Submaximal stimulation and f-wave parameters

This study evaluates the effect of submaximal stimulation and varying stimulus rates on F-wave parameters.

F-waves were recorded from the abductor pollicis brevis muscle from 3 normal subjects stimulating at 25%, 50%, and 75% intensity in comparison with supramaximal stimulation based on peak-to-peak compound muscle action potential amplitude. The effect of varying stimulus intensity (0.5, 1.0, and 2.0 Hz) at 30% stimulus intensity was also evaluated. Data were evaluated based on "true" values obtained after 100 stimuli. F-wave parameters studied included latencies (minimal and mean), amplitudes, persistences, durations, chronodispersions, and mean F amplitudes/maximum compound muscle action potential amplitudes.

For varying stimulus intensities and rates, the following results were obtained: (1) no meaningful change in F latencies or durations; (2) mean latency values were more reproducible than minimum; (3) amplitudes, persistence, and mean F amplitudes/maximum M-wave amplitude ratios increase linearly with increase in stimulus intensities; (4) chronodispersion increases with increase in stimulus intensity; (5) 20 stimuli appear adequate for true values at supramaximal stimulation but more are needed at submaximal levels; (6) varying stimulus frequency at submaximal stimulation did not meaningfully affect the results.

F-parameters require more stimuli at submaximal stimulation and, except for latencies and durations, would require different normal values than at supramaximal stimulation.