The brachioradialis is a prominent skeletal muscle located in the forearm, often visible as the bulk of tissue near the elbow, on the thumb-side of the arm. It is the most superficial muscle within the lateral compartment of the forearm. Originating high up on the humerus (the upper arm bone) and extending down to the wrist area, its long, spindle-shaped structure defines the transition between the upper arm and the forearm.
Defining the Attachment Points
The name “brachioradialis” indicates its two points of attachment: the brachium (upper arm) and the radius (forearm bone). The muscle’s origin is the lateral supracondylar ridge of the humerus, the raised bony line on the outer side of the upper arm bone, just above the elbow joint. This origin covers the proximal two-thirds of this ridge.
From this high point, the muscle extends downward across the elbow joint, forming a long tendon in the lower forearm. The insertion point is the lateral surface of the distal end of the radius, attaching near the styloid process of the radius, the small, pointed bony projection on the thumb-side of the wrist.
The muscle receives motor innervation from the radial nerve, a branch of the brachial plexus, primarily derived from the C5 and C6 spinal segments. Because it is innervated by the radial nerve, the brachioradialis is classified anatomically as a muscle of the posterior (extensor) compartment of the forearm, even though its bulk is visible from the front.
Primary Actions and Contribution to Movement
The primary function of the brachioradialis is to flex the elbow joint, working alongside the deeper brachialis and the biceps brachii. The muscle’s mechanical advantage makes it an effective elbow flexor, especially when the forearm is in a neutral position, often described as the “mid-prone” or “mid-supinated” state, such as when holding a hammer or a cup.
The brachioradialis also rotates the forearm back toward this neutral position. If the forearm is fully pronated (palm down), the muscle acts to supinate it (turn the palm up) as it flexes the elbow. Conversely, if the forearm is fully supinated (palm up), the muscle assists in pronating it (turning the palm down) during flexion.
The brachioradialis plays a significant role in stabilizing the elbow joint during rapid or forceful movements, such as lifting or quick extensions. It exhibits high activity during elbow flexion tasks, indicating a consistent role in stabilizing the joint regardless of the forearm’s rotational position. This action is noticeable when performing activities that require the rapid alternation of elbow flexion and extension, like hammering.
Clinical Indicators and Common Injuries
The brachioradialis muscle is assessed through the testing of the brachioradialis reflex, also known as the supinator reflex. A healthcare provider elicits this deep tendon reflex by tapping the muscle’s tendon near its insertion point on the radial styloid process. A normal response is a slight flexion and supination of the forearm.
Testing this reflex helps medical professionals evaluate the integrity of the radial nerve and the C5 and C6 spinal nerve roots. An abnormal or absent reflex can be a neurological indicator of a problem, such as a spinal cord lesion or nerve damage at those specific cervical levels. The muscle is also important in diagnosing radial nerve injuries, as it is often one of the first muscles to show recovery after damage to the nerve in the upper arm.
The brachioradialis can be secondarily involved in conditions like lateral epicondylitis, commonly known as tennis elbow. This is because the muscle shares fascial connections and is part of the “mobile wad” of muscles that work closely with the wrist extensors. Repetitive overuse, particularly in activities involving forceful gripping and forearm rotation, can lead to muscle strain or tendonitis at its tendon near the wrist.