What is the action of latissimus dorsi?

• A. Extends, adducts, and medially rotates the arm; helps in drawing the trunk upward when the arms are fixed
• B. Abducts the arm
• C. Flexes the forearm
• D. Laterally rotates the arm

Answer: (A)

The main idea is that latissimus dorsi acts to move the arm in three ways at the shoulder: it extends the arm (pulls it back), adducts the arm (pulls it toward the body), and medially rotates the arm (rotates inward). It’s also capable of helping to pull the trunk upward when the arms are fixed, as in climbing. This combination of actions—extending, adducting, and internally rotating the humerus—matches the described function precisely.

Abduction of the arm is performed by other muscles like the deltoid and supraspinatus, not by latissimus dorsi. Flexing the forearm is done by muscles such as the biceps brachii and brachialis. Lateral (external) rotation of the arm is carried out by muscles like the infraspinatus and teres minor.