Influences of h and medium latency reflex responses of the soleus muscle while receiving with malleolus vibration during upright standing

[Purpose] This study investigated whether afferent signals from ankle articular receptors affect the reflexive activity of the soleus muscle of participants while standing upright. [Methods] The subjects, 14 male healthy adults, stood in an upright position on an electric tilting table. Vibrations (about 90 Hz) were applied to the medial and lateral malleolus of the pivot leg (left leg of all subjects), and for the control condition the vibrators were turned off. The maximum M, H and medium latency reflex amplitudes and latencies were extracted from collected M, H and medium latency reflex (MLR) waves under both conditions. The mean amplitudes and latencies of maximum H and MLR were normalized using each subject's maximum M and height, respectively. [Results] The amplitudes and latencies of maximum H and MLR significantly decreased and were delayed under the malleolus vibration condition compared to the control condition. [Conclusion] We conclude that disynaptic inhibition of group I and II afferent fibers from the ankle joint provoke a decrease in the excitation of the α motoneurons of the soleus. It seems that a supraspinal center hardly regulates the excitability of the α motoneurons of the soleus or group II interneurons when the subject can predict how to maintain standing stability.