Balance control strategy of human body standing on a cart driven by harmonic vibration

Abstract

Assessment and improvement of balance ability is an important issue in the medical field. The balance ability should be divided into static balance ability and dynamic balance ability, and it is necessary to notice the dynamic balance ability from the viewpoint of fall prevention. This paper focuses on the cyclic sway test of a support surface in standing at a single frequency. Although it is known that the balance strategy varies with the frequency in this test, there is no rational explanation based a mechanical model. The purpose of this study is to investigate rational balance strategies from the sway test at 0.3 Hz and 0.8 Hz. We defined a double inverted pendulum model as a mechanical model and two dynamical modes describing the ankle joint strategy and the hip joint strategy. From the superposition of these modes, the head displacement which is one of the control target was obtained. As a characteristics of the balance strategy, we found that only the ankle strategy mode was used at 0.3 Hz. To investigate the control strategy at the frequency, the ankle joint moments were significantly smaller than theoretical values for suppressing the head oscillation. We concluded that the difference is due to the constraint of the base of support, and as a result, the head was oscillated at 0.3 Hz.