Objective
To determine if stretching the sciatic nerve in control and patients with lumbosacral radiculopathy significantly alters F-wave parameters.

Method
We studied F-waves in the deep peroneal & posterior tibial nerves of 20 patients with unilateral lumbosacral radiculopathies and 22 controls. F-waves were recorded bilaterally in the neutral position and supine in 30^o & 60^o straight leg raising (SLR). F-wave parameters included minimal latency (F min), maximal latency (F max), mean latency (F mean), latency difference between F min and F max (chronodispersion), mean duration (F dur) and side to side difference in F min, F max, F mean and F dur.

Results
In controls, the F-wave latency was found to be longer in supine with SLR than in neutral position. In patients with lumbosacral radiculopathy, significant differences of F max, F mean and F dur between sides during 30^o SLR were noted in the deep peroneal nerves, but all parameters in the posterior tibial nerves during SLR were not changed.

Conclusion
In this study, we observed significant changes in F-wave latency in control during straight leg raising, but no significant changes in patients with lumbosacral radiculopathy. For the clinical application to lumbosacral radiculopathy, further study is needed.