Anatomy

Brachialis

March/April 2022

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 muscle on an arm.
The brachialis muscle. Image copyright 2010 Wolters Kluwer Health, Lippincott Williams & Wilkins.

Brachialis

Attachments

  • Origin: Distal one-half of anterior surface of the humerus
  • Insertion: Tuberosity and coronoid process of the ulna

Actions: Flexes the elbow.

Innervation

  • Musculocutaneous and radial nerves
  • C5-C6

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 and the brachioradialis lose their mechanical advantage in this position. Both the brachialis and the biceps brachii are rapid flexors; that is, their position on the arm generates quick movement through a large range of motion. The forces produced by the brachialis and the biceps brachii are distributed between the ulna and the radius, maximizing joint function and minimizing injury.

A Deeper Diver—Palpating the Brachialis

Positioning: client supine with forearm pronated.

an MT palpating the brachialias with client supine with forearm pronated.
Image courtesy Christy Cael.

  1. Passively flex the elbow to slack tissue.
  2. On the anterior upper arm, find the medial and lateral borders of the elbow flexors in a pincer grasp.
  3. Gently slide the fingers distally toward the elbow crease, stopping a few inches above.
  4. Have the client gently resist elbow flexion to ensure proper location.

Passive Stretching of the Brachialis

Positioning: client supine with the elbow flexed and forearm supinated.

MT performing a passive stretch with a female client supine with the elbow flexed and forearm supinated.
Image courtesy Christy Cael.

  1. Stand at the client's side and support the wrist and elbow.
  2. As the client remains relaxed, straighten the elbow into full extension.
  3. The end-feel will be springy or bouncy if limited by muscle tension in the elbow flexors and firm or hard if limited by the humeroulnar joint structures.
  4. Use the thumb of your proximal hand to locate and assess tension and soft-tissue qualities of the brachialis muscle belly and tendon throughout the range of motion.
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