Brachioradialis muscle

Origin and insertion

The brachioradialis muscle originates from the upper two-thirds of the lateral supracondylar ridge of humerus and the anterior surface of the lateral intermuscular septum of the arm. It slides over the lateral surface of the elbow joint, entering the anterolateral cubital area.

The muscle fibers course inferiorly down the radial part of the anterior forearm, forming a thick tendon in approximately the middle of the forearm. This tendon then traverses the remainder of the forearm, inserting near the wrist, just proximal to the styloid process of radius.

Relations

Brachioradialis is the most superficial muscle on the radial aspect of the forearm. It can be easily recognized and palpated when the forearm is flexed and semi pronated as the fleshy prominence in the upper half of the lateral forearm.  The muscle comprises the lateral wall of the cubital fossa and at the same time presents the border between the anterior and posterior forearm compartments. Its proximal part is medially covered by the distal part of the brachialis muscle, while the tendon of biceps brachii passes deep to it, on its way towards the radial tuberosity. The radial nerve and the arterial anastomosis occurring between the radial recurrent and deep brachial (profunda brachii) arteries pass between the brachioradialis and brachialis. The cephalic vein and lateral cutaneous antebrachial nerve pass over the muscle’s superficial surface. In the mid forearm, the muscle is lateral to flexor carpi radialis. 

At the wrist level, the tendon lies lateral to the radial artery. Note that this is the spot where the radial pulse is palpated. Here also, the superficial branch of the radial nerve arises deep to brachioradialis. It passes between this and the extensor carpi radialis brevis muscle before crossing superficially over the extensor retinaculum to enter the hand. Just proximal to its insertion, the brachioradialis tendon is crossed by the tendons of abductor pollicis longus and extensor pollicis brevis muscles.

To find out more about the extensor muscles of the forearm, including the brachioradialis, take a look below:

Innervation

Brachioradialis is innervated by the radial nerve (from the root values C5-C6) that stems from the posterior cord of the brachial plexus.

Blood supply

Blood supply to the brachioradialis muscle comes from branches of the radial artery, radial recurrent artery and the radial collateral branch of the deep brachial artery.

Function

The brachioradialis muscle works in synergy with biceps brachii and brachialis to flex the forearm at the elbow. Brachioradialis is a powerful forearm flexor when the forearm is semi pronated, meaning that the palm is perpendicular to the ground.

When considering the functional anatomy of the upper limb muscles, we see that all three mentioned flexor muscles work in synergy. Yet their fibers are oriented in a specific way, so that each of them can be a primary flexor depending on the position of the forearm. Focusing on brachioradialis, we see that its proximal attachment is near the elbow joint, while the distal attachment is just proximal to the wrist joint. This feature already gives great potential for a strong and effective forearm flexion, with the muscle working in accordance with the lever mechanism whereby the elbow joint is the fulcrum. 

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Next, since muscles pull the strongest when their fibers are aligned lineary, we can conclude that brachioradialis will exhibit its maximal force when the arm is semi pronated as this is where the muscle’s attachments line up with each other in a sagittal plane. This is why your brachioradialis muscle will work most effectively when lifting a load with a semi-pronated forearm. In contrast to this, biceps brachii pulls the most effectively when the forearm is in a supinated position and brachialis when the forearm is in pronation. These actions are seen in various activities, from picking up groceries to rowing.

You will encounter a statement that brachioradialis also assists supination and pronation. This happens when the forearm is in either one of those two positions, since brachioradialis tends to bring the forearm back into the semi pronated stance. Hence, when the forearm is in a supine position, the muscle will tend to pronate it as far as it reaches a mid-pronated position, and vice versa. It is also worth mentioning that brachioradialis eccentrically contracts to smoothe forearm extension in repetitive activities such as hammering.

Consolidate your knowledge about the brachioradialis and other muscles of the posterior forearm with our quiz below!

Mnemonic

Here's a mnemonic that summarizes the brachioradialis and helps you to remember it.

BrachioRadialis follows the BR rule

• Function: Its the Beer mug Raising muscle (i.e. flexes elbow, strongest when the wrist is held for holding a beer mug.)
• Innervation: Breaks Rule in that it's a flexor muscle, But Radial. (Radial nerve usually is for extensors).
• One relation: Behind it is the Radial nerve in the cubital fossa.