Abstract
Experiments were performed on twelve young, healthy males. The subjects were asked to step in accordance with acoustic stimuli with a cyclic time of 1.2 s, while EMGs were recorded with surface bipolar electrodes from the vastus lateralis and medialis, semitendinosus, biceps femoris, tibialis anterior, and medial and lateral gastrocnemius muscles. An electrical stimulus consisting of 5 train pulses (duration : 1 ms, frequency : 300 Hz, 1.5 times perceptual threshold) was applied randomly to either the sural or posterior tibial nerve at the ankle joint during various stepping phases. In general, polyphasic reflex responses were elicited by the peripheral nerve stimulation. The reflex response of flexor muscles showed facilitation followed by inhibition, while that of extensor muscles showed inhibition followed by facilitation with either type of nerve stimulation. However in the case of sural nerve stimulation, inhibition followed by facilitation was observed during the early stance phase in the semitendinosus and biceps femoris muscles, which work as extensors during this phase. The effects of posterior tibial nerve stimulation on the femoral muscles during the stance phase were weak as than those of sural nerve stimulation. The amplitude of the reflex response changed depending on both the EMG activity of each muscle and the joint angle of the lower limb during stepping. It is suggested from these results that sensory inflow from the sole controls stepping, and that bifunctional muscles play an important role in the maintenance of equilibrium using peripheral inflow during stepping.
