Which muscle mirrors the latissimus dorsi?

• A. Latissimus dorsi
• B. Trapezius
• C. Serratus anterior
• D. Pectoralis major

Answer: (D)

Muscles that move the shoulder in similar ways from opposite sides of the torso are often seen as mirror partners. The latissimus dorsi is a powerful shoulder mover that pulls the arm down and back, creating adduction and internal rotation (and it can extend the arm from a flexed position). The pectoralis major, located on the chest, performs a very similar action on the humerus: it brings the arm toward the midline and rotates it inward, with the clavicular and sternocostal parts contributing to different ranges of flexion and flexed-to-middle positions. Because they sit on opposite sides of the body and produce comparable shoulder-internal-rotation and adduction actions, the pectoralis major serves as the mirror to the latissimus dorsi. The other muscles listed have different primary roles (scapular movement or different shoulder actions) and don’t mirror latissimus dorsi in the same way.