Brachioradialis
The brachioradialis is the thick ridge of muscle on the thumb side of your forearm, just below the elbow. It bends the elbow, and it is the muscle that makes a hammer curl feel different from a normal one.
The brachioradialis starts on the outer edge of the upper arm bone above the elbow and runs down the thumb side of the forearm to end near the wrist. It is easy to find on yourself: hold your arm out with your thumb up and bend the elbow against resistance, and the muscle that stands out on top of the forearm near the elbow is this one.
It is a genuine oddity. It sits in the extensor compartment of the forearm, it is supplied by the radial nerve like the extensors, and by every anatomical grouping it belongs with them — yet it flexes the elbow, which is the opposite of what its neighbours do. It is sometimes called the beer-raising muscle for exactly that reason.
How much of a flexor it really is has been argued about for a long time. One view treats it as a straightforward elbow flexor that is simply strongest in the neutral position; another treats it primarily as a shunt muscle, pulling the forearm bones along their length into the elbow joint to stabilise it against the pull of the other flexors, with flexion as a secondary effect. Both views appear in the literature and the disagreement is real rather than a matter of phrasing.
Either way, what is not in dispute is when it works hardest: with the forearm neutral, thumb pointing up, and the elbow moving at speed or under load.
Training notes
Hammer curls are the movement most associated with it and the association is correct. The neutral grip is where it has the best mechanical advantage, and it is doing a large share of the work in that position alongside the brachialis.
Reverse curls, with the palms facing down, also load it well and add wrist extensor work at the same time. They are usually done with substantially less weight than a normal curl, which is expected rather than a problem.
It gets loaded in every carry and every pulling movement performed with a neutral or pronated grip, so it is a muscle that develops quietly in people who do a lot of rowing and carrying without ever being trained directly.
It contributes most of the visible size of the upper forearm near the elbow, so it is the muscle doing most of the work in what people generally mean by forearm development from the front.
Anatomy
- Origin
- Upper two-thirds of the lateral supracondylar ridge of the humerus
- Insertion
- Lateral surface of the distal radius, proximal to the styloid process
- Actions
- Flexes the elbow, with greatest effect when the forearm is in mid-pronation
- Rotates the forearm toward the neutral position from either extreme
- Innervation
- Radial nerve (C5–C6)
Brachioradialis arises from the upper two-thirds of the lateral supracondylar ridge of the humerus, runs down the radial side of the forearm superficially, and inserts by a long flat tendon on the lateral surface of the distal radius just proximal to the styloid process. It forms the lateral border of the cubital fossa.
It is anomalous in three respects at once: it lies in the posterior, extensor compartment; it is supplied by the radial nerve, which otherwise supplies extensors; and it nonetheless flexes the elbow. In developmental terms it belongs with the extensor group and has migrated anteriorly across the elbow.
Its functional classification is genuinely disputed. It is conventionally listed as an accessory elbow flexor, most effective in mid-pronation where its line of pull is most favourable. An alternative and well-argued view classifies it as a shunt muscle: its distal insertion, far from the joint, means the majority of its force acts along the forearm's long axis, compressing the joint surfaces rather than rotating them, so its principal role would be stabilising the elbow against the distracting force of rapid or loaded flexion. Both accounts appear in current references.
Its action on forearm rotation is limited and directional — it moves the forearm toward neutral from either full supination or full pronation, and cannot carry it past that point.
Under load
It is loaded most directly by elbow flexion in a neutral or pronated grip, since supination removes its mechanical advantage.
It is under continuous load in any carry or hang, consistent with either account of its function.
It is the largest contributor to the bulk of the proximal anterior forearm and is developed substantially by grip and rowing work performed with a neutral grip.
Exercises
No exercise in the library names Brachioradialis yet. Nothing has been invented to fill the gap — a false reference costs more than an absent one.