Postural effects on F wave parameters in lumbosacral root compression and canal stenosis.

The effects of standing, and lying with the back extended, on F wave minimal latency and F chronodispersion were studied in patients with lumbar canal stenosis, lumbosacral root compression syndromes, and low back pain. Standing for 3 min produced increased F chronodispersion in lumbar canal stenosis and root compression syndromes but had less effect on the F minimal latency. In patients with low back pain these variables were unchanged by these postural manoeuvres. These observations illustrate the value of adapting electrophysiological investigations to those clinical features that induce symptoms in these disorders.