Which muscles act as a force couple to rotate the scapula upward?

Which muscles act as a force couple to rotate the scapula upward?

• A. Rhomboids and levator scapulae
• B. Upper trapezius, lower trapezius, and serratus anterior
• C. Pectoralis minor and latissimus dorsi
• D. Serratus anterior alone

Answer: (B)

Upward rotation of the scapula during lifting the arm is produced by a force couple made by the upper trapezius, lower trapezius, and serratus anterior. The upper fibers of the trapezius pull the top of the scapula (the acromion) upward, while the lower fibers pull the inferior angle upward and outward. Serratus anterior keeps the medial border from pinching toward the rib cage and pulls on the medial border from the side, helping rotate the scapula upward as the arm rises. When these forces act together, they rotate the scapula upward around the thorax, allowing the glenoid fossa to tilt upward and the arm to elevate effectively. Other muscles don’t form this upward-rotation force couple. Rhomboids and levator scapulae tend to elevate and adduct the scapula, producing downward rotation rather than upward rotation. Pectoralis minor depresses and tilts the scapula forward, and latissimus dorsi mainly contributes to humeral movements rather than scapular upward rotation. Serratus anterior alone can protract the scapula, but without the opposite pull from the trapezii, it doesn’t produce the full upward rotation; the coordinated action of all three is what creates the effective upward rotation.

Upward rotation of the scapula during lifting the arm is produced by a force couple made by the upper trapezius, lower trapezius, and serratus anterior. The upper fibers of the trapezius pull the top of the scapula (the acromion) upward, while the lower fibers pull the inferior angle upward and outward. Serratus anterior keeps the medial border from pinching toward the rib cage and pulls on the medial border from the side, helping rotate the scapula upward as the arm rises. When these forces act together, they rotate the scapula upward around the thorax, allowing the glenoid fossa to tilt upward and the arm to elevate effectively.

Other muscles don’t form this upward-rotation force couple. Rhomboids and levator scapulae tend to elevate and adduct the scapula, producing downward rotation rather than upward rotation. Pectoralis minor depresses and tilts the scapula forward, and latissimus dorsi mainly contributes to humeral movements rather than scapular upward rotation. Serratus anterior alone can protract the scapula, but without the opposite pull from the trapezii, it doesn’t produce the full upward rotation; the coordinated action of all three is what creates the effective upward rotation.