The complexity of the center of pressure (COP) provides important information regarding the underlying mechanisms of postural control. The relationships between COP complexity and balance performance are not fully established and might depend on the task constraints and the filtering decomposition of the COP signal. This study assessed COP complexity under different task constraints and it was assessed if emergent dynamics of COP fluctuations differ according to fractional components of COP related to peripheral or central adjustments. One hundred and sixty-two participants performed two sitting balance tasks. Accuracy was required by following a target that moved in the mediolateral (ML) or in the anteroposterior (AP) axis. Complexity dynamics of COP were addressed through detrended fluctuation analysis (DFA) in the axis constrained by accuracy requirements and in the one nonconstrained. Decomposition of COP components was applied by low-pass, band-pass, and high-pass filters. DFA of low-pass and band-pass components of COP in the constrained axis were small-to-moderately related (r = 0.190-0.237) to balance performance. DFA of the high-pass component of the COP exhibited the opposite relationship (r = -0.283 to -0.453) in both axes (constrained and nonconstrained). This study evidences that COP complexity is linked to better performance. This positive relationship complexity/performance is observed in the low- and mid-frequency components of the COP. These components might be related to central mechanisms of postural control. The lack of relationships between the different frequencies analyzed in the study suggests that they are capturing different components of postural control.NEW & NOTEWORTHY The relationship between the complexity of the center of pressure (COP) and balance performance is not fully established. The task constraints and the filtering decomposition of the COP could influence this relationship. COP complexity is related to a better balance performance only in low frequencies and midfrequencies of the COP. The different frequencies measure different postural control components. Filtering decomposition should be explored in future studies to address the underlying mechanisms of postural control.
Keywords: balance; complexity; detrended fluctuation analysis; postural control.