A new indirect method for measuring spinal conduction velocity in man

A non-invasive, indirect method for measuring spinal cord mixed afferent-efferent conduction is described. The method is based upon eliciting late reflex responses labelled R1 and R2 from voluntarily contracting thenar and tibialis anterior muscles by preferentially stimulating median and common peroneal sensory nerve fibres. The mean onset latencies of R1 measured 27.5 msec and 30.6 msec recorded from hand and leg muscles respectively. R2 mean onset latencies measured 46.0 msec and 65.1 msec respectively. R1 has characteristics similar to an H-reflex. R2 is a long-loop reflex of unknown pathway assumed to involve similar circuits and rostral turn around points when elicited by both arm and leg stimulation. Mean spinal cord conduction time between the seventh cervical and fifth lumbar spinous processes, is given by (formula; see text) It measured 7.95 msec and the calculated mean conduction velocity was 57.9 +/- 5.7 m/sec.