A Methodology for Examining the Chaotic Behavior of the CoP Signal during the Quiet Standing Based on Empirical Mode Decomposition Method

Document Type: Article


1 Department of Biomedical Engineering, Islamic Azad University of Mashhad, Mashhad, Iran

2 Research Center of Biomedical Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran

3 Department of Electrical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Iran


A key parameter for analyzing the human balance dynamics during standing is the center of pressure (CoP). But, so far no conclusive idea has been posed with respect to elicited dynamics of the CoP signal during quiet standing. In this paper, a heuristic algorithm has been proposed to prove the chaotic behavior of the CoP signal with high confidence. In the proposed algorithm, at first the deterministic and non-deterministic (may be stochastic or may be chaotic) components of CoP signal are 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 are computed. Then according to the quantitative value of the computed features, the chaotic component is selected among the extracted components. Finally, using the recurrence quantitative analysis (RQA), the selected chaotic component is reanalyzed to give assurance of correct selecting the chaotic component. In this manner, the kind of CoP dynamics can be determined with high confidence. The analyzed CoP signals were recorded through some experiments on 12 healthy subjects being between 20 to 70 years old. The results of this study show that CoP is a chaotic signal whit high confidence.