Median nerve F-wave conduction in healthy subjects.

This study of the normal median nerve was designed to compare techniques of using the shortest and average F-wave latencies, F-wave values between extremities, and F-wave values with the conventional motor response values and to determine the relationships between F-wave latency and arm length. We examined 40 median nerves in 20 subjects with no known pathology. The motor response latency was measured from wrist and elbow stimulation sites by conventional techniques. We then applied multiple stimuli at the same sites to record a series of 10 F-wave latencies and determined shortest and average F-wave latencies. Values of F-wave and M-response conduction are reported. No significant difference was found in F-wave latency or velocity between extremities within subjects, using either the shortest or average latency technique. We propose a formula for calculating the estimated F-wave distal latency based on the conventional motor response distal latency. The F-wave conduction velocities of the forearm were faster and more variable than the motor nerve conduction velocities. A high correlation was found between F-wave distal latency and arm length. Using the method described, the F wave can be a useful measure in evaluating the conduction of proximal segments of peripheral motor nerves.