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F r e e m u s i c d o w n l o a d s f o r C e r t i f i e d m e m b e r s : w w w. a b m p . c o m / g o / c e r t i f i e d c e n t r a l 41 FUNCTIONAL ANATOMY education Pectoralis Major By Christy Cael The pectoralis major is a large, superficial muscle that covers the chest from clavicle to abdomen. A complex network of muscle fibers extends centrally from the costal cartilage, sternum, and clavicle to a thickened convergence at the proximal humerus. Prior to inserting on the humerus, the fibers of the pectoralis major fold and twist, forming the thick anterior border of the axilla. The insertion is covered by the thick fibers of the anterior deltoid, making this portion difficult to palpate and a common site of adhesions and congestion. The pectoralis major has multiple segments with ascending, descending, and horizontal fiber directions. The upper or clavicular fibers are primarily utilized during flexion of the humerus. The middle or sternal fibers are utilized in conjunction with all other fibers for horizontal adduction. The lower or costal fibers are activated during extension of the humerus from a flexed or overhead position. The variation in fiber direction and broad span of this anterior muscle powers a wide variety of movements in front of the body, such as pushing, reaching, throwing, and punching, as well as a supportive role in forced inhalation. Adhesions between the various fibers and surrounding muscles can limit range of motion and circulation and perpetuate localized pain, trigger points, and postural dysfunction in the entire upper body. The pectoralis major has a distinct twist near its attachment on the humerus. This feature maintains leverage in the various positions possible at the shoulder. Fully flexing the shoulder unwinds the twist and prepares the muscle to extend and internally rotate the humerus. This is particularly PECTORALIS MAJOR Attachments • Origin: Medial clavicle, sternum, and costal cartilages of ribs 1–7 • Insertion: Lateral lip of bicipital groove of the humerus Actions • Internally rotates and horizontally adducts the shoulder • Flexes the shoulder (clavicular fibers) • Extends the shoulder from overhead position (costal fibers) • Adducts the shoulder from below shoulder height • Abducts the shoulder from above shoulder height Innervation • Medial and lateral pectoral nerves • C5–T1 Pectoralis major

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