Which muscle primarily performs the action of internal rotation of the shoulder?

The latissimus dorsi is the muscle that primarily performs the action of internal rotation of the shoulder. This muscle is a large, flat muscle that covers the lower back and extends to the sides, attaching to the humerus (the bone of the upper arm). When the latissimus dorsi contracts, it pulls the arm down and in toward the body, facilitating internal rotation of the shoulder joint.

This muscle also contributes to other movements of the shoulder, including adduction and extension, but its role in internally rotating the shoulder is particularly significant during many activities like throwing or swimming. The mechanics of this muscle make it a central player in enhancing upper body strength and stability during movements that require internal rotation.

Other options listed, such as the pectoralis minor, primarily assist with protraction and depression of the scapula rather than acting as a major internal rotator of the shoulder. The hamstrings are a group of muscles located at the back of the thigh, serving functions related to bending the knee and extending the hip. The obliques, on the other hand, are involved in trunk rotation and lateral flexion, not shoulder internal rotation. Thus, the latissimus dorsi stands out as the main muscle responsible for this specific action