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 arm forward and downward—for example, in swimming, hitting, or throwing overhead.

The teres major is particularly active when maintaining position of the upper extremity. This static activation is common in computer work, driving, or other activities where the arm is held steady in a given position. Fatigue from prolonged positioning may lead to adhesions, chronic pain, hypertonicity, ischemia, and trigger points in the posterior shoulder and particularly the teres major. The area of muscle convergence in the posterior axillary fold is commonly tender and ischemic, and contains numerous trigger points. Targeted manipulation and active movement (such as the cat/cow pose) can help flush the tissue, decrease pain, and restore function.

Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009). Contact her at functionalbook@hotmail.com.

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