The pectoralis (pec) minor muscle is the often forgotten little brother of the pectoralis major muscle. Like many little brothers, it can cause problems far beyond its size.
The pec minor is a small thick muscle found underneath the pec major near the shoulder. Unlike his big brother, the pec minor does not attach to the arms, rather it attaches from the mid front rib cage to the front of the shoulder blade.
The pec minor’s job in life is not to move the arms, but to provide stabilization for the shoulder blade and assists with pulling the shoulder blade forward. When you pull yourself out of the pool using your arms, you are activating your pec minor muscle to stabilize the shoulder.
This ability to both rotate and pull the shoulder blade means the pec minor is a major player with posture – both good and bad posture.
The typical bad posture of hunching with the shoulders rolled forward is perpetuated thanks to the pec minor. Sitting in this posture for prolonged periods day after day leads to the pec minor shortening into this position causing the muscle to be tight and hyper-responsive.
Ultimately, when someone does attempt to hold their shoulders back in the correct position, a tug-of-war is created between the postural muscles in the back and the tight pec muscle in the front.
This abnormal position of the shoulder has a spillover effect on other shoulder muscles. The muscles on the back and top of the shoulders, the levator scapulae and trapezius muscles, now have to work harder to support shoulder movements. Eventually this results in chronically tight neck and shoulder muscles with multiple trigger points (“knots”).
Individuals who sit for prolonged periods will be particularly at risk for developing this presentation. Often, desk workers will mistake “stress” in their upper shoulder for these fatigued tight muscles.
There are many possible causes of a tight pec minor muscle. Bad posture is certainly at the top of the list for most people. However, direct trauma to the chest, stress, prolonged use of crutches, or a heavy backpack carried over the shoulder will also do the trick.
A tight pec minor muscle can affect the movement patterns of the shoulder joint and cause shoulder injuries. Probably the most common side effect of a shortened minor muscle is loss of space in the subacromial arch.
The subacromial arch is the space in the shoulder under the joint between the collar bone and the shoulder blade. In this space there is an important rotator cuff tendon and bursa which can be compressed with arm movements, particularly overhead movements.
The pec minor has one more little dastardly little trick up its sleeve – it can cause pain and altered sensation into the arms. It achieves this directly through vessel compression (both nerve and blood) and indirectly through formation of trigger points.
A tight pec minor can compress the nerves and blood vessels that travel from the torso into the arms. This is one possible cause of a condition called Thoracic Outlet Syndrome. In this presentation, compressed nerves cause pain into the nerves. It is a situation similar to how compressed nerves in the low back can cause sciatica in the legs.
Although less common, it is also possible to compress the blood vessels that travel from the shoulder to the arm.
The pec minor is also prone to forming painful trigger points. These trigger points also have the ability to cause pain in the arms.
When activated, the trigger point of the pec minor can radiate pain in the front of the shoulder and across the chest. The radiating pain can even extend all the way down the arm to the pinky, ring and middle fingers.
Of course, most people experiencing chest pain with pain radiating down their arm to the hand think “heart attack” not “pec minor.” When we have these types of heart attack symptoms not due to an underlying heart problem, it is often termed “pseudo-angina.” For the average person it can be very difficult to differentiate between pseudo-angina and an actual cardiac infarction. Due to the potential fatality associated with a heart attack, it is important to quickly receive a proper diagnosis from a cardiac doctor before dismissing chest pain as due to a muscular condition.
Surprisingly, some individuals who have had a cardiac event continue to have chest wall pain and arm symptoms due to activation of the pec trigger points.
Happily, like all troublesome little brothers, the pec minor responds to a little attention and TLC. Treatments such as chiropractic adjustments to the thoracic spine, deep tissue release, ball rolling, dry-needling and stretching can make a noticeable improvement in a short period of time. Of course treatment needs to be partnered with actual postural changes.
The pec minor is a little brother that does not like to be ignored. Ignore him and you run the risk of developing chest pain, arm pain, rotator cuff tendonitis, shoulder bursitis, trigger point formation, neck/upper shoulder stiffness, and loss of mobility in the shoulder. Your chiropractor will design a treatment program for you that will address your unique presentation.
Dr. Jemal Khan is a chiropractor based in the Cayman Islands.