What is the main action of the supraspinatus muscle?

The supraspinatus muscle primarily functions to initiate arm abduction. It is one of the rotator cuff muscles and is responsible for helping raise the arm away from the body. The muscle's attachment point on the greater tubercle of the humerus allows it to exert a mechanical advantage during the early phase of abduction, facilitating movement up to approximately 15 degrees. After this initial movement, other muscles, particularly the deltoid, take over to continue the abduction process.

In contrast, other options listed do not accurately reflect the primary role of the supraspinatus. For example, flexion of the shoulder is largely attributed to muscles such as the biceps brachii and anterior deltoid. Adduction of the arm involves muscles that pull the arm toward the body, such as the pectoralis major and latissimus dorsi. Extension of the shoulder is mainly performed by muscles like the triceps brachii and posterior deltoid. Understanding the specific actions of each muscle is crucial for proper assessment of shoulder function and rehabilitation strategies.