What is the action of the biceps brachii?

The biceps brachii is primarily responsible for elbow flexion, which is the action of bending the elbow. This muscle is located in the upper arm and has two heads: the long head and the short head. When the biceps brachii contracts, it brings the forearm closer to the shoulder, effectively bending the elbow joint.

Additionally, the biceps brachii plays a role in shoulder stabilization and assists in supination of the forearm, which is the action of turning the palm upward. However, its main function remains elbow flexion, which is why the choice referring to this action is considered the correct answer. Understanding this muscle's primary action is essential in fields such as kinesiology and physical therapy, where knowledge of muscle movements is crucial for assessing and treating functional movement patterns.