Which muscle abducts the shoulder?

• A. Supraspinatus
• B. Latissimus Dorsi
• C. Subscapularis
• D. Serratus Anterior

Answer: (A)

The muscle that initiates shoulder abduction is the supraspinatus. It sits in the supraspinous fossa and runs under the acromion to attach to the greater tubercle of the humerus. When it contracts, it pulls the humeral head into the glenoid and lifts the arm through the first roughly 15 degrees of abduction, acting as the starter before the deltoid takes over for the higher range.

Other muscles in the mix: latissimus dorsi and teres major mainly contribute to extending, adducting, and medially rotating the humerus rather than abducting. Subscapularis medially rotates the arm. Serratus anterior helps upwardly rotate and stabilize the scapula to permit full arm elevation, but it is not the primary shoulder abductor at the glenohumeral joint.