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The elbow joint is where the upper arm bone (humerus) meets the forearm bones (radius and ulna). Forearm pronation is produced by the forearm muscles, including pronator teres, pronator quadratus, and flexor carpi radialis. The brachioradialis muscle also pronates the forearm when flexing the elbow. The pronator teres is the hardest-working muscle during elbow flexion with simultaneous hand pronation.
| Characteristics | Values |
|---|---|
| Muscles that pronate the elbow | Pronator teres, pronator quadratus, flexor carpi radialis, and brachioradialis |
| Elbow joint | Where the humerus meets the radius and ulna |
| Elbow flexion | Bending |
| Elbow extension | Straightening |
| Pronation | Turning the forearm inward so the palm faces down |
| Supination | Turning the forearm outward |
| Brachialis function | Most powerful muscle among flexors |
| Brachialis attachment | To the ulna, which cannot rotate, making it the only true flexor of the elbow |
| Brachialis daily use | Picking up shopping bags |
| Brachialis strengthening exercises | Bicep curls using a resistance band |
| Biceps brachii | Powerful supinator when the limb is pronated |
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Pronator teres
The pronator teres is a muscle that is primarily located in the forearm. It is responsible for pronating the forearm, or turning the palm of the hand downwards. This muscle works together with the pronator quadratus to achieve this movement. When the elbow is flexed at a right angle, the pronator teres rotates the hand so that the palm faces inferiorly.
The pronator teres 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 above the medial epicondyle of the humerus. The ulnar head, also known as the ulnar tuberosity, is thinner and arises from the medial side of the coronoid process of the ulna. It joins the humeral head at an acute angle, forming one muscle belly. The ulnar head can vary in composition, ranging from tendinous to muscular, and in some cases, it may be absent.
The median nerve typically enters the forearm by passing between the two heads of the pronator teres. This nerve is responsible for innervating the muscle and is susceptible to compression at this site, leading to a condition known as pronator teres syndrome. This syndrome is characterised by pain, numbness, and possible motor dysfunction in the affected individual.
To target the pronator teres muscle specifically during exercises, it is important to avoid excessive flexion of the elbow. When the elbow is fully flexed, the muscle fibres of the pronator teres shorten, reducing their ability to generate force. Therefore, maintaining an appropriate elbow position is crucial to effectively engage the pronator teres during pronation and supination exercises.
The pronator teres is a significant muscle involved in various physiological processes and sports activities. Its primary function of pronating the forearm contributes to our ability to perform everyday tasks and participate in sports that require forearm movements.
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Pronator quadratus
The pronator quadratus is a thin, short, flat, quadrilateral muscle that is located in the distal forearm. It is the deepest muscle in the anterior (flexor) compartment of the forearm. It is part of the deep group of forearm flexors, which also includes the flexor digitorum profundus and flexor pollicis longus. The pronator quadratus is located underneath these two muscles and is covered by the interosseous membrane.
The muscle fibres of the pronator quadratus run in a parallel direction, perpendicular to the direction of the arm. They extend across the distal parts of the radius and ulna, with the superficial head of the muscle originating from the anterior distal aspect of the diaphysis (shaft) of the ulna and inserting into the anterior distal diaphysis of the radius. The deep head has the same origin but inserts proximal to the ulnar notch. The pronator quadratus is the only muscle that attaches only to the ulna at one end and the radius at the other.
The main function of the pronator quadratus is forearm pronation, which is the action of turning the forearm and palm so that the palm faces downwards. This movement is essential for activities such as writing or typing on a computer. The contraction of the pronator quadratus pulls the distal end of the radius over the ulna, resulting in the pronation of the radioulnar joint.
The pronator quadratus is innervated by the anterior interosseous nerve of the forearm, with contributions from C7 and C8 spinal nerves. The anterior interosseous nerve is a branch of the median nerve, which arises from the brachial plexus. The muscle receives arterial blood from the anterior interosseous artery, a branch of the common interosseous artery.
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Flexor carpi radialis
The flexor carpi radialis is a muscle in the human forearm that acts to flex and radially abduct the hand. The Latin root "carpus" means wrist, hence flexor carpi is a flexor of the wrist. This muscle is located in the anterior forearm, in the flexor compartment of the forearm, along with the pronator teres, flexor carpi ulnaris, palmaris longus, and flexor digitorum superficialis muscles. All these muscles share the function of flexing the hand on the wrist.
