CAUSALITY IN THE FEEDBACK LOOP DURiNG BALANCING TASKS: INTERMITTENT CONTROL OF QUIET STANDING

Abstract

The aim of this study was to investigate the relationship between the timing of intermittent muscle activity and joint fluctuation and between intermittent muscle activity and joint torque output. Eight healthy male participants stood quietly on the force platform for 120 sec, while we measured angular displacements and joint toque of the ankle, knee, and hip in the sagittal plane. Surface electromyography from six leg muscles of each leg was also recorded to determine phasic muscle activation and deactivation for each muscle by using two low-pass filters. We found that muscle activation and deactivation periods were in accordance with joint position and velocity and were associated with torque fluctuations in the anatomical action direction. These results succeeded in experimentally visualizing the causality of the feedback loop of the postural control mechanism.