A methodology for examining the chaotic behavior of CoP signal during quiet standing based on empirical mode decomposition method

Abstract

A key parameter for analyzing the human balance dynamics in the standing position is the Center of Pressure (CoP). However, no conclusive idea has been posed with respect to elicited dynamics of the CoP signal in quiet standing so far. In this paper, a heuristic algorithm was proposed to prove the chaotic behavior of the CoP signal with high confidence. In the proposed algorithm, first, the deterministic and non-deterministic (either stochastic or chaotic) components of the CoP signal were extracted using the Empirical Mode Decomposition (EMD) method. Then, the nonlinear features of the extracted components such as fractal dimension, Lyapunov exponent, correlation dimension, and alpha parameter were computed. Then, based on the quantitative value of the computed features, the chaotic component was selected from the extracted components. Finally, through the Recurrence Quantitative Analysis (RQA), the selected chaotic component was reanalyzed to ensure the correct selection of the chaotic component. In this respect, the kind of CoP dynamics can be determined with high confidence. The analyzed CoP signals were recorded through some experiments on 12 healthy subjects aging 20 to 70 years old. The results of this study indicated that CoP was a chaotic signal with high confidence.