Acting together, the two heads of the pectoralis major flex, adduct, and medially rotate the arm at the glenohumeral joint. The clavicular head flexes the arm from an extended position, whereas the sternocostal head extends the arm from a flexed position, particularly against resistance.
The pectoralis major is innervated by the lateral and medial pectoral nerves, which originate from the brachial plexus in the axilla.