F wave

F waves are action potentials that are elicited by the excitation of motor neurons by an antidromically travelling electric impulse applied to the distal part of an extremity. They are therefore assumed to give information about the pathological status of the entire length of the motor nerve fiber and it is possible to investigate the proximal segments of the peripheral nerve with this method. F waves are used in evaluation of peripheral nerves for they may indicate the pathological status of a peripheral nerve more successfully as compared to conventional motor and sensory nerve conduction examinations.

An F wave has a latency (period between the application of electric impulse and the initiation of the peripheral nerve excitation; in miliseconds), an amplitude (height of the wave, provides a rough estimation about the number of activated motor neurones) and duration.

There are various reports on different F wave measurements, especially minimum F wave latency, maximum F wave latency, F chronodispersion (the difference between maximum and minimum F wave latencies), F wave conduction velocity and F tacheodispersion (the distribution of F wave conduction velocities of a nerve fibre estimated from significant numbers of consecutively recorded F waves).