The Anatomy of the Pectoralis Major Muscle

The pec major is a chest muscle that moves the shoulder

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The pectoralis major is a large muscle in your chest that helps to move your shoulder. You have two pectoralis majors; one on each side of your body. The pecs, as they are commonly referred to, help to pull your arm across the front of your body. Injury to the pectoralis major may cause shoulder pain and limit your ability to fully use your arm.


The pectoralis major is a fan-shaped muscle in the front of your chest wall. It consists of two heads. The clavicular head originates from the front side of your medial clavicle, or collar bone. It then courses out to your humerus (upper arm bone) and attaches at the intertubercular sulcus of the bone.

The sternocostal head of the pectoralis major originates from your sternum, the upper six costal cartilages, and the external oblique muscle. It travels towards your arm and attaches to the humerus with the clavicular head of the pec muscle.

The pectoralis major muscle is innervated by the brachial plexus. The upper part of the muscle is innervated by the lateral pectoral nerve from cervical level five, six, and seven. The lower part of the pec is innervated by the lateral and medial pectoral nerve from cervical five, six, seven, and thoracic level one.

Blood supply to the pectoralis major is via the pectoral branch of the thoracoacromial trunk.

The pectoralis major is superficial and can easily be seen and palpated. Simply place one hand on the front of your shoulder and slide it in towards your breastbone. The large muscle in the front of your chest is the pectoralis major. It resides underneath some fatty tissue in men or the breast tissue in females.


The pectoralis major adducts your arm. That means it pulls your arm across the front of your body. Is also works with the subscapularis muscle, a rotator cuff, to rotate your arm in.

When your arm is fixed or bearing weight, the pectoralis major works with your latissimus dorsi and other scapular stabilizers to elevate your body. This is important during crutch-walking and when pushing.

During forced respiration or heavy breathing, the pectoralis major is active to help elevate your chest and ribs. This allows your lungs to fully expand to get air in and out of your body.

Associated Conditions

The most common injury to the pectoralis major muscle is a tear of the tendon near the shoulder joint. This occurs when a force is applied to the muscle that overloads the tendon, and most pec injuries occur during heavy weightlifting. The resulting force tears the tendon.

There are three grades of pectoralis muscle tears. Grade I is a simple overstretching of the tendon. A grade II strain occurs when the tendon is overstretched and is partially torn. A full thickness tear of the pectoralis tendon is classified as grade III and is considered the most severe of the pec tendon tears.

Symptoms of a pectoralis major tear may include:

  • Pain in the front of your shoulder
  • An audible pop sound when the injury occurs
  • Difficulty moving your arm inwards or across your body
  • Swelling in the front of your shoulder
  • A visible or palpable divot in the front of your shoulder
  • Bruising in your chest or upper arm

If you suspect you have a pectoralis major rupture, you should see your physician right away. He or she can diagnose your condition and help you get the proper treatment for your injury.

An injury to your shoulder joint may also cause problems with your pec major. A rotator cuff tear may place excessive stress through your pec, and a frozen shoulder may adaptively shorten your pec muscles and cause limited motion there.

A pinched nerve in your neck may cause injury to the nerve the innervates your pectoralis major. This may cause weakness or paralysis of the muscle.

Sitting with a forward head and rounded shoulder posture may place your pectoralis major muscles in a shortened position. This may make standing and sitting upright difficult and limit shoulder range of motion.


Proper treatment of pectoralis major injuries requires an appropriate diagnosis of your condition. If you suspect you are having a problem with your pec, see your physician right away.

For pectoralis major ruptures or tears, you must initially rest. This allows the tendon to heal properly. A sling may be worn to help keep your shoulder and arm in an optimal position for healing. Your rest period will vary based on the severity of your injury but most often lasts for two to four weeks.

After a period of rest and immobilization, you may begin light movement of your arm. This gently stretches your pec muscle and improves mobility around the tendon. Working with a physical therapist to learn the right exercises for your pec injury is a good idea. Gentle shoulder range of motion exercises may be started, and using shoulder pulleys to improve mobility can help restore shoulder and arm mobility. The corner pec stretch may be done as well. A towel may also be used to stretch the pecs.

Gentle loading of the pec muscles may also be a part of the rehab of a pec tear. Shoulder internal rotation with a weight or resistance band may be started to gradually increase the load-bearing tolerance of the injured muscle. Progress should be done slowly, and full strength should be achieved before attempting a dumbbell or barbell chest press.

Keep in mind that everyone progresses differently after a pectoralis major rupture. Before starting any treatment for your pecs, check in with your PT or physician.

If a pinched nerve is causing your pectoralis major weakness, you must first get pressure off the nerve. Pinched nerves most often come from your spine as the result of a bulging disc or spinal arthritis. Your PT can show you exercises to help free the nerve. Once it is no longer pinched, work can be done to gradually strengthen your pecs using resistance bands, body weight, or dumbbells.

Shoulder injuries that may cause pectoralis tightness may require you stretch both the shoulder and your pec muscles. Your PT can help you improve shoulder range of motion and get your shoulder (and pectoralis major) functioning normally again.

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