The Teres Major muscle is an important component of the shoulder girdle, a thick, flattened muscle. It plays a significant role in the mobility and stability of the arm at the shoulder joint. Commonly referred to as “the little Lat,” this muscle is frequently discussed alongside the Latissimus Dorsi due to their close functional relationship in powerful arm movements. Its primary function is to facilitate movement between the shoulder blade and the upper arm bone, allowing the arm to be pulled, extended, and rotated.
Where the Teres Major is Located
The Teres Major is situated on the posterior side of the torso, spanning the distance between the shoulder blade (scapula) and the upper arm bone (humerus). Its origin is primarily on the posterior surface of the inferior angle of the scapula. The muscle fibers course upward and forward toward the arm, inserting onto the medial lip of the intertubercular sulcus of the humerus, which is a groove on the front of the upper arm bone. This path, from the back of the shoulder blade to the front of the humerus, dictates its powerful pulling and rotational action. Unlike the Teres Minor, this muscle does not attach to the shoulder joint capsule and is not considered part of the rotator cuff.
The Three Primary Movements
The primary action of the Teres Major is to produce movement of the humerus at the glenohumeral joint (shoulder joint). It is responsible for three distinct motions: adduction, medial rotation, and extension of the arm. These actions allow for movements that involve pulling the arm toward or behind the body.
Adduction
Adduction is the movement that brings the arm closer to the midline of the body, such as pulling the arm down from an elevated position.
Medial Rotation
Medial rotation, also known as internal rotation, is the action of turning the front of the arm inward toward the torso. This movement is seen when the arm is rotated to tuck the hand into the small of the back.
Extension
Extension involves moving the arm backward, or posteriorly, away from the front of the body. The Teres Major is effective at this action when the arm is starting from a flexed or raised position.
Working Alongside the Latissimus Dorsi
The Teres Major and the Latissimus Dorsi muscles are functional partners, often earning the nickname “Lat’s little helper.” They share the same three primary actions on the shoulder joint: adduction, medial rotation, and extension. This shared function allows them to work together to generate substantial force. The muscles are physically close, with fibers running parallel before inserting near each other on the humerus, creating a synergistic unit. Their combined effort is responsible for strong pulling movements in activities like swimming, rowing, or climbing a rope, while the Teres Major assists in stabilizing the shoulder.
Injuries and Recovery of the Muscle
Injuries to the Teres Major muscle are rare, but they typically involve a muscle strain or tear. These injuries often result from sudden, forceful arm movements, particularly those involving overhead actions. Athletes in sports like baseball pitching, tennis, or swimming are at risk due to the repetitive stress placed on the muscle fibers. Recovery for an isolated strain is usually managed non-operatively, focusing on rest, reducing inflammation, and avoiding painful activities. Physical therapy is used in later stages to gradually reintroduce stretching and strengthening exercises, allowing a return to normal activity once mobility is restored.