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The forearm is the section of the upper limb from the elbow to the wrist, and its bony structure is formed by the radius and ulna. There are twenty muscles in the forearm, divided into two muscular compartments: an anterior (flexor) and posterior (extensor) compartment. These muscles are essential to the fine motor actions of the upper limb, allowing for complex movements of the arm, wrist, and fingers. The forearm muscles can be divided into four groups: forearm flexors, forearm extensors, forearm pronators, and forearm supinators. The flexor carpi radialis helps move your arm away from your body, while the palmaris longus helps flex the wrist. The flexor digitorum superficialis is the only muscle in the intermediate layer and helps you bend your fingers and move your wrist. The supinator muscle allows you to supinate your forearm, which means to turn it so that your palm faces up. The biceps brachii, brachialis, and brachioradialis are forearm flexors, while the triceps brachii and anconeus are forearm extensors.
| Characteristics | Values |
|---|---|
| Number of muscles in the forearm | 20 |
| Number of muscle compartments | 2 |
| Types of muscle compartments | Anterior (flexor) and posterior (extensor) |
| Types of muscles | Intrinsic and extrinsic |
| Function of intrinsic muscles | Move the forearm by pronating and supinating the radius and ulna |
| Function of extrinsic muscles | Flex and extend the digits of the hand |
| Forearm flexors | Biceps brachii, brachialis, and brachioradialis |
| Forearm extensors | Triceps brachii and anconeus |
| Forearm pronators | Pronator teres and pronator quadratus |
| Forearm supinators | Supinator muscle |
| Blood supply to forearm and hand | Radial and ulnar arteries |
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What You'll Learn
Forearm flexors
The forearm is the section of the upper limb from the elbow to the wrist, with a bony structure formed by the radius and ulna. The muscles that move the forearm can be divided into four groups: forearm flexors, forearm extensors, forearm pronators, and forearm supinators. The flexors and extensors act on the elbow joint, while the pronators and supinators act on the radioulnar joints.
The forearm flexors include the biceps brachii, brachialis, and brachioradialis. The biceps brachii is a two-headed muscle located on the anterior upper arm. It flexes the elbow and supinates the forearm. The brachialis lies directly beneath the biceps brachii and helps flex the elbow. The brachioradialis is located on the lateral forearm and flexes the elbow, causing both pronation and supination of the forearm.
The superficial anterior forearm muscles are a group of five muscles located in the anterior (flexor) compartment of the forearm. These muscles include the pronator teres, flexor carpi radialis, flexor carpi ulnaris, palmaris longus, and flexor digitorum superficialis. The majority of muscles from this group are innervated by the median nerve, except for the flexor carpi ulnaris and medial half of flexor digitorum profundus, which are innervated by the ulnar nerve. All of the muscles in this compartment work together to produce movements of the hand and digits. Specifically, they are in charge of flexion, adduction, and abduction of the hand at the wrist joint, as well as flexion of the fingers at the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints.
The flexor carpi radialis is a muscle situated medially to the pronator teres muscle. It originates from the medial epicondyle of the humerus and extends to the midpoint of the forearm, where it turns into a long tendon. The tendon passes beneath the flexor retinaculum and attaches to the bases of the metacarpal bones 2-3. The flexor carpi radialis produces movements of the hand at the wrist joint, including wrist flexion and wrist abduction.
The flexor carpi ulnaris is the most medial muscle of this group. It originates from two heads; humeral and ulnar. The humeral head arises from the medial epicondyle of the humerus, while the ulnar head arises from the olecranon and proximal two-thirds of the posterior surface of the ulna. The flexor carpi ulnaris is the only muscle in this group that receives its innervation via the ulnar nerve. It contributes to the flexion of the hand at the wrist joint.
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Forearm extensors
The forearm is the section of the upper limb that extends from the elbow to the wrist. The forearm muscles are divided into two compartments: the anterior flexor compartment and the posterior extensor compartment. The muscles in the posterior compartment of the forearm are commonly known as the extensor muscles. These muscles produce extension at the wrist and fingers.
The forearm extensors include the triceps brachii and anconeus. The triceps brachii is a three-headed muscle located at the back of the upper arm. It extends the forearm at the elbow joint and the arm at the shoulder joint. The anconeus is a small triangular muscle at the elbow joint that also extends the forearm.
The superficial posterior forearm muscles are a group of six muscles situated in the superficial layer of the posterior compartment of the forearm. These muscles include the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi. The extensor digitorum is the main extensor of the fingers. The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm and produce abduction as well as extension at the wrist. The extensor carpi ulnaris is located on the medial aspect of the posterior forearm, which allows it to produce adduction as well as extension at the wrist.
