What is the primary function of the biceps brachii?

The primary function of the biceps brachii is to flex the elbow and supinate the forearm. This muscle is located in the upper arm and has two heads that originate from the shoulder area. When the biceps contracts, it brings the forearm towards the shoulder (elbow flexion) and simultaneously causes the radius (one of the forearm bones) to rotate outward, which supinates the forearm – turning the palm upwards.

This dual action is particularly functional during activities that require lifting and rotating the forearm, such as doing a bicep curl or performing actions like turning a doorknob. The strength and versatility of the biceps make it essential for various upper extremity movements, contributing significantly to daily activities and exercises involving the arms.

In contrast, the other choices describe functions associated with different muscles or actions: extending the elbow is primarily performed by the triceps, stabilizing the shoulder involves a group of muscles known as the rotator cuff, and abducting the shoulder is primarily the function of the deltoid muscle. Thus, the choice that identifies the biceps brachii's role in flexing the elbow and supinating the forearm accurately represents its key function.