Brachialis Muscle Anatomy

The brachialis muscle is a flattened fusiform muscle that lies posterior (deep) to the biceps. Its distal attachment covers the anterior part of the elbow joint.

Of the four major arm muscles, three flexors (biceps brachii, brachialis, and coracobrachialis) are in the anterior (flexor) compartment, supplied by the musculocutaneous nerve, and one extensor (triceps brachii) is in the posterior compartment, supplied by the radial nerve.

Brachialis Muscle Anatomy

Origin

The Brachialis muscle originates from the distal half of anterior surface of humerus.

Insertion

It inserts on the coronoid process and tuberosity of ulna.

See Also: Elbow Anatomy

Innervation

It’s innervated mainly by the musculocutaneous nerve (C5,C6), some of the lateral part of the brachialis is innervated by a branch of the radial nerve.

Blood Supply

Its blood supply comes from muscular branches of brachial artery and recurrent radial artery.

Action & Function

The brachialis muscle is the main flexor of the forearm. It is the only pure flexor, producing the greatest amount of flexion force. Unlike the biceps, the brachialis flexes the forearm in all positions, being unaffected by pronation or supination. It acts during both slow and quick movements and in the presence or absence of resistance.

When the forearm is extended slowly, the brachialis steadies the movement by slowly relaxing, that is, eccentric contraction (e.g., you use it to pick up and put down a teacup carefully). The brachialis always contracts when the elbow is flexed, and it is primarily responsible for sustaining the flexed position. Because of its important and almost constant role, it is regarded as the workhorse of the elbow flexors.

Clinically

The brachialis muscle typically gets split during anterior and anterolateral surgical approaches to the humerus.

Brachialis tendon may be transferred to reconstruct the flexor digitorum profundus and the flexor pollicis longus after brachial plexus injuries.

Tendinopathy of the brachialis muscle at its insertion is a rare event. Generally, the symptom is a pain in the antecubital area, and conservative therapy (steroid injection) is the recommended approach to management.

To test the brachialis muscle, the forearm is semi-pronated and flexed against resistance. If acting normally, the contracted muscle can be seen and palpated.

References & More

1. Clinically Oriented Anatomy – 8th Edition
2. Plantz MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Brachialis Muscle. [Updated 2023 Feb 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551630/
3. McLoughlin E, Iqbal A, Shamji R, James SL, Botchu R. Brachialis tendinopathy: a rare cause of antecubital pain and ultrasound-guided injection technique. J Ultrasound. 2021 Sep;24(3):355-358. [PubMed]