Pectoralis major

The pectoralis major is a powerful chest muscle with three actions: adduction of the arm (bringing it toward the body's midline), flexion of the arm at the shoulder, and medial rotation of the humerus. It is most active during pushing movements such as bench pressing, as well as climbing and arm-swinging during running. The clavicular head contributes more to flexion, while the sternocostal head is more active in extension from a flexed position.

Poland syndrome is a rare congenital condition characterized by the absence or underdevelopment of the pectoralis major muscle on one side of the body, typically the right. It is often associated with ipsilateral hand abnormalities including shortened fingers (brachydactyly) or webbed fingers (syndactyly). The condition varies widely in severity and may also involve absence of the pectoralis minor and other chest wall structures.

Pectoralis major rupture most commonly occurs during heavy bench pressing when the muscle is under eccentric load at full stretch. It typically involves the tendon at its humeral insertion. Patients experience sudden sharp chest and arm pain, followed by bruising, swelling, and a visible or palpable defect in the anterior axillary fold. The anterior chest wall contour becomes asymmetric, and there is weakness in arm adduction and internal rotation.

The pectoralis major myocutaneous flap is a reconstructive surgical technique in which the pectoralis major muscle, along with its overlying skin and subcutaneous tissue, is used to fill tissue defects—most commonly after head and neck cancer resections such as laryngectomy or mandibulectomy. Its robust blood supply from the thoracoacromial artery makes it a reliable flap for covering large wounds or reconstructing the oral cavity and pharynx.

The pectoralis major inserts on the lateral lip of the bicipital groove of the humerus (also called the intertubercular sulcus). This insertion point allows the muscle to adduct and medially rotate the arm. The fibers twist 180 degrees before insertion, so the lower fibers of the sternal head end up above the upper fibers at the tendon—a design that increases the range over which the muscle can generate force.