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Brachialis By Christy Cael essential skills | FUNCTIONAL ANATOMY The brachialis muscle is located in the anterior and distal arm just above the crease of the elbow. It is a short, thick muscle that lies beneath the thinner, smaller, and more proximal biceps brachii. There are two distinct heads of the brachialis—one larger and more superficial and a second that is smaller and deeper. The fibers of the smaller, deeper head run at a more oblique angle and attach at the coronoid process of the ulna rather than the tuberosity. This offers better mechanical advantage for initiating elbow flexion from a position of full extension, while the larger, superficial head powers the elbow through flexion. The brachialis is strongly anchored to a broad section of the anterior humerus, specifically the distal half of the anterior surface. This feature allows it to generate large amounts of force without being damaged. It is relatively thick with a high degree of muscle fiber interaction compared to other elbow flexors, making it the prime mover for this action. The brachialis works primarily with the biceps brachii and the brachioradialis to flex the elbow. It differs from the biceps brachii in that it attaches to the ulna rather than the radius; thus, it cannot rotate the forearm. The brachialis is unique in that it is a pure elbow flexor and maintains its leverage regardless of forearm position. Both the biceps brachii and the brachioradialis have varying strength depending on the rotational position of the forearm. Powerful movements like lifting, pulling, and performing chin-ups rely on the brachialis. This muscle is particularly important when the forearm is pronated (palm down), as both the biceps brachii 66 m a s s a g e & b o d y wo r k m a rc h /a p r i l 2 0 2 2 BRACHIALIS ATTACHMENTS O: Distal one-half of anterior surface of the humerus I: Tuberosity and coronoid process of the ulna ACTIONS • Flexes the elbow INNERVATION • Musculocutaneous and radial nerves • C5–C6 Brachialis