The Teres Major is a muscle of the upper limb, playing a part in the complex movements of the shoulder joint. It is a thick, somewhat flattened muscle, often described as rectangular or ovoid in shape. This muscle is among the seven scapulohumeral muscles, which are those that connect the scapula (shoulder blade) to the humerus (upper arm bone), facilitating various arm movements and contributing to shoulder stability.
Its Precise Position
The Teres Major muscle is situated in the shoulder region, extending from the posterior aspect of the scapula to the humerus. It originates from the dorsal surface of the inferior angle of the scapula. From this origin, its fibers travel superolaterally, converging into a flat tendon. This tendon then inserts onto the medial lip of the intertubercular groove of the humerus, also known as the bicipital groove.
This muscle lies just below the infraspinatus and teres minor muscles. It is also positioned superior to the latissimus dorsi muscle. The Teres Major contributes to the formation of the posterior wall of the armpit (axilla) and its lower border forms part of the posterior axillary fold.
Its Role in Movement
The Teres Major muscle is a significant contributor to several movements of the arm at the shoulder joint. Its primary actions include adduction, extension, and internal (medial) rotation of the humerus. Adduction involves bringing the arm closer to the body, while extension moves the arm backward from a flexed position. Internal rotation causes the arm to rotate inward, towards the trunk.
This muscle often works in synergy with the larger latissimus dorsi muscle to perform these actions. For instance, in activities like swimming, rock climbing, or throwing, both muscles cooperate to produce powerful arm movements. The Teres Major also plays a role in stabilizing the humeral head within the glenohumeral joint.
Distinguishing It From Similar Muscles
The Teres Major muscle is often discussed alongside the Latissimus Dorsi and Teres Minor muscles due to their proximity and sometimes similar functions. It is frequently referred to as the “lat’s little helper” because its actions closely mirror those of the Latissimus Dorsi. Their tendons are closely related at their insertion point on the humerus, and sometimes their muscle fibers can even be fused.
Despite its name and location near the Teres Minor, the Teres Major is not considered part of the rotator cuff muscles. The rotator cuff consists of four muscles—supraspinatus, infraspinatus, teres minor, and subscapularis—which primarily stabilize the shoulder joint and facilitate rotation. The key difference is that the Teres Major does not attach to the capsule of the glenohumeral joint, unlike the Teres Minor and other rotator cuff muscles.