Corrective reactions to stumbling in man: functional significance of spinal and transcortical reflexes.

Stumbling reactions were studied in terms of bilateral leg muscle electromyographic (EMG) responses during locomotion on a treadmill. At random times, but fixed points in the stepping cycle, short impulses were applied to the treadmill, either accelerating or decelerating its progress. It was found that acceleration was compensated for by a strong ipsilateral gastrocnemius and contralateral tibialis anterior activation, and deceleration by a bilateral tibialis anterior activation. In both muscles the responses appeared with a latency of about 70 msec and lasted for about 150 msec. It is concluded that sudden displacements induced by acceleration or deceleration during gait are compensated for by a polysynaptic spinal pathway, with an associated depression of monosynaptic responses.