Brachialis · What Is It, Location, Function, and More

The brachialis muscle is a deep muscle located in the upper limb that is mainly responsible for elbow flexion (i.e., the movement that allows the forearm to move closer to the upper body).  

In most people, the brachialis muscle is innervated medially by the musculocutaneous nerve (C5-C6) and laterally by the radial nerve (C7). Blood to the brachialis is supplied primarily by the brachial artery and branches of the radial recurrent artery. Occasionally, the ulnar collateral arteries may also provide blood to this muscle. 

The brachialis muscle is one of the three muscles located in the anterior compartment of the upper arm, alongside the biceps brachii muscle—or simply biceps—and the coracobrachialis. The muscle fibers of the brachialis muscle join to form the brachialis tendon, which connects the brachialis muscle to the humerus at one end and the ulna at the other. Proximally, the brachialis tendon originates mid-shaft through the humerus. It then extends distally and crosses the elbow joint to attach to the coronoid process and the tuberosity of the ulna. 

The main function of the brachialis muscle is flexion of the forearm at the elbow joint. Unlike the biceps, which also helps with forearm supination and shoulder flexion, the brachialis is a pure elbow flexor. This is because the brachialis inserts into the ulna, a bone that stays fixed during supination and pronation. Since its position and function don’t change with forearm rotation, the brachialis can consistently generate force regardless of the forearm position. In fact, it becomes the main elbow flexor when the forearm is pronated and at 90°, a position where the biceps loses mechanical advantage and contributes less to the movement. 

Functionally, the brachialis is most active in pulling movements like rows, hammer curls, or when picking up heavy objects with palms facing each other or down.