The pectoralis major is a large, fan-shaped muscle that spans the front of the upper chest, divided into a clavicular head arising from the collarbone and a broader sternal head originating from the breastbone and rib cartilages. Both heads converge into a single flat tendon that attaches to the humerus, making it the primary muscle for horizontal pressing movements and bringing the arm across the body. Because the two heads have partially independent nerve supplies and different fibre orientations, they can be emphasised selectively by changing the angle of a pressing movement.
| Origin | Medial half of the anterior clavicle; Anterior surface of the sternum and costal cartilages of ribs 1–6 |
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| Insertion | Lateral lip of the intertubercular groove of the humerus |
| Nerve Supply | Lateral pectoral nerve (C5, C6, C7); Medial pectoral nerve (C8, T1) |
| Blood Supply | Pectoral branch of thoracoacromial artery; Perforating branches of internal thoracic artery |
| Actions | Adduction and internal rotation of the arm; Flexion of the arm to 90°; Extension of the arm from a flexed position |
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Its main mechanical roles are horizontally adducting and internally rotating the arm at the shoulder, the motions required during pushing, throwing, and most chest exercises, with the clavicular head contributing more to arm elevation and the sternal head more to arm depression from an overhead position.
The pectoralis major is among the most frequently injured muscles in strength athletes, with ruptures almost always occurring at the distal tendon during heavy eccentric loading on a bench press. Tightness in this muscle is also a common driver of rounded shoulder posture, anterior shoulder impingement, and thoracic kyphosis, making pectoral stretching a routine component of shoulder rehabilitation programmes. Weakness or inhibition, sometimes occurring after prolonged immobilisation or breast surgery, typically shifts pressing load to the anterior deltoid and triceps.
With the arm elevated to around 90° and the elbow slightly bent, ask the subject to push horizontally against resistance, the muscle belly becomes palpable across the entire anterior chest from the clavicle down to the fifth or sixth rib, and the distal tendon is easily felt just medial to the arm at the anterior axillary fold.
A complete or partial tear of the distal tendon at its humeral insertion, typically occurring during an eccentric overload on a bench press, producing a sudden audible pop, immediate weakness, bruising tracking down the inner arm, and a visible bulge of the muscle belly toward the chest.
Muscle fibre tears ranging from minor (Grade I) to complete disruption (Grade III), most often at the musculotendinous junction, caused by excessive loading during pressing or fly exercises and presenting as localised pain, swelling, and reduced pressing strength proportional to the grade.
Inflammation of the costal cartilage at the sternal attachment of the pectoralis can mimic a muscle strain but typically worsens with direct sternal pressure or deep breathing rather than resisted arm movement, and is common in high-volume pressing athletes.
