F-wave study at different stimulation rates in upper motoneurone lesions.

F-wave duration, amplitude and persistence at different frequencies of the antidromic impulse (0.2-0.5-1-2 Hz) were determined in 18 patients with vascular hemiplegia and in 32 healthy subjects of both sexes in the same age range. In normal subjects F amplitude and persistence showed a significant increase as the stimulation rate increased; in spastic patients a small difference in F amplitude was only found for greater difference in stimulus frequencies, the persistence did not significantly changed at different stimulation rates. Individual cross-correlation values (r) obtained for latency and duration, latency and amplitude, amplitude and duration did not show significant changes at different stimulation rates in patients and in controls.