Integration Frequency Response of Human Dynamic Balance Under Passive Motion Stimulus by Using Center of Gravity

Abstract

This study investigated the frequency response of body oscillations in the medio-lateral (M-L) direction during upright stance and proposes an M-L balance assessment method. Previous investigations have commonly used a visual tracking task and measured the displacement of the center of pressure, but these methods are affected by the body’s subjective factors and do not reliably represent human dynamic balance. In this study, 10 subjects were settled on a 6-DOF motion platform in a specific posture, and the passive motion stimulus was tracked using a sinusoidal waveform with a frequency range of 0.05-1.5 Hz. The Bode diagram, which consisted of the magnitude and phase-shift between the motion of platform and the body’s center of gravity (COG), was obtained by measuring the COG displacement. The results show that, at 0.5-1.0 Hz, the subjects had a higher probability of losing their balance. The mean cut-off frequency (COF) was 0.62 Hz, so the bandwidth of the body oscillation was 0.1-0.6 Hz. Furthermore, the COF could be used to quantify balance ability, i.e. a higher COF corresponded to better balance ability. Additionally, the mean resonance frequency was 0.44 Hz, which reflected spontaneous body sway. In conclusion, this study determined the integration frequency response of human dynamic balance under passive motion stimulus using COG, and proposed a more objective and accurate method for evaluating balance ability.