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I t p a y s t o b e A B M P C e r t i f i e d : 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 51 FUNCTIONAL ANATOMY education Teres Major By Christy Cael The teres major is a muscle on the back of the shoulder that joins with the latissimus dorsi to form the posterior axillary fold. Compared to the latissimus dorsi, the teres major is much smaller and spans less distance. It has a specific origin on the inferior portion of the lateral border of the scapula, while the latissimus dorsi has a broad attachment on the trunk. This origin is just inferior to that of the teres minor, with the long head of the triceps brachii running between the two teres muscles. Both the latissimus dorsi and the teres major wrap around the humerus anteriorly and insert on the lesser tubercle and bicipital groove, with the teres major inserting slightly more posteriorly. Though they differ in size and shape, the teres major and the latissimus dorsi share all the same actions: extension, adduction, and internal rotation of the shoulder. The teres major is often called "lat's little helper" because of the strong functional association. It is a prime mover muscle and is most active when pulling the arm down and back from an overhead position or adducting the arm directly into the body when the scapula is fixed. Although the teres minor is located near the teres major, and has a similar shape, these muscles do not share functions. When the arm is fixed, the teres major and latissimus dorsi work together to pull the trunk toward the arm—for example, in pull-ups and climbing. When the arm is free, the teres major works with other shoulder internal rotators and extenders (the lower fibers of the latissimus dorsi, pectoralis major, and subscapularis) to pull the raised TERES MAJOR Attachments • Origin: Inferior lateral border of the scapula • Insertion: Medial lip of the bicipital groove on the humerus Actions • Adducts, extends, and internally rotates the shoulder Innervation • Lower subscapular nerve • C5–C6 Teres major