Which muscle is a prime mover for scapular abduction?

Which muscle is a prime mover for scapular abduction?

• A. Posterior deltoid
• B. Latissimus dorsi
• C. Serratus anterior
• D. Trapezius

Answer: (C)

Scapular abduction, or protraction, is the motion of moving the scapula forward along the rib cage. The serratus anterior is the prime mover for this action because its fibers attach to the ribs and the anterior (inner) surface of the scapula, so when it contracts it pulls the scapula's medial border forward and against the thoracic wall, effectively protracting the scapula and helping with upward rotation as the arm elevates. Other muscles listed don’t do this primary protraction. The posterior deltoid mainly moves the arm at the shoulder, not the scapula. The latissimus dorsi largely extends, adducts, and internally rotates the humerus and can depress the shoulder girdle but isn’t the primary protractor. The trapezius has roles in elevating, retracting, and upwardly rotating the scapula, but it isn’t the primary muscle that moves the scapula forward.

Scapular abduction, or protraction, is the motion of moving the scapula forward along the rib cage. The serratus anterior is the prime mover for this action because its fibers attach to the ribs and the anterior (inner) surface of the scapula, so when it contracts it pulls the scapula's medial border forward and against the thoracic wall, effectively protracting the scapula and helping with upward rotation as the arm elevates.

Other muscles listed don’t do this primary protraction. The posterior deltoid mainly moves the arm at the shoulder, not the scapula. The latissimus dorsi largely extends, adducts, and internally rotates the humerus and can depress the shoulder girdle but isn’t the primary protractor. The trapezius has roles in elevating, retracting, and upwardly rotating the scapula, but it isn’t the primary muscle that moves the scapula forward.