Which muscle assists the supinator in rotating the forearm?

The biceps brachii (m. biceps brachii) is a powerful forearm supinator when the elbow is flexed, inserting onto the radial tuberosity.

How can you distinguish the radius from the ulna when studying supinator attachments?

Anatomically, the radius is always located laterally in the forearm, while the ulna is medial. The supinator originates partly from the ulnar crest and inserts onto the lateral surface of the radius.

What other muscles share innervation with the supinator via the radial nerve?

The radial nerve also innervates the triceps brachii, anconeus, brachioradialis, extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.

Supinator Muscle: Anatomy, Origin, Insertion & Innervation

Supinator Muscle

m. supinator

For medical students2 min readUpdated 2026-10-10

The supinator muscle (m. supinator) is a deep muscle located in the posterior compartment of the forearm, responsible for supination of the forearm. It covers the lateral aspect of the elbow joint capsule and forms the supinator canal, through which the deep branch of the radial nerve emerges into the posterior forearm.

ActionSupination of the forearm (especially when the elbow is extended)

InnervationDeep branch of the radial nerve (C6–C7)

Blood SupplyRadial recurrent artery and posterior interosseous artery

TopographyDeep layer of the posterior forearm compartment

Location and Structure

The supinator lies in the deep layer of the posterior forearm. Etymologically, its name derives from supinatum (to turn upward) combined with the suffix -or (denoting the agent of an action).

Origin (O): Lateral epicondyle of the humerus (epicondylus lateralis), radial collateral ligament (lig. collaterale radiale), annular ligament of the radius (lig. anulare radii), and the supinator crest of the ulna.
Insertion (I): Proximal (upper) third of the lateral and anterior-lateral surfaces of the radius.

Topography and Relations

The supinator plays a crucial topographic role in the elbow region:

Joint Relation: The muscle directly covers the lateral aspect of the elbow joint capsule, providing structural protection (whereas the medial capsule lacks muscular reinforcement).

What Passes Through the Supinator Canal?

The muscle consists of superficial and deep heads, between which the supinator canal (canalis supinatorius) is formed.

At the level of the lateral epicondyle, the radial nerve divides into its terminal branches. Its deep branch (r. profundus n. radialis) courses laterally and enters this canal. Within the canal, the nerve and the supinator wrap around the neck of the radius before emerging into the posterior forearm compartment to innervate the extensor muscles.

Function, Blood Supply, and Innervation

Action (A): Supinates the forearm (rotates it laterally). This action is most powerful when the elbow joint is extended. Note: The biceps brachii (*m. biceps brachii) is also a major supinator.*
Blood Supply: Branches of the radial recurrent artery (a. recurrens radialis) and the posterior interosseous artery (a. interossea posterior).
Innervation (N): Deep branch of the radial nerve (n. radialis), carrying fibers from spinal cord segments C6–C7.

Clinical Significance

Mononeuropathies: Neurological evaluations of the upper extremity assess motor function, muscle strength, and trophic status of the supinator, along with other radial nerve-innervated muscles such as wrist and finger extensors, brachioradialis, and triceps brachii.
Extrapyramidal Disorders: Lesions of the extrapyramidal system (e.g., extrapyramidal rigidity) cause a uniform increase in muscle tone affecting both pronators and supinators equally.

Frequently asked questions

Which muscle assists the supinator in rotating the forearm?: The biceps brachii (m. biceps brachii) is a powerful forearm supinator when the elbow is flexed, inserting onto the radial tuberosity.
How can you distinguish the radius from the ulna when studying supinator attachments?: Anatomically, the radius is always located laterally in the forearm, while the ulna is medial. The supinator originates partly from the ulnar crest and inserts onto the lateral surface of the radius.
What other muscles share innervation with the supinator via the radial nerve?: The radial nerve also innervates the triceps brachii, anconeus, brachioradialis, extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.

Go deeper

Radial nerve (n. radialis)
Ulna
Radius
Biceps brachii muscle (m. biceps brachii)