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Jpn J Biomechanics Sports Exercise 8(3):150-162, 2004

On the evaluation parameter of static posturography in view of the stationarity and reproducibility of the measurements

Kei MASANI1)2), Motoki KOUZAKI1), Hatsuki SHIRASAWA1), Shin-ya KUNO3), Hiroaki KANEHISA1), Tetsuo FUKUNAGA4)

1)Graduate School of Arts and Sciences, The University of Tokyo
2)Institute of Biomaterials and Biomedical Engineering, University of Toronto
3)Center for Tsukuba Advanced Research Alliance, University of Tsukuba
4)Department of Sports Sciences, Waseda University

Abstract

A lot of evaluation parameters of the static posturography for the age-related change of the postural stability has been presented to date. However, the time-dependent stochastic property and the dynamics of postural sway have not been adequately considered. The purpose of this study was to investigate evaluation parameters of postural stability change in the aging population considering the stationarity of variables. The participants were healthy adults(20-83 years, n=395). First, the stationarity of variables(the center of pressure(COP), the center of mass aceleration(ACC), and the differential series of COP(dCOP))and the reproducibility of summary statistics of these variables were examined using data of 80 male participants below 60 years old. Then, the age-related change of these evaluation parameters was examined using all participants' data. The results indicated that, 1)ACC and dCOP were more stationary than COP;2)the summary statistics of ACC and dCOP were highly reproducible;3)the Hurst's exponent in the short time region(HS)was highly reproducible, whereas the Hurst's exponent in the long time region(Hl)was not;4)the mean velocity(V), which was equivalent to the mean amplitude of dCOP, and the squared mean velocity(VS)of COP clearly increased accompanied with age;5)there were also increasing trends with age for statistics of ACC;6)Hl had a decreasing trend with age. We conclude that V, VS and statistics of ACC are adequate as evaluation parameters to detect age-related change of postural stability, while the summary statistics of COP are not adequate as evaluation parameters because of un-stationarity of COP. Further, while Hurst's exponents have potential as evaluation parameters, it is probably difficult to obtain accurate values in the standard measurement protocol of posturography.

Key Words: posturography, center of pressure, center of mass, age

Submittted for Publication : May 25, 2003,

Accepted for Publication : July 18, 2004

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