H-REFLEX MODULATION DURING REVERSE PASSIVE PEDALING

During passive pedalling or walking movements of the human leg, the ga in of the soleus H reflex is depressed in proportion to the rate of th e movement, with the depression maximal at the end of leg flexion. In this phase, maximum flexion of the hip and knee occur at different pos itions. The question was raised as to whether the gain changes still o ccur when the direction of movement is reversed, thus reversing those positions. In four subjects, reverse passive pedalling movements of th e legs were studied at two velocities, 10 and 30 rpm. Ten H reflexes p er subject were elicited from popliteal fossa stimulation at eight equ ispaced positions around the cycle and M waves were used as an indicat or of stimulation stability. For each subject, reflex attenuation occu rred in the flexion phase, but unlike forward movement, peak inhibitio n occurred before full flexion of the knee. Movement velocity continue d to determine the degree of inhibition. The reverse vs. forward diffe rence in peak inhibition most likely reflects differences in condition ing receptor discharge from hip and knee extensor muscles, due to the differing kinematic profiles for the two movements. Therefore the spin al gain modulation appears to receive significant input from specific somatosensory discharge consequential to the movement. Copyright (C) 1 996 Published by Elsevier Science Ltd.