Variables in recording motor conduction of the radial nerve.

Motor conduction examinations of the right radial nerve were performed on 25 healthy students. The purposes of this study were to determine the optimum position for placement of the active recording electrode, to determine the optimum position of the elbow during conduction examinations, and to report normal values for radial motor nerve characteristics. The radial nerve was stimulated at the supraclavicular notch, axilla, lateral surface of the brachium, and over the middle third of the forearm. The evoked responses were recorded from the abductor pollicis longus or the extensor pollicis brevis. The optimum site for placement of the active recording electrode was found over the medial aspect of the abductor pollicis longus or the extensor pollicis brevis and at a point that represents 28 percent of the forearm length. The optimum position for the elbow was full extension. The distal latency of 2.6 msec, the velocity of the brachium-forearm segment of 50 meters per second, and amplitude of muscle action potentials of 4.0 mv may serve as the limits of normal values for motor conduction of the radial nerve.