Abstract
Standing posture regulation system is considered to be complex systems. Body sway appearing in standing posture was investigated from this point of view. The sway of the body center of the gravity in upright standing was recorded with eyes open and closed each 60 seconds using a stabilometer in 10 normal subjects. From time series data obtained, attractor (embedding dimension: 3), correlation dimension, Lyapunov exponent, Lyapunov spectrum and the largest Lyapunov exponent were calculated using a chaos analysis program.Correlation exponent was not saturated on an increase of embedding dimension (from 2 to 7). The result indicated that attractor did not have self-similarity. The result suggests that the irregular fluctuation observed in standing posture is not deterministic chaos.Lyapunov spectrum indicated that nature of attractor was torus and random. The result suggests that the sway appearing in standing posture is constructed from quasi-periodic and random movement.The largest Lyapunov exponent indicated that orbital instability is high in right-left sway than forward-backward sway. The control mechanism of standing posture differs in right-left and forward-backward directions.The analysis considering the complex systems provide information on postural control that cannot be obtained by conventional method.
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