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Portrait of Brachialis

Anatomy · Muscles

Brachialis

The 'workhorse' of elbow flexion

Upper limb · arm, anterior compartment

Brachialis is a broad muscle lying deep to the biceps on the lower front of the humerus. It arises from the anterior humerus and inserts on the ulna, so it flexes the elbow whatever position the forearm is in. It is supplied mainly by the musculocutaneous nerve.

How to spot them

  • ▸Sits underneath the biceps, on the lower half of the front of the humerus
  • ▸Attaches to the ulna rather than the radius, so it cannot turn the forearm
  • ▸Its outer edge peeks out beside the biceps on the lateral arm
  • ▸Often called the workhorse of elbow flexion

What to know

A deep muscle of the front of the arm that lies directly on the lower humerus and elbow joint capsule

Brachialis.

The one muscle that flexes the elbow with equal strength whether the palm faces up, down or sideways

Brachialis — it inserts on the ulna, which does not rotate.

Its tendon attaches to the coronoid process and tuberosity of the ulna

Brachialis.

The muscle beneath the biceps: its origin is the front of the lower half of the humerus

Brachialis.

A flexor of the elbow with a small strip on its outer side supplied by the radial nerve

Brachialis — dual nerve supply: musculocutaneous, with a small lateral part from the radial nerve.

Sometimes called the 'workhorse' of elbow flexion

Brachialis — the strongest single elbow flexor.

Key ideas

  • Because it inserts on the ulna, which does not rotate, brachialis flexes the elbow without regard to pronation or supination.
  • It lies beneath the biceps and helps to protect the front of the elbow joint capsule.

Quick-fire facts

  • •Origin: distal half of the anterior surface of the humerus and the intermuscular septa.
  • •Insertion: coronoid process and tuberosity of the ulna.
  • •Nerve supply: musculocutaneous nerve (C5–C6), with a small lateral part sometimes supplied by the radial nerve.
  • •Action: flexes the elbow; the main flexor of the joint.
  • •It lies deep to biceps brachii, which is why the biceps takes most of the credit.
  • •Its dual innervation is unusual in the arm; most muscles have a single nerve.
  • •Brachialis and biceps both attach to the forearm bone below the elbow, but on different bones: ulna and radius respectively.

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