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Forearm pronators
The forearm is the section of the upper limb between the elbow and the wrist. The muscles that move the forearm can be divided into four groups: forearm flexors, forearm extensors, forearm pronators, and forearm supinators. The forearm pronators are the muscles that pronate the forearm, turning the hand so that the palm faces the ground or posteriorly.
The pronator teres and pronator quadratus are forearm pronator muscles. The pronator teres is a long, round muscle located on the anterior aspect of the forearm. It has two points of origin: the humeral head and the ulnar head. The humeral head is larger and more superficial, arising from the medial supracondylar ridge of the humerus, while the ulnar head is deeper and joins it at an acute angle. The two heads eventually fuse into a single muscle belly that inserts via a flat tendon onto the lateral surface of the radius. The pronator teres is innervated by the median nerve and nerve roots C6 and C7. It acts synergistically with the pronator quadratus.
The pronator quadratus originates on the distal shaft of the ulna and inserts onto the distal part of the radius. The supinator muscle, on the other hand, supinates the forearm. It originates from the lateral epicondyle of the humerus and inserts on the lateral surface of the proximal one-third of the radius.
The brachioradialis muscle is also involved in pronation and supination of the forearm, in addition to flexing the elbow. It originates on the lateral border of the distal end of the humerus and inserts on the radius, superior to the styloid process.
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Forearm supinators
The muscles that move the forearm can be divided into four groups: forearm flexors, forearm extensors, forearm pronators, and forearm supinators. The forearm supinator is a broad muscle in the posterior compartment of the forearm, which curves around the upper third of the radius. The supinator muscle supinates the forearm, working with the biceps brachii to produce powerful supination. The biceps brachii, however, cannot act as a supinator when the forearm is fully extended.
The supinator muscle has a broad origin from the ulna and humerus. The two layers of fibres originate in common 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 rotates the radius laterally at the proximal radioulnar joint, bringing the hand into the supine position.
The supinator is innervated by the posterior interosseous nerve (C7, C8), a branch of the radial nerve. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle, which can lead to entrapment and compression of the deep branch and potentially result 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.
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Flexion and extension of the wrist
The forearm is the section of the upper limb from the elbow to the wrist, with a bony structure formed by the radius and ulna. The forearm muscles are divided into two compartments: the anterior flexor compartment and the posterior extensor compartment. These compartments contain twenty muscles that act on the elbow and wrist joints, allowing for complex movements of the arm, wrist, and fingers.
Flexion is the motion of bending the wrist towards the palm. The muscles involved in this movement include the flexor carpi ulnaris, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis. The flexor carpi ulnaris and flexor carpi radialis are the prime movers, while the palmaris longus tightens the skin and fascia in the palm. The flexor digitorum superficialis assists as a finger flexor.
The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can be classified as a superficial muscle, but it usually lies between the deep and superficial muscle layers. This muscle splits into four tendons at the wrist, travelling through the carpal tunnel and attaching to the base of the middle phalanx of the four digits. It flexes the metacarpophalangeal joints and proximal interphalangeal joints at the fingers, as well as flexing the wrist.
There are three muscles in the deep anterior forearm: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The flexor digitorum profundus originates from the ulna and associated interosseous membrane. It splits into four tendons, passing through the carpal tunnel and attaching to the distal phalanges of the fingers. This muscle is responsible for flexing the distal interphalangeal joints of the fingers, as well as the metacarpophalangeal joints and the wrist.
Extension is the opposite of flexion, involving the movement of the hand backward so that the palm faces up. Muscles involved in extension include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digitorum. The first two are prime movers, while the extensor carpi ulnaris and extensor digitorum assist in the movement.
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Frequently asked questions
Five muscles specifically move the forearm: the pronator teres, the pronator quadratus, the anconeus, the brachioradialis, and the supinator.
The pronator teres and pronator quadratus rotate the forearm about the elbow joint. The supinator moves the forearm so that the forearm and palms face forward from the body. The anconeus, a small muscle located near the elbow, aids in the extension of the elbow. Flexion at the elbow is carried out by the brachioradialis.
Examples of forearm flexion include lifting a glass of water to your mouth or doing a bicep curl.
The forearm muscles fall into two categories: intrinsic and extrinsic muscles. The intrinsic muscles function to move the forearm by pronating and supinating the radius and ulna. The extrinsic muscles flex and extend the digits of the hand.
Some conditions that can affect the forearm muscles include muscle strain, rhabdomyolysis, and Volkmann's ischemic contracture.
