Which muscle abducts the arm?

• A. Pectoralis major
• B. Brachialis
• C. Pectoralis minor
• D. Deltoid

Answer: (D)

Abduction of the arm is the movement that lifts the upper limb away from the body at the shoulder joint, in the frontal plane. The deltoid, especially its middle fibers, is the primary muscle responsible for this motion across a wide range of motion, pulling the humerus upward and outward to raise the arm. The pectoralis major does the opposite actions at the shoulder (adduction and inward rotation), while the pectoralis minor and brachialis don’t move the arm in abduction—one stabilizes the shoulder blade and the other flexes the elbow. It’s also worth noting that the supraspinatus assists with the initial abduction, but the deltoid provides the main, sustained lifting beyond that early phase.