What is the primary function of the infraspinatus muscle?

The infraspinatus muscle is primarily responsible for the rotation of the shoulder joint. It is one of the four rotator cuff muscles, which play a crucial role in stabilizing the shoulder and allowing for a wide range of motion. Specifically, the infraspinatus muscle is situated on the posterior aspect of the scapula and its fibers run laterally to attach to the greater tubercle of the humerus. When this muscle contracts, it facilitates lateral or external rotation of the humerus at the shoulder joint.

The other muscle functions mentioned, such as flexing, extending, or adducting the shoulder joint, are primarily associated with different muscles in the shoulder region. For example, flexion is largely performed by the pectoralis major and the deltoid, while extension is also contributed by muscles like the teres major and latissimus dorsi. Adduction, on the other hand, is primarily achieved through the pectoralis major and latissimus dorsi, rather than the infraspinatus. This focused role on rotation distinguishes the infraspinatus from these other functional movements of the shoulder.