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The supinator muscle is a broad muscle in the posterior compartment of the forearm. It is responsible for supinating the forearm, or twisting the forearm into the palm-up position. The supinator muscle works together with the biceps to achieve this movement, except when the elbow joint is extended. The supinator muscle is innervated by the deep branch of the radial nerve, which passes through its two heads. This muscle is essential for allowing the human body to rotate the palm up and down, providing about half the power of the biceps muscle for supination.
| Characteristics | Values |
|---|---|
| Location | Just below the elbow |
| Function | Supination of the forearm |
| Composition | Two planes of fibres: superficial and deep |
| Innervation | Radial nerve (deep branch) |
| Blood Supply | Ulnar artery |
| Attachments | Originates from the lateral epicondyle of the humerus and the posterior surface of the ulna |
| Insertions | Inserts onto the posterior surface of the radius |
| Related Muscles | Biceps Brachii, Brachialis, Brachioradialis |
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What You'll Learn
The supinator muscle is located just below the elbow
The supinator muscle is innervated by the deep branch of the radial nerve. The deep branch then becomes the posterior interosseous nerve upon exiting the supinator muscle. Its nerve roots are primarily from C6, with some C5 involvement. The median nerve innervates the muscle of the anterior compartment of the forearm. It has two heads, an ulnar and a humeral. The larger and more superficial humeral head arises from the medial supracondylar ridge. The ulnar head is thin and arises from the medial surface of the coronoid process. The median nerve passes through the two heads to reach the forearm.
The supinator muscle is the most active muscle in forearm supination during unresisted supination, while the biceps become increasingly active with heavy loading. Supination strength decreases by 64% if the supinator is disabled by, for example, injury. The supinator muscle is also important as a location where the radial nerve can be entrapped. The radial nerve divides just prior to the supinator, with the branch supplying muscles travelling through the supinator muscle between its two heads.
The supinator muscle works with the biceps brachii to supinate the forearm by pulling on the radius. These muscles rotate the radius in the opposite direction of the pronator muscles, moving the distal end of the radius back to its position on the lateral side of the wrist. The supinator muscle is essential for human functionality, allowing us to perform everyday tasks such as turning a screwdriver or turning a key.
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The biceps brachii acts as a supinator when the elbow is flexed
The biceps brachii is one of three muscles that flex the elbow. It also functions as a supinator of the forearm, turning the palm upwards. This action is aided by the supinator muscle, which is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. The supinator muscle consists of two planes of fibres, between which passes the deep branch of the radial nerve.
The biceps brachii is a powerful supinator of the forearm due to the distal attachment of the muscle at the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps effectively pull the radius back into its neutral supinated position in concert with the supinator muscle. The biceps work across three joints, with the most important function being to supinate the forearm and flex the elbow. The long head of the biceps also prevents the upward displacement of the head of the humerus.
The biceps brachii is involved in tasks such as lifting, sports involving throwing and racket use, and gesturing. As a result, biceps tendinopathy is a common condition seen in the muscle. Most occur as a result of physical trauma or repetitive activity. Tears of the biceps brachii may occur during athletic activities, and avulsion injuries of the distal biceps tendon are frequently occupational in nature and sustained during forceful, eccentric contraction of the biceps muscle while lifting.
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The supinator muscle consists of two planes of fibres
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It is responsible for supinating the forearm, which is the action of turning the hand so that the palm faces upwards. This muscle works in tandem with the biceps to achieve this movement.
From these origins, the supinator muscle wraps, or spirals, around the proximal third of the radius, inserting into the upper third of its lateral, posterior, and anterior surfaces. This unique anatomy allows the supinator muscle to rotate the radius laterally, producing the movement known as forearm supination. The supinator's famous antagonist is the pronator quadratus muscle, which performs the opposite movement of pronation by rotating the radius medially.
The supinator muscle is innervated by the deep branch of the radial nerve, which passes between the two planes of fibres. This nerve becomes the posterior interosseous nerve upon exiting the supinator muscle, with nerve roots primarily from C6 and some involvement from C5 and potentially C7. The two layers of the supinator muscle are supplied by two different sources: the superficial layer receives blood from the radial artery, while the deep layer is supplied by the ulnar artery.
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The supinator muscle is innervated by the radial nerve
The supinator muscle is a spiral muscle that rotates the radius laterally to accomplish forearm supination. It is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm. The supinator muscle always acts together with the biceps, except when the elbow joint is extended. It is the most active muscle in forearm supination during unresisted supination, while the biceps become increasingly active with heavy loading.
The supinator muscle is innervated by the deep branch of the radial nerve. The radial nerve divides into deep and superficial sensory branches just proximal to the supinator muscle. This arrangement can lead to entrapment and compression of the deep part, potentially resulting in selective paralysis of the muscles served by this nerve. This nerve syndrome is known as supinator entrapment syndrome, which can be caused by compression by various soft-tissue masses surrounding the nerve and stress caused by repetitive supination and pronation.
The deep branch of the radial nerve passes through the belly of the supinator in 70% of cases and via the arcade of Frohse in the remaining cases. The nerve roots are primarily from C6, with some C5 involvement and possible additional C7 innervation. The radial nerve arises from the lateral supracondylar ridge and lateral intermuscular septum of the arm.
The supinator muscle is also assisted by the biceps brachii muscle for quick, strong, and forceful supination movements, or when the movement happens against resistance. The biceps brachii cannot act as a supinator when the forearm is fully extended. Therefore, the most powerful supination occurs when the elbow joint is flexed to 90 degrees.
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The biceps is the main supinator of the forearm
The act of supinating the forearm involves twisting it into the palm-up position. The supinator muscle of the forearm and the biceps brachii of the upper arm are the muscles responsible for supinating the forearm. The biceps is the main supinator of the forearm, with the supinator muscle providing about half of the power of the biceps muscle for supination. The biceps brachii acts primarily as an elbow flexor and secondarily as a supinator. It is able to supinate when the elbow is flexed. When the elbow is fully extended, the supinator muscle performs the action. The supinator muscle is located just below the elbow and is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm. The supinator always acts together with the biceps, except when the elbow joint is extended. The supinator is the most active muscle in forearm supination during unresisted supination, while the biceps become increasingly active with heavy loading. Supination strength decreases by 64% if the supinator is disabled, for example, by injury.
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Frequently asked questions
Supination is the act of twisting the forearm into the palm-up position.
The supinator is a muscle within the deep compartment of the posterior forearm. It forms the floor of the cubital fossa and has two heads.
The supinator muscle supinates the forearm, bringing the hand into the supinated position. It works with the biceps brachii to achieve this.
The biceps is the main supinator of the forearm, helping us rotate the palm up and down. It acts together with the supinator, except when the elbow joint is extended.
The radial nerve is involved in supination. It divides into deep and sensory superficial branches just proximal to the supinator muscle.
