The influence of vibratory stimulation on the nociceptive component of the lower limb flexion relfex in man /

The nociceptive component of the flexion reflex (FR) has been observed by several investigators to be a reliable physiological manifestation of pain perception in man. It has thus been used as an index of spinal nociceptive activity to study analgesic mechanisms. Vibration is one analgesic procedure which has been reported to decrease subjective pain report in certain pain conditions. The objective of this study was thus to quantitatively investigate the behavior of the human FR during segmental peripheral conditioning with high-frequency vibration.A first study was undertaken to determine the relationship between pain sensation and the FR under the paradigm developed in this laboratory. Visual analogue scale (VAS) ratings of subjective sensation were found to bear a high, linear correlation with stimulus intensity (r = 0.95) and with FR area (r = 0.91).In the main study, we found segmental vibration to inhibit the FR in 5 of 9 subjects. The modulatory effects displayed a slow onset and decay, lasting beyond the 30 min vibration period. Maximum modulation occurred late into vibration, and in some cases after vibration. The direction and magnitude of modulatory effects were basically the same in both biceps femoris (BF) and tibialis anterior (TA) muscles. Our results raised the possibility that prolonged vibration could influence spinal nociceptive reflexes in ways similar to the vibration-induced pain relief described in the clinical literature