The purpose of this study was to investigate electrophysiologic changes of dynamic F waves between rest and postexercise in neurogenic claudication and to evaluate diagnostic sensitivity of dynamic F wave. To improve the sensitivity of F wave, we designed averaging technique after alking for 20 minutes with back extended, and termed it as dynamic F wave. Walking for 20 minutes produced either increased F mean latency and F chronodispersion or unelicitability. These changes after postexercise suggested ischemic induced conduction block and slowing in proximal motor axons. So, we studied 30 healthy controls and 30 patients with neurogenic claudication.

The results were as follows;

1) In control group, conventional conduction studies and dynamic F waves were statistically insignificant.

2) In patient groups, conventional conduction studies were insignificant, but dynamic F waves were statistically significant.

3) Among patient groups, spinal stenosis and lumbosacral radiculopathy had more effect on dynamic F waves than herniated intervertebral disc.

4) Diagnostic sensitivity of dynamic F waves was 40% in patient groups.

In conclusion, dynamic F waves are not sensitive technique in the diagnosis of neurogenic claudication, but it increase the specificity of the electrophysiological investigation in relation to particular clinical features by positional change in spinal stenosis and herniated intervertebral disc.