Anterior view of muscles of the left forearm with Brachioradialis shown in blue.
Cross-section through the middle of the forearm. (Brachioradialis labeled at center left, sixth from the top.)
|Lateral supracondylar ridge of the humerus|
|Distal radius (Radial styloid process)|
|radial recurrent artery|
|Actions||Flexion of Elbow|
|Anatomical terms of muscle|
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.
Distal end of Humerus/styloid process of radius
|This section requires expansion. (December 2013)|
Despite the bulk of the muscle body being visible from the anterior aspect of the forearm, the brachioradialis is a posterior compartment muscle and consequently is innervated by the radial nerve. Of the muscles that receive innervation from the radial nerve, it is one of only four that receive input directly from the radial nerve. The other three are the triceps, anconeus, and extensor carpi radialis longus. (All other posterior compartment muscles that receive radial innervation are supplied by the deep branch of the radial nerve.)
The brachioradialis flexes the forearm at the elbow. 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. When pronated, the brachioradialis is more active during elbow flexion since the biceps brachii is in a mechanical disadvantage.
With the insertion of the muscle so far from the fulcrum of the elbow, the brachioradialis does not generate as much joint torque as the brachialis or the biceps. It is effective mainly when those muscles have already partially flexed at the elbow. 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.
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.
Supination of the forearm being attributed to a function of the brachioradialis was originally hypothesized by Leonardo da Vinci. He expressed the original idea of the biceps acting as a supinator in a series of annotated drawings made between 1505 and 1510 (referred to as his Milanese period); in which the principle of the biceps as a supinator, as well as its role as a flexor to the elbow were devised. However, this function remained undiscovered by the medical community as da Vinci was not regarded as a teacher of anatomy, nor were his results publicly released. It was not until 1713 that this movement was re-discovered by William Cheselden and subsequently recorded for the medical community. It was rewritten several times by different authors wishing to present information to different audiences. The most notable recent expansion upon Cheselden's recordings was written by Guillaume Duchenne in 1867, in a journal named Physiology of Motion. To this day it remains one of the major references on supination action of the biceps brachii.
- Bowden, Bradley S. Bowden, Joan M. An Illustrated Atlas of Skeletal Muscles. 2nd ed. 2002
- Saladin, Kenneth S. Anatomy & Physiology. 4th ed. 2007
- Origin, insertion and nerve supply of the muscle at Loyola University Chicago Stritch School of Medicine
- Illustration: upper-body/brachialis from The Department of Radiology at the University of Washington
- Anatomy figure: 07:01-09 at Human Anatomy Online, SUNY Downstate Medical Center - "Transverse section through the left arm just proximal to the elbow."
- Anatomy figure: 07:03-07 at Human Anatomy Online, SUNY Downstate Medical Center - "Superficial muscles of the anterior (flexor) compartment of the left forearm."
- Anatomy figure: 09:02-02 at Human Anatomy Online, SUNY Downstate Medical Center - "Superficial muscles of the posterior (extensor) compartment of the left forearm."
- lesson5musofpostforearm at The Anatomy Lesson by Wesley Norman (Georgetown University)