DIFFERENT EFFECT OF HEIGHT ON LATENCY OF LEG AND FOOT SHORT-LATENCY AND MEDIUM-LATENCY EMG RESPONSES TO PERTURBATION OF STANCE IN HUMANS

In standing humans, platform perturbations evoked short- (SLR) and med ium-latency responses (MLR) in soleus (Sol), tibialis anterior (TA) an d flexor digitorum brevis (FDB) muscles. The latency of all responses significantly increased with subjects' height. The slope of the regres sion lines for the MLRs versus height was significantly steeper than t hat for the SLRs. The conduction velocity of the afferent fibres media ting the FDB MLR, calculated on the basis of the regression, was 17.5 m/s. These findings indicate that the MLRs are transmitted through aff erent fibres slower than those mediating the SLRs. While the latter fi bres are spindle group Ia afferents, the former are suggested to be gr oup II fibres.