Pectoralis Major

Latin: Pectus = Breast

OriginClavicular head - Medial 1/3 of the clavicle, Sternal Head - Sternum, Costal head - 2nd -6th or 7th ribs, abdominal fibers - superficial aponeurosis of the external oblique and rectus abdominis
Insertion: Crest of the greater tubercle of the humerus (lateral lip of the bicipital groove
Action: 

  • all fibers - adduct, medially rotate and horizontal adduction of the humerus, protraction of the scapula
  • upper fibers - flex the humerus
  • lower fibers -  depress the shoulder girdle, and extend the arm from a flexed position
  • Innervation: innervated by the medial and lateral pectoral nerves, spinal nerves C5 - C7 supply the lateral nerve and C8 - T1 supply the medial nerve. 

Much of society suffers from the stress that modern day work, places on them.  Many hour spent in a car during a long commute added upon time spent in front of a computer and then again commuting back home again.  This can lead to a posture that is detrimental to the thoracic spine, neck, shoulders and arms.  Pectoralis major can become a major player in a slumped forward shoulder posture that can lead to poor body mechanics and gait patterns which will lead to a stiff thoracic/cervical spine and shoulder dysfunction.  Complaints can often be of pain or stress in the upper back between the shoulder blades, back of the neck, difficulty in breathing and chest pain that can mimic heart problems.  Trigger points can refer into the 1st through 3rd finger, the anterior shoulder and create a depressed protracted shoulder along with internal rotation of the humerus. 

Pectoralis major usually does not entrap nerves, but the subclavius, which depresses the clavicle can entrap the brachial plexus causing numbness or thoracic outlet syndrome.  This also makes the release of pectoralis major and subclavius important when addressing cervical neck/cranial issues because of the attachment of the sternocleidomastoid on the clavicle.  If tension remains on the clavicle from pectoralis major and subclavius then getting SCM to release will have limited results.  One important thought to remember is that the shoulders can affect the neck and visa-versa the neck can affect the shoulders.  So addressing the shoulders and the cervical spine as a functional unit is a good rule of thumb when working with shoulder our cervical/cranial issues.

The lymph vessels that supply the tissue in the pectoral area can sometime become blocked by muscular tightness and restrict lymph drainage from the area.  Loosening pectoralis major can help with poor lymphatic drainage in the area and decrease edema. 

It is important to understand that pectoralis major has three heads that can pull the humerus into different positions.  The clavicular head can depress the clavicle.  The sternal, clavicular, and costal heads will internally rotate the humerus.  The costal head (lower fibers) will also pull the shoulder into a depressed position and protract the shoulder.  When these muscles work together they can create a powerful force and lock a person into internal rotation and depressed shoulders. 

Other muscles that should be examined are latissimus dorsi, teres major, anterior deltoid, subscapularis, pectoralis minor and serratus anterior.  These muscles are synergistic in many of the actions of pectoralis major and assist in the forward depressed shoulder position.  Also, whenever a depressed shoulder is present checking the rectus abdominus on the ipsilateral side is a good idea because of it fascial connection to pectoralis major.  If a rotation in the torso is present, an anterior shoulder and anterior contralateral hip, checking the external oblique and internal oblique is helpful in addressing a rotation. 

When working with any condition it is important to check downstream and upstream from the area of the symptom.  If only the area of concern is addressed the result will be limited.  Have fun working Pectoralis Major and all of it's accomplice!

Let me know your thoughts, ideas, concerns or complaints.  I hope that this can be a useful resource and I encourage positive response and any corrections if you see the need for any.  Thanks for reading!