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The elbow is a complex joint formed by the articulation of three bones: the humerus, ulna, and radius. This joint allows for a wide range of movements, including flexion, extension, supination, and pronation. The muscles responsible for these movements are broadly grouped into flexor and extensor groups. While the flexor muscles, such as the biceps brachii and brachialis, enable flexion or bending of the elbow, the extensor muscles are crucial for extending the elbow. The primary extensors of the elbow are the triceps brachii and the anconeus, which work together to straighten the arm. These muscles are often engaged in pushing motions and collaborate with shoulder flexors to achieve specific movements. Understanding the anatomy of the elbow and the roles of these muscles is essential for maintaining joint health and preventing injuries.
| Characteristics | Values |
|---|---|
| Muscles that extend the elbow | Triceps Brachii, Anconeus, Deltoid |
| Muscles that flex the elbow | Brachialis, Biceps Brachii, Brachioradialis |
| Muscles that extend the forearm | Extensor Carpi Radialis Longus, Extensor Carpi Radialis Brevis, Extensor Digitorum |
| Muscles that flex the forearm | Flexor Carpi Radialis, Flexor Carpi Ulnaris, Palmaris Longus, Flexor Digitorum Superficialis |
| Nerve supplying the muscles that extend the elbow | Radial nerve |
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What You'll Learn
Triceps Brachii
The triceps brachii is a large, thick muscle on the dorsal part of the upper arm. It often appears in the shape of a horseshoe on the posterior aspect of the arm. The triceps brachii is the only muscle in the posterior compartment of the arm. It is a three-headed muscle, consisting of a long, medial, and lateral head. The long head originates from the infraglenoid tubercle of the scapula, while the lateral and medial heads originate from the humerus. The three heads converge into a single tendon, which attaches to the proximal portion of the olecranon process (the bony prominence of the elbow) located on the upper portion of the ulna.
The triceps brachii is the primary muscle responsible for extending the forearm at the elbow joint. It works in conjunction with the anconeus, a much smaller muscle, to increase the angle between the humerus and the ulna and radius, straightening the arm. The triceps brachii also plays a role in stabilising the elbow joint during fine movements of the forearm and hand, such as writing. Additionally, the long head of the triceps brachii contributes to the extension and adduction of the arm at the shoulder joint.
The triceps brachii can be trained through various strengthening exercises, including isolation and compound movements. Isolation exercises include lying triceps extensions, behind-the-back arm extensions, cable push-downs, and standing triceps "kickbacks." Compound exercises involve pressing movements, such as push-ups, bench presses, tricep dips, and military presses. The triceps brachii can also be contracted statically to maintain a straight arm against resistance.
The triceps brachii is innervated by the radial nerve, which provides a separate branch for each head. The C6 root value of the radial nerve innervates the lateral head, C7 innervates the long head, and C8 supplies the medial head. According to some studies, the medial head may also be partially innervated by the ulnar nerve, while the long head may be partially innervated by the axillary nerve. The muscle receives its arterial supply from the deep brachial artery, a branch of the brachial artery, and is also supplied by ulnar collateral arteries. The venous drainage is provided by the brachial vein.
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Anconeus
The anconeus is a small, triangular muscle located at the elbow, attaching the humerus and ulna. It is considered a continuation of the triceps brachii muscle, with its fibers often being partially or completely blended together. The anconeus originates on the posterior surface of the lateral epicondyle of the humerus and inserts distally on the superior posterior surface of the ulna and the lateral aspect of the olecranon.
The anconeus is an extensor muscle of the forearm, working together with the triceps brachii to increase the angle between the humerus and the ulna and radius, straightening the arm. This muscle is active during elbow extension, but its importance for this movement is likely very small compared to the triceps brachii, which is the major muscle responsible. The anconeus also provides support for the dorsal joint capsule and the ulna.
The anconeus is innervated by a branch of the radial nerve (cervical roots C6-C8), which arises at the radial sulcus of the humerus. Trauma to the nerve supply of the anconeus can result from a shoulder dislocation, fractures of the upper humerus or olecranon, or any injury damaging the radial nerve. This can paralyse the anconeus and other elbow and wrist extensors.
An anatomical variation of the anconeus, called the anconeus epitrochlearis muscle, is found in about 34% of humans. This variation originates at the medial epicondyle of the humerus and can cause a compression of the ulnar nerve, resulting in cubital tunnel syndrome.
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Brachialis
The brachialis is a muscle in the upper arm that flexes the elbow. It is the primary flexor of the elbow and is found mainly in the upper arm between the humerus and the ulna. 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 and does not participate in pronation and supination due to its lack of attachment to the radius. The brachialis is the prime mover of elbow flexion, generating about 50% more power than the biceps.
