Phase-dependent modulation of cutaneous reflexes in tibialis anterior muscle during passive stepping

Abstract

The purpose of this study was to determine whether the cutaneous reflex elicited in the tibialis anterior (TA) muscle would be modulated in a phase-dependent manner while human subjects were passively stepping on a treadmill (treadmill stepping) or in the air (air stepping). The passive stepping was produced by a robotic gait trainer, Lokomat. The cutaneous reflexes following electric stimulation to the distal tibial nerve were recorded at ten different phases of a step cycle under the condition of tonic dorsiflexion [10% of maximum electromyography activity (EMGmax)]. Cutaneous reflex EMG responses with peak latencies of 70-120 ms [middle latency responses (MLR)] were then analysed. The results showed that there were no visible differences in the background EMG activities at the ten phases or two passive stepping conditions. During treadmill stepping, however, the magnitude of the facilitatory reflex responses between the late stance and the early swing phase was strongly enhanced, whereas no clear modulation of the MLR during air stepping was observed. These results suggest that the load-related afferent information plays a key role in the modulation of the cutaneous reflex during human walking.