The extensor carpi radialis longus is one of the five main muscles that control movements at the wrist. (myobuddy.com)
It is found deep to the brachioradialis, extensor carpi radialis longus and brevis, and extensor digitorum. (kingofthegym.com)
More specifically, it occurs when the tendon of one of the forearm muscles, the extensor carpi radialis brevis (ECRB), becomes irritated. (gastownphysiopilates.com)