The Teres Major is a thick, rectangular muscle located in the posterior shoulder region that plays a significant role in controlling the movement of the upper arm. As one of the seven scapulohumeral muscles, it acts as a powerful connector between the shoulder blade and the upper arm bone. Understanding the function of the Teres Major is important for anyone interested in shoulder health, athletic performance, or general upper body strength. This muscle contributes heavily to many pulling movements, making it an integral part of the shoulder girdle’s mechanics.
Anatomical Placement
The Teres Major muscle is situated on the back of the torso, immediately below the Teres Minor and Infraspinatus muscles. Its origin point is the posterior surface of the inferior angle of the scapula, the bottom tip of the shoulder blade. It inserts onto the medial lip of the intertubercular groove of the humerus, the upper arm bone. From its origin, the muscle fibers travel upward and laterally, wrapping around the humerus.
The Teres Major is often referred to as “Lat’s Little Helper” because it runs parallel to the much larger Latissimus Dorsi muscle and shares a common insertion point. The muscle receives its neural signals from the lower subscapular nerve, which branches from the brachial plexus (C5-C7).
Primary Functions of the Muscle
The Teres Major is a prime mover of the shoulder joint, responsible for three distinct actions of the humerus. These actions include shoulder adduction, which involves pulling the arm down toward the side of the body from an elevated position. This movement is utilized in activities like swimming the butterfly stroke or pulling a rope down.
The muscle also performs internal, or medial, rotation, turning the arm inward toward the midline of the body, such as when reaching behind the back. It also acts as an extensor of the shoulder, pulling the arm backward from a raised position in front of the body. The combined force of these three actions allows the muscle to generate significant power for pulling and throwing motions.
Distinguishing the Teres Major from the Rotator Cuff
A common misconception is that the Teres Major is part of the rotator cuff, likely due to its name similarity with the Teres Minor. The four muscles of the rotator cuff—Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis—share a defining characteristic: their tendons attach to the capsule of the shoulder joint for dynamic stabilization. The Teres Major does not attach to this joint capsule, instead inserting lower down on the shaft of the humerus. This makes it a powerful mover rather than a primary stabilizer of the shoulder joint.
The Teres Major and the Latissimus Dorsi are considered synergistic muscles because they perform the exact same three primary movements: adduction, extension, and internal rotation. Their combined action is essential for powerful movements like chopping wood or performing a chin-up. This close partnership reinforces its role as a force generator rather than a fine-tuner of the shoulder joint.
Strengthening and Activation
Targeting the Teres Major is accomplished through exercises that involve pulling the arm down or back toward the body. Any rowing variation, such as the bent-over dumbbell row or the seated cable row, effectively engages the muscle by focusing on retracting the shoulder blade. Lat pulldowns are also highly effective, especially when using a supinated, or underhand, grip, which enhances activation.
Another specific exercise is the cable straight-arm pulldown, where the arm remains extended and pulls the cable down from an overhead position. Regularly strengthening this muscle promotes better posture and contributes significantly to the overall stability of the glenohumeral joint. This improvement aids performance in sports that require throwing or swinging.