Extensor carpi radialis longus muscle

Extensor carpi radialis longus is one of the five main muscles that control movement at the wrist. This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the 2nd metacarpal.

It initially runs along with brachioradialis, but becomes mostly tendon early on, running between brachioradialis and extensor carpi radialis brevis.

Function
As the name suggests, this muscle is an extensor at the wrist joint, and travels along the radial side of the arm, so will also abduct the hand at the wrist. That is, it manipulates the wrist so as to move the hand towards the thumb and away from the palm.

Origin and insertion
It arises from the lower third of the lateral supracondylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the common tendon of origin of the Extensor muscles of the forearm.

The fibers end at the upper third of the forearm in a flat tendon, which runs along the lateral border of the radius, beneath the Abductor pollicis longus and Extensor pollicis brevis; it then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the Extensor carpi radialis brevis, immediately behind the styloid process. It is inserted into the dorsal surface of the base of the second metacarpal bone, on its radial side.

Innervation
Being an extensor contained in the forearm, it is innervated by the radial nerve.

Exercises
The muscle, like all extensors of the forearm, can be strengthened by exercise that resist its extension. A wrist roller can be used and reverse wrist curls with dumbbells can performed.