Which muscle assists in both internal rotation and adduction of the shoulder?

The latissimus dorsi is an important muscle that contributes to both internal rotation and adduction of the shoulder. It originates from the lower back and inserts into the humerus, allowing it to perform several motions. When the latissimus dorsi contracts, it pulls the arm towards the body and inward, facilitating adduction. Additionally, it rotates the arm internally when the shoulder is flexed, which is critical during various movements such as reaching across the body or during certain lifting actions.

Understanding the roles of various shoulder muscles is essential, as each contributes uniquely to shoulder movement and stability. While the pectoralis major also aids in flexion, adduction, and internal rotation of the shoulder, the question specifically highlights the dual role in internal rotation and adduction, where the latissimus dorsi's contributions are particularly significant. The deltoid primarily functions in abduction of the shoulder, and the supraspinatus mainly assists with the initial phase of abduction, neither aligning with the dual functions specified in the question. Thus, the latissimus dorsi stands out as the muscle best fitting the description of assisting in both internal rotation and adduction of the shoulder.