Effects of positional changes on F wave.

Supine and after standing F wave studies were performed in 22 healthy subjects, in 14 patients with L5 root compression and in 11 patients with low back pain. Unlike previous works, the latency of the F minimal wave, F maximal, F mean and F chronodispersion before and after standing are similar. It is possible that the positional changes of the F wave may be of clinical interest only in sub-groups of patients and the usefulness of further studies is stressed.