Which muscle located on the back and involved in extending and adducting the arm?

• A. Pectoralis Major
• B. Latissimus Dorsi
• C. Trapezius
• D. Deltoid

Answer: (B)

Identifying the back muscle responsible for arm extension and adduction. The latissimus dorsi is a broad muscle of the back that inserts on the humerus. Its main actions are extending the arm (moving it backward), adducting the arm (pulling it toward the body), and medially rotating the arm. This combination fits a muscle located on the back that extends and adducts the arm, making it the best match. The other muscles have different primary roles or locations: pectoralis major is in the chest and mainly flexes and adducts the arm; trapezius moves the scapula and supports shoulder girdle movements rather than directly extending/adducting the arm; deltoid surrounds the shoulder, with the middle fibers primarily abducting the arm and the other fibers contributing to flexion or extension in different contexts.