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Dynamic Patterns of Postural Fluctuations during Quiet standing: a Recurrence Quantification Approach

When standing quietly, the human body is continuously moving about an upright posture in an erratic fashion. Conventional posturographic analyses that ignore structure of postural steadiness time series do not fully characterize properties of sway dynamics. Recurrence quantification analysis is a technique that can extract the dynamics of postural fluctuations through several variables. In this study, standing-still-sway dynamics of intact and deteriorated postural control systems were investigated by recurrence quantification of stabilograms. The results indicated that both normal and changed postural fluctuations time series, despite erratic and irregular appearance, contain a hidden structure. Although the two components of postural sway originated from an integrated control system, they exhibit distinct dynamical patterns. More determinism, greater local stability, higher degrees of nonstationarity and more laminar states were observed in fore-aft movements. Our findings reveal that decay of postural control mechanism affects dynamical properties of postural control system (especially along mediolateral direction because of the type of impairment). Determinism, nonstationarity and rigidity of balance program as well as laminar states characteristics were increased due to deterioration of postural control system. These findings imply that these measures not only can be used as the pathologic measures to discriminate between group differences, but also provide new openings to understand the nature of postural sway.