The impact of external perturbations on postural control

Purpose: External factors can disrupt postural control, but the intricate workings of the postural control system enable an appropriate response. This study seeks to assess how external perturbations affect postural control. Methods: Twenty women participated in study, which consisted four trials involved quiet standing and experiencing induced perturbations by being struck with a boxing bag from the back, right, and left sides, respectively. The center of pressure (CoP) path length was recorded for each of the mentioned trials. Sample Entropy (SampEn), Lyapunov Exponent (LyE), and Fractal Dimension (FD) were computed for the CoP time series, separately for the anterior-posterior (AP) and mediolateral (ML) directions. The nonparametric Friedman ANOVA with Dunn-Bonferroni post-hoc analysis was employed to investigate the influence of external perturbations on both linear and nonlinear parameters on postural control. Results: The post-hoc analysis showed for LyE_AP_quiet (1.02 ± 0.18) significantly higher values than for LyE_AP_right (0.92 ± 0.22) and significantly higher for LyE_AP_left. Lyapunov Exponent was the parameter that differentiated the most between samples. Conclusions: The greatest number of significant differences between samples were demonstrated by the Lyapunov Exponent. This nonlinear parameter should be used to evaluate various perturbations during upright position in healthy subjects.