The brachialis is located on the anterior surface of the shaft of the humerus, deep to the muscle belly of the biceps brachii and distally to its tendon. The biceps brachii muscle is located immediately anterior to the brachialis, as are the brachial vessels, the musculocutaneous, and median nerves. The humerus and the capsule of the elbow joint lie posterior to the muscle. The brachialis is innervated by the musculocutaneous nerve, and commonly also receives additional innervation from the radial nerve. The radial nerve descends in the groove between the brachialis and brachioradialis muscles, above the elbow. The brachialis is supplied by muscular branches of the brachial artery and by the recurrent radial artery.
The brachialis often has a dual innervation – medially innervated by the musculocutaneous nerve and laterally by the radial nerve. The majority of the motor supply is supplied by the musculocutaneous 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 muscle of choice for essentially all elbow flexion activities, whether performed against small or large resistance, or with the forearm held pronated, neutral, or fully supinated.
The brachialis can be commonly injured by repetitive forceful contractions or muscular contractions with the arm in hyperextension. This is commonly seen in climbers, due to the pronation of the hand and the extended starting position. Physical activity that involves a lot of pull-ups, curls, and rope climbing can also initiate brachialis muscle pain. A strain to the brachialis tendon can also cause a patient to present with a lacking elbow extension due to painful end-range stretching of the tendon.
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Biceps Brachii
The biceps brachii (BB), commonly known as the biceps, is a large, thick muscle on the front of the upper arm, between the shoulder and the elbow. It is one of the chief muscles of the arm and is involved in several movements of the arm. The biceps brachii is composed of a short head and a long head, which originate from the apex of the coracoid process and the supraglenoid tubercle of the scapula, respectively. Both heads join to form a single muscle belly, which attaches to the upper forearm.
The biceps brachii works across three joints: the glenohumeral, elbow, and radio-ulnar joints. In the elbow joint, the muscle bends the forearm (flexion) and rotates it outwards (supination). The supination action of the biceps brachii turns the palm upwards and is particularly powerful in a flexed elbow. The biceps brachii is aided in this action by the supinator muscle. The supination function of the biceps is also important in activities such as opening a bottle with a corkscrew.
The biceps are involved in various tasks, including lifting, sports involving throwing and racket use (e.g. baseball, cricket, badminton, and tennis), and gesturing. The muscle is also responsible for abduction (bringing the arm out to the side) and assists with horizontal adduction (bringing the arm across the body). The short head of the biceps brachii helps stabilise the shoulder joint when carrying heavy weights.
The biceps brachii is supplied by the musculocutaneous nerve C5, C6, and C7, and receives blood supply from the muscular branches of the brachial artery. The biceps brachii is a two-joint muscle, and in the shoulder joint, the two muscle heads partially enforce opposite movements. The long head pulls the arm away from the trunk (abduction) and turns it inwards (inward rotation), while the short head pulls the arm back towards the trunk (adduction).
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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 a fusiform muscle, widening at the muscle belly and narrowing distally to insert via a thin tendon at its attachment site. It is the most superficial muscle on the radial side of the forearm.
The brachioradialis 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. It is also known as supinator longus. It forms the lateral side of the cubital fossa, or elbow pit. Despite the bulk of the muscle body being visible from the anterior aspect of the forearm, the brachioradialis is a posterior compartment muscle and is, therefore, innervated by the radial nerve.
The brachioradialis is one of the first muscles to recover following radial nerve injury. It is also used to test the C6 spinal nerve root. It is one of seven muscles in the forearm's superficial layer that attach to the lateral epicondyle and supracondylar ridge of the humerus. The brachioradialis is synergistic with the brachialis and biceps brachii; the triceps brachii and anconeus are antagonistic.
The brachioradialis is active during elbow flexion, whether the forearm is supinated, neutral, or pronated. It is a stronger elbow flexor when the forearm is in a midposition between supination and pronation at the radioulnar joint. It is effective mainly when the brachialis or the biceps have already partially flexed at the elbow.
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Frequently asked questions
The triceps brachii and the anconeus are the muscles that extend the elbow. They are often engaged in activities involving pushing motions.
The triceps brachii is a long muscle that runs from the scapula to the ulna. It is one of the extensors of the forearm and works to increase the angle between the humerus and the ulna and radius, straightening the arm.
The triceps brachii also fixes the elbow during fine movements and is involved in any type of heavy pushing activity, such as a push-up or pushing up from a seated position.
