Extensor carpi ulnaris, or ECU, runs along the back and little-finger side of the forearm. It begins from the common extensor origin at the lateral epicondyle and from the posterior ulna, then attaches to the base of the fifth metacarpal. Its name describes its job. It extends the wrist and moves it toward the ulna, which is ulnar deviation. It works with the radial wrist extensors for balanced extension and with flexor carpi ulnaris for ulnar deviation. This coordination helps stabilize the wrist during gripping, racquet sports, golf, throwing, and tool use. The ECU tendon has an important relationship at the wrist. It travels behind the distal ulna through the sixth extensor compartment and is held in place by a subsheath. That structure can become irritated or injured, and a client may report dorsal-ulnar pain or snapping. Snapping after trauma is not something to repeatedly reproduce during a massage assessment. ECU is supplied by the posterior interosseous nerve, primarily roots C7 and C8. This is a motor branch, so new weakness of wrist or finger extension deserves medical assessment. To palpate ECU, support a pronated forearm and ask for gentle wrist extension toward the little-finger side. Follow the muscle and tendon without pressing aggressively over a painful distal tendon. Massage can include broad warming, comfortable longitudinal work, and gentle lengthening toward wrist flexion and radial deviation when appropriate. Remember that ulnar-sided wrist pain has several possible sources, including the triangular fibrocartilage complex, distal radioulnar joint, fracture, tendon instability, and nerve-related problems. Massage therapists do not diagnose these. Refer trauma, deformity, marked swelling, painful snapping, progressive weakness, or persistent symptoms. The study line is simple: lateral epicondyle and posterior ulna to the fifth metacarpal; wrist extension and ulnar deviation; posterior interosseous nerve, C7 and C8.