An Analysis of the Reverse Reaction Phenomena in Shifting Human Body Weight

Abstract

The reverse reaction phenomena are observed in the output signal (difference between right and left vertical floor reaction force) of the tracking motion, in which a subject shifts his body weight right or left according to a step signal. This paper describes cause and property of the phenomena. A simple model of the tracking motion is constructed assuming that a human body can be approximated with rigid link system. The tracking model can simulate the experimental data well. An unstable pole of standing posture model becomes to be a zero point in the right half-plane on the complex plane in the closed loop transfer function obtained from the tracking model. It is con-cluded that the phenomena result from un-stableness of standing posture. The explanation of the phenomena using the model is certified by electromyogram. Investigating relations between an amplitude of the reverse reaction and other parameters on the basis of simulation results, it is concluded that the amplitude of the reverse reaction is an important parameter from which muscle torque can be evaluated.