What action does the supraspinatus perform before the deltoid takes over?

The supraspinatus is a muscle of the rotator cuff that plays a crucial role in the initiation of humeral abduction. This action involves the movement of the arm away from the body in the plane of the shoulder. Specifically, the supraspinatus assists in raising the arm by abducting the humerus until about 15 to 30 degrees of elevation. Once this initial movement is accomplished, the deltoid muscle takes over and continues to abduct the humerus to higher degrees.

Understanding this muscle's function is essential for recognizing its role in shoulder mechanics and stability. The other options refer to different movements that are not primarily initiated by the supraspinatus, which is why they do not capture the role of this muscle accurately in the context of shoulder abduction.