The brachialis is the deepest anterior elbow flexor, lying directly over the anterior humerus under the biceps brachii and inserting directly onto the ulna rather than the radius. Because the ulna cannot rotate, the brachialis generates pure elbow flexion torque independent of forearm position, making it the true workhorse of elbow flexion in every grip orientation from supinated curls to hammer curls to pronated reverse curls.
| Origin | Lower half of the anterior surface of the humerus and the adjacent intermuscular septa |
|---|---|
| Insertion | Tuberosity of the ulna and the coronoid process |
| Nerve Supply | Musculocutaneous nerve (C5, C6) for the main portion; Radial nerve (C7) for a small lateral strip |
| Blood Supply | Brachial artery |
| Actions | Flexion of the elbow in all forearm positions regardless of rotation |
|---|
As the only elbow flexor that inserts on the ulna, it is equally effective at all forearm rotation angles. When the biceps is limited by an unfavorable supination angle, the brachialis picks up the load, making it the most consistently active elbow flexor across all functional tasks.
The brachialis maintains meaningful elbow flexion strength even after a complete distal biceps tendon rupture, which is why patients can still bring a cup to their mouth despite the dramatic visible deformity. A partial brachialis strain produces anterior elbow pain that is reproduced during hammer curls or pronated grip pulling rather than supinated curls, which is the clinical key to distinguishing it from biceps pathology.
The brachialis is palpable deep to the biceps in the distal anterior upper arm, most accessible just medial to the biceps tendon in the antecubital region during resisted elbow flexion with the forearm in neutral rotation.
Partial tearing of the brachialis from a sudden eccentric overload during neutral or pronated grip pulling, producing anterior elbow pain that is deeper and more diffuse than a biceps strain and reproduced by resisted elbow flexion in those grip positions.
Calcium deposition within the brachialis following direct contusion or repeated trauma to the anterior elbow, producing a firm bony mass with progressive elbow flexion restriction that requires imaging to distinguish from a tumour.
