Abstract
The postural control moment in sagittal plane calculated from the center of foot pressure (COP) was evaluated when the impulsive disturbance was applied by the trank traction. The transfer function, with second order denominator and one order numerator, from the disturbance to the postural control moment was identified using the output error minimum (OEM) method. The DC gain increased from -0.4 to 6.6dB and the natural freqency of the denominator decreased from 1.0 to 0.7Hz with the increase of the disturbance torque ranged from 91Nm to 156Nm. These changes imply nonlinear properties of the postural control system. However, no significant differences were observed in DC gain and the natural frequency while the disturbance torque ranged from 156 to 216Nm. When the forward and backward 156Nm disturbances were applied, the maximal position of COP were MP joint and ankle joint respectively. Therefore, the nonlinear properties are attributed to the foot joint mechanism. Implications of findings are also discussed about nonlinear properties of the foot joint mechanism and the postural controller.
