The Static Standing Postural Stability Measured by Average Entropy

Abstract

Static standing postural stability has been measured by multiscale entropy (MSE), which is used to measure complexity. In this study, we used the average entropy (AE) to measure the static standing postural stability, as AE is a good measure of disorder. The center of pressure (COP) trajectories were collected from 11 subjects under four kinds of balance situation, from stable to unstable: bipedal with open eyes, bipedal with closed eyes, unipedal with open eyes, and unipedal with closed eyes. The AE, entropy of entropy (EoE), and MSE methods were used to analyze these COP data, and EoE was found to be a good measure of complexity. The AE of the 11 subjects sequentially increased by 100%as the balance situations progressed from stable to unstable, but the results of EoE and MSE did not follow this trend. Therefore, AE, rather than EoE or MSE, is a good measure of static standing postural stability. Furthermore, the comparison of EoE and AE plots exhibited an inverted U curve, which is another example of a complexity versus disorder inverted U curve.

Complexity and Disorder of 1/fα Noises

“…It is widely considered that the complexity is relatively high for a complex system intermediate between extreme order and disorder. This results in an inverted U relation between the complexity and the disorder for complex physiologic signals or complex simulated 1/ noises [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Exploring the resemblance between the two kinds of signals would provide the underlying mechanism of the physiologic signals of health and disease [ 10 , 11 , 12 , 13 , 14 ].…”

“…AE is used to differentiate the three groups of subjects, namely congestive heart failure (CHF), atrial fibrillation (AF), and healthy groups [ 8 ]. Furthermore, the expected inverted U curves of EoE vs. AE have been realized for real physiological signals such as heart rate signals and static standing postural stability [ 7 , 8 , 9 ].…”