The flexor carpi radialis originates from the medial epicondyle of the humerus, via the common flexor tendon, and surrounding fascia (antebrachial fascia and intermuscular septa). This common flexor tendon is also a common origin for the six long flexor muscles in the forearm: palmaris longus, flexor carpi ulnaris, pronator teres, flexor digitorum superficialis, flexor digitorum profundus, and flexor carpi radialis itself. From the medial epicondyle, the muscle belly courses obliquely, crossing from the ulnar to the radial part of the forearm. In the lower third of the forearm, it gives off a long tendon that passes below the flexor retinaculum into the palmar surface of the hand. The muscle is inserted at the bases of the second and third metacarpal bones.
The flexor carpi radialis is supplied by a branch arising high in the forearm from the anterior or posterior recurrent ulnar arteries. The rest of its nutritional needs are fulfilled by 6-8 branches of the radial artery. Innervation to the flexor carpi radialis comes from the medial and lateral cords of the brachial plexus via the median nerve (C6, C7).
The flexor carpi radialis is a dynamic scaphoid stabilizer. The FCR tendon uses the scaphoid tuberosity as a pulley to reach its distal insertion onto the second metacarpal. It has been hypothesized that FCR muscle contraction generates a dorsally directed vector that resists the scaphoid from rotating into flexion.
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Brachialis
The brachialis is a muscle in the upper arm that flexes the elbow. It is the prime mover of elbow flexion, generating about 50% more power than the biceps. It is also known as the workhorse of the elbow. The brachialis is the only pure flexor of the elbow joint, producing the majority of force during elbow flexion. It is not affected by pronation or supination of the forearm.
The brachialis is located in the anterior compartment of the arm, deep to the biceps brachii and makes up part of the floor of the region known as the cubital fossa (elbow pit). It originates from the anterior aspect of the distal humerus and inserts onto the tuberosity of the ulna. The muscle is innervated by the musculocutaneous nerve and occasionally receives additional innervation from the radial nerve.
The brachialis is a broad muscle, with its broadest part located in the middle rather than at either of its extremities. It is sometimes divided into two parts and may fuse with the fibres of the biceps brachii, coracobrachialis, or pronator teres muscles. The brachialis is the major flexor of the elbow and has a large cross-sectional area, providing it with more strength than the biceps brachii and the coracobrachialis.
The brachialis can be commonly injured by repetitive forceful contractions or muscular contractions with the arm in hyperextension. This is often seen in climbers due to the pronation of the hand and the extended starting position. Physical activities that involve a lot of pull-ups, curls, and rope climbing can also cause brachialis muscle pain. A strain to the brachialis tendon can cause a patient to present with a lacking elbow extension due to painful end-range stretching of the tendon.
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Brachioradialis
The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by way of the brachioradialis tendon, and to the lateral supracondylar ridge of the humerus. The muscle has a fusiform shape, widening at the muscle belly and narrowing distally to insert via a thin tendon at its attachment site. The brachioradialis is the most superficial muscle on the radial side of the forearm. It forms the lateral side of the cubital fossa, or elbow pit.
The brachioradialis is considered a posterior or extensor-compartment muscle, though it functions as a flexor. This unique muscle is one of two forearm extensor-compartment muscles that do not cross the wrist, the other being the supinator. The brachioradialis flexes, pronates, and supinates the forearm but is innervated by the radial nerve. Therefore, weakness of this muscle or its tendon reflex during neurologic examination may indicate a radial rather than a median or ulnar nerve lesion. Trauma and chronic overuse are the usual causes of brachioradialis impairment. In surgery, the brachioradialis is vital to hand defect reconstruction, forearm tendon transfers, and carpal tunnel release.
The brachioradialis is one of the first muscles to recover following radial nerve injury. The brachioradialis arises with the extensor carpi radialis longus muscle from the lateral humeral supracondylar ridge. The brachioradialis is one of seven muscles in the forearm's superficial layer that attach to the lateral epicondyle and supracondylar ridge of the humerus. The muscle is used to stabilize the elbow during rapid flexion and extension while in a midposition, such as in hammering. The brachioradialis is synergistic with the brachialis and biceps brachii; the triceps brachii and anconeus are antagonistic.
The brachioradialis flexes the forearm at the elbow, especially when quick movement is required and when a weight is lifted during slow flexion of the forearm. When the forearm is pronated, the brachioradialis tends to supinate as it flexes. In a supinated position, it tends to pronate as it flexes. This also assists the biceps brachii. The brachioradialis is a stronger elbow flexor when the forearm is in a midposition between supination and pronation at the radioulnar joint.
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Frequently asked questions
The muscles that pronate the elbow include the pronator teres, pronator quadratus, and flexor carpi radialis.
The pronator teres pronates the forearm and assists in flexion of the elbow joint. It works the hardest when the elbow flexes while the hand simultaneously pronates.
The flexor carpi radialis is a forearm muscle that pronates the elbow. It acts alongside the supinator muscle, which is used most when the arm is straight and the forearm is turned outwards.
