title: Invariant density analysis: modeling and analysis of the postural control system using Markov chains.
abstract: In this paper, a novel analysis technique, invariant density analysis (IDA), is introduced. IDA quantifies steady-state behavior of the postural control system using center of pressure (COP) data collected during quiet standing. IDA relies on the analysis of a reduced-order finite Markov model to characterize stochastic behavior observed during postural sway. Five IDA parameters characterize the model and offer physiological insight into the long-term dynamical behavior of the postural control system. Two studies were performed to demonstrate the efficacy of IDA. Study 1 showed that multiple short trials can be concatenated to create a dataset suitable for IDA. Study 2 demonstrated that IDA was effective at distinguishing age-related differences in postural control behavior between young, middle-aged, and older adults. These results suggest that the postural control system of young adults converges more quickly to their steady-state behavior while maintaining COP nearer an overall centroid than either the middle-aged or older adults. Additionally, larger entropy values for older adults indicate that their COP follows a more stochastic path, while smaller entropy values for young adults indicate a more deterministic path. These results illustrate the potential of IDA as a quantitative tool for the assessment of the quiet-standing postural control system.
authors.affiliation: Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. hur@uwm.edu
authors.forename: Pilwon
authors.initials: P
authors.lastname: Hur
authors.forename: K Alex
authors.initials: KA
authors.lastname: Shorter
authors.forename: Prashant G
authors.initials: PG
authors.lastname: Mehta
authors.forename: Elizabeth T
authors.initials: ET
authors.lastname: Hsiao-Wecksler
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D003198:Computer Simulation; D025461:Feedback, Physiological / Q000502:physiology; D005260:Female; D005528:Foot / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015233:Models, Statistical; D004856:Postural Balance / Q000502:physiology*; D011312:Pressure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult