Effects of Mechanical Stimulation of Knee Joint Mechanoreceptors on Firing of Quadriceps Motor Units

Abstract

In the past, experiments performed to observe the effects of joint afferents on motor control have relied on monosynaptic reflex testing (Skoglund, 1956; Grigg, Harrigan and Fogarty, 1978) or electrical stimulation of joint nerves (Lundberg, Malmgren and Schomburg, 1978). Although these experiments demonstrated that joint receptors make reflex connections with motoneurones supplying lower limb muscles, the observed effects tended to be weak and somewhat variable. This could have arisen because these approaches might not be suitable for determining the effects of a natural pattern of reflex actions arising from joints on motor control. The present experiments use a new technique involving periodic mechanical stimulation of only a few joint afferents whilst recording from tonically discharging motor units. Sensitive statistical tests are then employed to obtain frequency- and time-domain measures of the association between the separate joint afferent and motor unit spike trains. These experiments do not rely on the methodological assumptions inherent in previous experiments and the statistical tests allow more powerful measures of association to be obtained than from simple cross-correlations.