Which back muscle inserts on the humerus to move the arm?

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

Answer: (A)

The movement in question is about a back muscle that directly attaches to the upper arm bone to move the arm. The latissimus dorsi is a large back muscle that inserts on the humerus, specifically at the intertubercular groove. This placement lets it pull the arm downward and inward, providing actions like extension, adduction, and medial rotation of the shoulder. That direct insertion on the humerus is why it’s the best answer for a back muscle that moves the arm.

The other muscles mentioned don’t fit this role. The pectoralis major attaches to the humerus as well, but it’s a chest muscle, not a back muscle. The trapezius and rhomboids act on the scapula, moving the shoulder blade rather than inserting on the humerus to move the arm itself.