Brachialis muscle

Last revised by Liz Silverstone on 13 Nov 2023

The brachialis muscle is one of the three muscles of the anterior compartment of the upper arm. Unlike biceps brachii (which is also a supinator) it acts only to flex the elbow. Isolated brachialis injuries are rare.


Brachialis has a large superficial head and a smaller deep head.

The superficial head origin is the anterolateral mid humeral shaft and lateral intermuscular septum. Its thick round tendon inserts into the distal portion of the ulnar tuberosity.

The deep head origin is the anterior distal humeral shaft and medial intermuscular septum and its muscle belly lies posterolateral to the superficial head. The distal aponeurosis narrows, merges with the superficial tendon and inserts onto the proximal ulnar tuberosity as well as the coronoid process.

Innervation is from the musculocutaneous nerve and radial nerve (proprioceptive branch).

Brachialis is the most powerful flexor of the elbow and is most effective at 90 degrees of flexion. It is an important elbow stabilizer.

Variant anatomy

Although rare, supernumerary heads of brachialis have been reported and may cause entrapment of the median nerve and/or brachial artery 3.

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