Brachialis
Musculus brachialis
Also known as: workhorse of the elbow
A broad muscle deep to biceps from the anterior distal humerus to the coronoid process of the ulna. It is the main flexor of the elbow in every forearm position.
Overview
Brachialis arises from the distal half of the anterior surface of the humerus and the intermuscular septa. It crosses the front of the elbow joint and inserts on the coronoid process and tuberosity of the ulna. Because it attaches to the ulna, which cannot rotate, rotating the forearm does not change its action. It flexes the elbow equally well in pronation, supination and mid-position, at any speed and against any load, which earns it the title "workhorse" of elbow flexion. It is the main flexor during slow, unresisted flexion and in eccentric lowering.
Most of the muscle is supplied by the musculocutaneous nerve. A small lateral part receives a twig from the radial nerve, a remnant of its development. Brachialis forms the floor of the cubital fossa and protects the elbow joint anteriorly.
Anatomy
- Origin
Distal half of the anterior surface of the humerus and the medial and lateral intermuscular septa.
- Insertion
Coronoid process and tuberosity of the ulna.
- Action
Flexion of the forearm at the elbow.
- Innervation
Musculocutaneous nerve; small lateral part supplied by the radial nerve.
- Nerve roots
C5–C6 (musculocutaneous); C7 (radial contribution)
- Arterial supply
Muscular branches of the brachial artery; radial recurrent artery.
- Relations
Deep to biceps, with the musculocutaneous nerve between them. Forms the floor of the cubital fossa. The radial nerve lies between it and brachioradialis laterally.
Function
- Flexes the elbow in all forearm positions
Clinical significance
Myositis ossificans
After elbow dislocations or supracondylar fractures, haematoma within brachialis can ossify. This causes a painful mass and limits elbow flexion. Aggressive massage early after injury increases the risk.
Test yourself
Which muscle is the "workhorse" elbow flexor, acting in every forearm position?
- Biceps brachii
- Brachialis
- Brachioradialis
- Pronator teres
Answer: Brachialis
Brachialis inserts on the ulna (coronoid process and tuberosity), so forearm rotation does not affect it. It flexes the elbow in pronation, supination and mid-position.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.