Brachioradialis

What it is

A long muscle forming the visible ridge along the thumb side of the forearm, running from the lower outer humerus to the far end of the radius at the wrist.

It is anatomically odd. It sits in the extensor compartment of the forearm and is supplied by the radial nerve, like the extensors — but it flexes the elbow. It is the only muscle supplied by the radial nerve that does.

Its insertion is unusually far from the joint it acts on, right down at the wrist, which gives it a long lever arm at the elbow.

What it does

Flexes the elbow, most effectively when the forearm is in a neutral, thumb-up position.

It is sometimes described as bringing the forearm to a mid-position from either full pronation or full supination, though how much it really contributes to rotation is debated and probably small.

It has a reputation as a muscle of rapid rather than heavy flexion, because of its leverage.

What loads it

Hammer-grip curls and neutral-grip pulling load it most, because those positions suit its line of pull. Palm-down curling loads it too.

The Repertoire has no arm movement yet.

What is commonly got wrong about it

That it is a forearm muscle in the functional sense. It lies on the forearm and moves the elbow. It does nothing at the wrist.

"Forearm size" as a grip-training outcome. Much of the visible mass of the upper forearm is this muscle, and it responds to elbow flexion work rather than to gripping. Grip work builds the deeper flexors.

That it is a minor muscle. It is one of the larger muscles crossing the elbow.