Pectoralis Major
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The chest muscle (clavicular and sternal portions); its primary action is horizontal adduction (flexion) of the arm — a powerful action.
Detail
The pectoralis major has clavicular and sternal portions. The clavicular fibers run in a direction similar to the anterior deltoid; the sternal fibers are more horizontal (Thompson, 1989). Its function is horizontal adduction (flexion) — drawing the arm from the side-horizontal position to the front-horizontal position, a powerful action. Origin: inner half of the anterior surface of the clavicle, anterior surface of the costal cartilages of the first six ribs, and adjoining portion of the sternum. Insertion: a flat tendon 2 or 3 inches wide to the outer lip of the intertubercular groove of the humerus.
Pectoral training notes: the primary movement is horizontal adduction (flexion); secondary movements are shoulder-joint flexion and adduction. ROM is not determined by how far the weight moves — determine the user's ROM first. For upper pecs, 25 to 30 degrees is a good training angle. Scapular adduction is essential to increase the force angle (2-joint muscle). It is essential to initiate the exercise by pectoral contraction, not deltoids or arm movement. There is no separate "upper" or "lower" muscle — consider fiber positioning/arrangement. Exercises: bench press, incline bench press (MEO clavicular pectoralis), flyes, pec deck, and cross-over cable (body parallel to floor).
Key facts
- Two portions: clavicular (fibers like anterior deltoid) and sternal (more horizontal fibers).
- Primary action: horizontal adduction (flexion) — powerful; secondary: shoulder flexion and adduction.
- Origin: inner half of anterior clavicle, costal cartilages of first 6 ribs, adjoining sternum.
- Insertion: flat tendon (2–3 in wide) to outer lip of intertubercular groove of the humerus.
- Upper pec training angle: 25–30°. Scapular adduction increases force angle.
- Corroborated by independent EMG literature: a ~30° incline produces the greatest clavicular (upper) pectoralis activation among tested incline angles (e.g. Lauver, Cayot & Scheuermann, 2016) — consistent with the founder's 25–30° figure.
Connections
- horizontal-flexion-adduction — primary action.
- scapular-movement — scapular adduction aids pec work.
- anterior-deltoid — assists; similar clavicular fiber direction.
- bench-press / incline-bench-press / chest-fly — training exercises.
- pectoral-rotation-bar-placement — ROM safety in chest training.
Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.