, context.

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