Differential effects on tonic and phasic reflex mechanisms produced by vibration of muscles in man.

There is evidence that transmission of the vibration wave set up by percussion in human subjects is responsible for reflex 'spread' or 'irradiation' (Lance and de Gail, 1965). The afferent pathway for reflex contraction of muscles involved in the irradiated response originates in the muscles concerned, and the latency of such a reflex is consistent with the propagated vibration wave being the adequate stimulus. The inference that muscle spindles are responsive to vibratory stimuli is supported by animal experimentation (Echlin and Fessard, 1938; Granit and Henatsch, 1956; Bianconi and Van der Meulen, 1963). During the course of investigation of the spread of reflexes, an attempt to initiate phasic reflexes by applying a mechanical vibrator to muscle was unsuccessful, probably because the stimulus was not of sufficient brevity or intensity to produce a synchronous afferent volley. However, two interesting observations were made concerning the effect ofmore prolonged vibration. Mechanically elicited phasic reflexes (tendon jerks) were found to be depressed while the vibrator was applied to the appropriate muscle, and, in most instances, a gradual involuntary contraction developed in the muscle vibrated. A preliminary report of these findings was presented at the annual meeting of the Australian Association of Neurologists in 1964 (Lance, 1965). It has recently come to our notice that Hagbarth and Eklund have been investigating tonic contraction of muscle evoked by vibration of tendon (Eccles, personal communication) and reported the results to the first Nobel symposium in Stockholm in 1964 (Hagbarth and Eklund, 1965). The present paper analyses the phenomena of phasic reflex depression and tonic contraction produced by vibration of muscle.