What role does the biceps brachii muscle play in arm movement?

The biceps brachii muscle primarily functions as a flexor of the elbow joint. When it contracts, it pulls the forearm towards the shoulder, which effectively decreases the angle at the elbow, resulting in flexion of the arm. In addition to this primary function, the biceps brachii also plays a role in supination of the forearm, which is the action of turning the palm upwards. Its anatomical location and muscle fiber orientation make it especially effective for these movements, distinguishing it from other muscles involved in arm motion. Therefore, the correct identification of the biceps brachii's role as a flexor accurately reflects its contribution to arm movement during activities that require bending at the elbow.