Which muscles contribute to upward rotation of the scapula as part of a force couple?

Which muscles contribute to upward rotation of the scapula as part of a force couple?

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

Answer: (D)

Upward rotation of the scapula during arm elevation comes from a force couple: muscles pulling in different directions on the scapula so the result is rotation rather than sliding. The group of upper trapezius, lower trapezius, and serratus anterior work together to rotate the scapula upward. The upper trapezius helps lift the scapula, the serratus anterior pokes the medial border forward and the inferior angle laterally and upward, and the lower trapezius pulls the medial border downward while contributing to the rotation. Together these actions tilt the scapula so the glenoid fossa faces more upward, allowing the arm to lift smoothly. Other choices don’t produce that upward-rotating couple. Rhomboids and levator scapulae tend to retract and elevate the scapula, which counters upward rotation, while pectoralis minor protracts and depresses, opposing the upward tilt. Latissimus dorsi mainly drives humeral movements and can contribute to downward rotation of the scapula, not the upward rotation needed here.

Upward rotation of the scapula during arm elevation comes from a force couple: muscles pulling in different directions on the scapula so the result is rotation rather than sliding. The group of upper trapezius, lower trapezius, and serratus anterior work together to rotate the scapula upward. The upper trapezius helps lift the scapula, the serratus anterior pokes the medial border forward and the inferior angle laterally and upward, and the lower trapezius pulls the medial border downward while contributing to the rotation. Together these actions tilt the scapula so the glenoid fossa faces more upward, allowing the arm to lift smoothly.

Other choices don’t produce that upward-rotating couple. Rhomboids and levator scapulae tend to retract and elevate the scapula, which counters upward rotation, while pectoralis minor protracts and depresses, opposing the upward tilt. Latissimus dorsi mainly drives humeral movements and can contribute to downward rotation of the scapula, not the upward rotation needed here.