Supinator
The muscle that wraps around the top of the radius to turn your palm up — with a nerve running through it.
- Type
- Muscle
- Region
- Forearm
- Standard name
- m. supinator
- Origin
- Lateral epicondyle of the humerus, the radial collateral and annular ligaments, and the supinator crest of the ulna
- Insertion
- Upper third of the radius, wrapping its lateral and anterior surfaces
- Actions
- forearm supination
- Verify
- TA2 2512 TA98 A04.6.02.048
What it is
A broad muscle wrapping around the upper third of the radius like a sleeve, arising from both the humerus and the ulna. Its fibres spiral, which is what allows it to unwind the radius.
The deep branch of the radial nerve passes through it, entering between its two layers and emerging on the back of the forearm as the posterior interosseous nerve. This passage is the reason the muscle appears in clinical discussions of forearm nerve entrapment.
What it does
Supinates the forearm — turns the palm upward — and that is its only action.
It works with biceps brachii, and the division of labour between them is worth knowing: this muscle handles unresisted supination at any elbow angle; biceps is recruited when the movement is resisted or fast, and is at its strongest with the elbow bent.
What loads it
Resisted supination, particularly with the elbow straight, which reduces what biceps can contribute.
What is commonly got wrong about it
That biceps is the supinator. Biceps is the stronger one, and this is the one that does the everyday work.
That supination is a wrist movement. It happens between radius and ulna.
"Tennis elbow" and this muscle. Lateral elbow pain is usually attributed to the common extensor origin nearby. Radial nerve entrapment at this muscle is a separate and much less common possibility, and telling them apart requires examination.