Shoulder Pain: Left Pec Major and Right Pec Minor Relationship

When it comes to shoulder pain and ribcage mechanics, nothing will gum up the normal mechanics of ribcage positioning – and thus shoulder health – like the dynamic duo of left pec major and right pec minor. But they aren’t ultimately to blame for their overbearing behavior. More on that later.

In the Right BC pattern, both muscles are attempting to pull us over to the left in a vain attempt to get our center of mass off the right foot.

But since our lumbar spine is oriented to the right in the left AIC pattern, our center of mass never truly moves over our left foot and thus the right pec minor and left pec major continue to pull, and pull, and pull some more. They won’t stop trying until you can truly get on your left side. 

Before I go further let me make clear that shoulder health is absolutely dependent on proper ribcage position. The scapula, half the shoulder joint, sits directly on top of the posterior aspect of the ribcage from about thoracic rib 2 down to about thoracic rib 7&8.

The ribcage is the foundation of all shoulder joint function and associated arm movements. 

If you don’t know what the right BC pattern is, I’d recommend watching this video for a visual understanding.

Right Pec Minor Dysfunction

The right pec minor attaches to the coracoid process of the right scapula and ribs 3,4, and 5.

Under normal circumstances it serves in scapular protraction/abduction/internal rotation. Basically it moves the scapula forward and down on the ribcage. This is a normal function of right arm swing during walking.

Under abnormal conditions the pec minor works as an accessory muscle of breathing, attempting to pull the right upper ribs *up* to facilitate airflow into the upper right ribcage. It does this because the right BC pattern results in a position of the ribcage that renders the left diaphragmatic practically useless as a breathing muscle and restricts the right side of the ribcage from expanding. 

The pec minor is thus recruited to help get more air into the compressed right upper ribcage that is restricted in expansion during inhalation due to the right BC pattern. If the ribcage can’t expand out, it will move up instead. This is obviously not ideal. 

Once the right scapula is forced to sit upon a right BC patterned ribcage for too long, muscle function changes and the right pec minor is constantly “on” because it’s put into a compromised position.

The right pec minor doesn’t get tight on its own accord!

It’s forced into that position by

  1. the mispositioned ribcage and
  2. the “disengaged-and-now-protracted-and-internally-rotated” right scapular position.

This is an important point to make. A tight pec minor is not a pec minor issue. It’s a ribcage/scapular issue that arose out of a body that is stuck in the right BC pattern, otherwise known as “right stance” phase of gait (walking).

A tight pec minor is only the symptom. 

And as we know, treating the symptoms, rather than the underlying cause, is a recipe for getting nothing accomplished long term. 

left pec major and right pec minor

Left pec major and right pec minor “attempt” to pull us to the left….and fail.

Left Pec Major Dysfunction

The left pec major has a dilemma. It knows it has to help rotate the sternum to the left, but it can’t quite get the job done. The right side of the ribcage is restricted and hasn’t “let go” enough to allow shifting of center of mass to the left, and the left pelvis below is still stuck in an anteriorly rotated position (left AIC pattern)

 In addition, the left arm internally rotates as a compensation for the position of the left scapula, which is externally rotated. This externally rotated scapula would under normal circumstances turn the left arm externally (away from the body) so that the arm stays congruent with the joint. But in our body’s attempt to stay straight, the left arm internally rotates, thereby ensuring the left pec major will stay overactive. 

As a result the left pec is conflicted. It knows it isn’t effective, but it has no say in the matter. If the position of the pelvis and the ribcage doesn’t shift to the left, the pec major can’t stop pulling. So while the left pec may be tight and restricting arm/shoulder movement, he is just as much the victim as the shoulder. 

The Solution

The normal response would be to stretch and/or massage both the right pec minor and left pec major. There is no harm in doing that, and you may get some short term relief, but it won’t solve anything in the long run.

Remember, we are talking about being stuck in a neuromuscular pattern called the left AIC/right BC pattern. This corresponds with being stuck in “right stance” phase of walking.

Until you can turn off the pattern and “re-learn” how to shift your center of mass to the left (left AF/IR) and establish a left ZOA, the right pec minor and left pec major muscles will never shut down completely.

They will only stop pulling when you actually get your center of mass to the left using the appropriate musculature. 

So the solution is re-positioning of the pelvis and ribcage so neutrality can be established. 

At that point you may realize that the right pec minor and left pec major are no longer “tight”. 

Once your body is neutral, sometimes you’ll find that these muscles truly are tight even after repositioning and establishing neutrality. You know this because the shoulders are restricted in simple range of motion tests when all the other tests look good. 

This situation indicates a true issue of muscle tightness rather than a “fake” tightness that was caused by a mispositioned ribcage and the way in that the arms/scapula compensated for it.

This “true” tightness can be problematic as it restricts full shoulder range of motion and function.

In that case, massage and stretching are appropriate because it is no longer an issue of position of the ribcage that is causing the muscular overactivity and tightness. It’s the vestiges of the old pattern that went on for too long.

Lengthening the tissue of the right pec minor and pec major is the way to go. 

Leave a Reply

Your email address will not be published. Required fields are marked *