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The supinator muscle is a broad muscle located in the posterior compartment of the forearm, responsible for supinating the forearm. Supination is a unique movement that allows the human body to rotate the hand, wrist, and forearm by almost 180 degrees, enabling the palm to face either up or down. The supinator muscle works in conjunction with the biceps, except when the elbow joint is extended, and plays a crucial role in forearm supination. This muscle consists of two layers of fibres that originate from the ulna and humerus, contributing to the complex mechanics of the human forearm.
| Characteristics | Values |
|---|---|
| Name | Supinator muscle |
| Location | Posterior compartment of the forearm |
| Shape | Broad, flat, fusiform |
| Consists of | Two layers of fibres |
| Innervation | Posterior interosseous nerve, C6, C7 |
| Function | Supinates the forearm |
| Works with | Biceps Brachii |
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What You'll Learn
- The supinator muscle is located in the posterior compartment of the forearm
- The supinator muscle consists of two layers of fibres
- Supination and pronation are unique movements only possible in the forearms and hands
- The supinator muscle works with the biceps brachii for powerful supination
- Supination strength decreases by 64% if the supinator is disabled
The supinator muscle is located in the posterior compartment of the forearm
The supinator muscle is a broad muscle located in the posterior compartment of the forearm. It is a two-plane muscle, with the deeper plane of muscle fibres encircled by the superficial plane. The supinator curves around the upper third of the radius, which is one of the two large bones in the forearm. The muscle fibres originate from the supinator crest of the ulna, the lateral epicondyle of the humerus, the radial collateral ligament, and the annular radial ligament.
The supinator muscle is responsible for supinating the forearm, which involves rotating the palm of the hand upward or anteriorly. This movement is possible due to the supinator muscle pulling on the radius bone, allowing it to rotate at the elbow and wrist joints. The supinator works together with the biceps brachii muscle to achieve powerful supination. However, the biceps brachii cannot supinate when the elbow is fully extended, whereas the supinator can perform this action in all positions of the elbow.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the muscle. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle, which can result in entrapment and potential paralysis of the muscles it serves. This condition is known as supinator entrapment syndrome and can be caused by repetitive supination and pronation movements.
The ability to supinate and pronate the forearm provides enormous mechanical advantage and enhances functionality. It allows for movements such as turning a screwdriver or a key, which require positioning the hand in space for grip and hand movement.
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The supinator muscle consists of two layers of fibres
The supinator muscle is a broad muscle in the superior and posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres, or planes, also known as the superficial and deep layers. The two layers of fibres originate from the supinator crest of the ulna, the lateral epicondyle of the humerus, the radial collateral ligament, and the annular radial ligament. The superficial layer of fibres has a tendinous origin and surrounds the upper part of the radius. The deeper layer of fibres encircles the neck of the radius above the radial tuberosity.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the supinator muscle. The radial nerve divides into deep and superficial branches just proximal to the supinator muscle. This can lead to entrapment and compression of the deep branch, potentially resulting in selective paralysis of the muscles served by this nerve. This nerve syndrome is known as supinator entrapment syndrome and can be caused by compression by various soft-tissue masses surrounding the nerve and stress caused by repetitive supination and pronation.
The supinator muscle rotates the radius laterally at the proximal radioulnar joint, bringing the hand into the supine position (facing anteriorly, palm up). This movement is known as forearm supination. The supinator muscle is the prime supinator of the forearm and always acts together with the biceps muscle. However, the biceps muscle cannot act as a supinator when the elbow joint is extended. When a quick, strong, or forceful supination movement is required, or when the movement happens against resistance, the supinator muscle is assisted by the biceps brachii muscle.
Supination moves the hand, wrist, and forearm almost 180 degrees so that the palm faces anteriorly or superiorly, depending on the position of the arm. This is in contrast to pronation, which involves placing the palms into the prone (face-down) position. The pronator teres and pronator quadratus muscles work together to achieve pronation by pulling on the radius bone of the forearm.
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Supination and pronation are unique movements only possible in the forearms and hands
The human body is capable of a wide range of movements, but supination and pronation are unique to the forearms and hands. These movements allow the palm to be flipped either face up or face down. The muscles, bones, and joints of the human forearm are specifically arranged to permit these unique and important rotations of the hands. The ability to supinate and pronate gives us enormous mechanical advantage and enhanced functionality.
The anatomical position is when the arms are fully extended to the sides of the trunk with the palms facing forward. In this position, the arms are already supinated. Pronation involves moving the hand so that the palms face posteriorly, or face down. This is achieved by the pronator teres and pronator quadratus muscles, which work together to pull on the radius bone of the forearm. The radius rotates at the elbow and wrist joints around the ulna, the other forearm bone.
Supination is the opposite movement of pronation. It involves turning the palms anteriorly or superiorly to the supine (face-up) position. The supinator muscle of the forearm and the biceps brachii of the upper arm 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 located in the posterior compartment of the forearm and is the prime supinator of the forearm. It curves around the upper third of the radius and consists of two layers of fibres. 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.
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The supinator muscle works with the biceps brachii for powerful supination
The supinator muscle is a broad muscle located in the posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres. The supinator muscle's main function is to supinate the forearm. This movement involves rotating the hand, wrist, and forearm almost 180 degrees so that the palm faces upward or anteriorly.
The biceps brachii is a muscle in the upper arm that also plays a role in supination. It acts as a powerful supinator when the forearm is in a pronated position. The biceps brachii is attached to the ulna, which allows it to provide a strong supination moment.
When powerful supination is required, the supinator muscle works together with the biceps brachii. The biceps brachii is unable to supinate when the elbow is fully extended, so the supinator muscle takes over as the primary supinator in this position. The supinator muscle is always active during forearm supination, even when the biceps brachii is involved.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the muscle. This nerve passes through the belly of the supinator in most cases. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle, which can lead to entrapment and potential paralysis of the muscles it serves.
The combination of the supinator muscle and the biceps brachii allows for effective and powerful supination of the forearm. This movement is important for various functional activities, such as turning a screwdriver or a key.
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Supination strength decreases by 64% if the supinator is disabled
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres. Its function is to supinate the forearm. The supinator works with the biceps brachii muscle to achieve powerful supination. However, the biceps are unable to supinate when the elbow is extended.
Supinator entrapment syndrome is a nerve syndrome that can be caused by compression by various soft-tissue masses surrounding the nerve and stress caused by repetitive supination and pronation. This can lead to selective paralysis of the muscles served by the nerve, including the extensor muscles and the abductor pollicis longus.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the supinator muscle. Its nerve roots are primarily from C6, with some C5 involvement, and possible additional C7 innervation.
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Frequently asked questions
The supinator muscle is the prime muscle responsible for supinating the forearm.
Supination is a unique movement that occurs in the forearms and hands, allowing the human body to flip the palm either face up or face down.
The supinator muscle's main function is to supinate the forearm. It works with the biceps brachii to achieve powerful supination.
The supinator muscle is located in the posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the muscle.
