Final answer:
The biceps brachii, along with the brachialis and brachioradialis, are muscles that flex the forearm. When the biceps brachii contracts, it pulls the forearm upward toward the humerus through the action of elbow flexion.
Step-by-step explanation:
The biceps brachii, along with the brachialis and brachioradialis, are muscles that flex the forearm. The biceps brachii is a two-headed muscle that crosses the shoulder and elbow joints to flex the forearm while also helping to supinate it and flex the arm at the shoulder. When the biceps brachii contracts, it pulls the forearm upward toward the humerus through the action of elbow flexion.