Which action is NOT performed by the biceps brachii?

The biceps brachii is a key muscle located in the upper arm, primarily involved in movements of the elbow and shoulder joints. Its main actions include elbow flexion, forearm supination, and to a lesser extent, aiding in shoulder abduction when the arm is raised.

Elbow flexion occurs when the biceps brachii contracts, pulling the forearm closer to the upper arm. Forearm supination is the action of rotating the forearm to turn the palm upward, which is also a primary function of this muscle. Additionally, while the biceps contributes to shoulder abduction, particularly when the shoulder is flexed, it does not directly perform this action as its primary function.

In contrast, elbow extension is the opposite action of elbow flexion and is performed by other muscles, primarily the triceps brachii. Since the biceps brachii does not extend the elbow, this action is indeed not associated with it, making it the correct answer in this context. Understanding the specific roles of muscles like the biceps brachii helps to clarify their functions in movement and anatomy.