Effects of Short and Medium Latency Reflexes of the Plantae Muscle with Ankle Vibration during Sudden Foot Movement

Abstract

[Purpose] This study examined the influence of signals from ankle joint afferent fibers on the reflexive plantae muscle activity during standing subjects. [Subject] Ten male healthy adults participated in this study. [Methods] The subjects stood with their eyes closed on a movable platform that was moved backward. Vibrators (about 90 Hz) were applied to the medial and lateral malleolus of both legs. The vibrators were turned off in the control condition. In the malleolus vibration (MV) condition, vibration stimulus was applied for one minute before the beginning of trials and was continued during the trials (about six minutes). The short (SLR) and medium latency reflex (MLR) of the flexor digitorum brevis muscle (FDB) electromyogram (EMG) responses of the left leg during the platform translations were measured under the control and MV conditions. [Results] The latencies of the FDB SLR and MLR during MV condition were observed to increase significantly in comparison to the control. The integration EMG response values (iEMG) of the SLR and MLR significantly decreased during MV condition. [Conclusion] Excessive afferent signals from the ankle articular mechanoreceptors may participate in the reduction of the reflexive FDB SLR and MLR activities during standing postural perturbation due to changes in the excitability of inhibitory interneurons.