The Static Standing Postural Stability Measured by Average Entropy

Figures

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  Figure 1. An application of the average entropy (AE) and entropy of entropy (EoE) methods. (a) The four original center of pressure (COP) speed time series {vi} recorded from a certain subject under the four kinds of balance conditions, separately. Each series was equally divided into 16 windows with each of 5 data points in a red frame. The Shannon entropy value of the 5 data points in each window in red was calculated individually. (b) The four sets of Shannon entropy sequences {yj(5)} with each of the 16 elements, separately.

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  Figure 2. Analytical procedure flowchart in this study.

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  Figure 3. AE values of the COP speed time series from the 11 subjects under four kinds of balance conditions. Recall that the abbreviations of conditions O2, C2, O1, and C1 stood for bipedal with open eyes, bipedal with closed eyes, unipedal with open eyes, and unipedal with closed eyes, respectively. The symbols of blue triangles, yellow stars, green triangles, and red circles represent O2, C2, O1, and C1 conditions, respectively.

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  Figure 4. (a) EoE values and (b) MSE values of the COP speed time series from the 11 subjects under four kinds of balance conditions: O2, C2, O1, and C1.

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  Figure 5. MSE complexity index (CI) values of COP trajectories time series in (a) mediolateral (ML) direction and (b) anteroposterior (AP) directions from the 11 subjects under four kinds of balance conditions: O2, C2, O1, and C1.

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  Figure 6. The EoE versus AE of the 44 COP speed time series from the 11 subjects under four kinds of balance conditions: O2, C2, O1, and C1.