title: Universal and individual characteristics of postural sway during quiet standing in healthy young adults.
abstract: The time course of the center of pressure (CoP) during human quiet standing, corresponding to body sway, is a stochastic process, influenced by a variety of features of the underlying neuro-musculo-skeletal system, such as postural stability and flexibility. Due to complexity of the process, sway patterns have been characterized in an empirical way by a number of indices, such as sway size and mean sway velocity. Here, we describe a statistical approach with the aim of estimating "universal" indices, namely parameters that are independent of individual body characteristics and thus are not "hidden" by the presence of individual, daily, and circadian variations of sway; in this manner it is possible to characterize the common aspects of sway dynamics across healthy young adults, in the assumption that they might reflect underlying neural control during quiet standing. Such universal indices are identified by analyzing intra and inter-subject variability of various indices, after sorting out individual-specific indices that contribute to individual discriminations. It is shown that the universal indices characterize mainly slow components of sway, such as scaling exponents of power-law behavior at a low-frequency regime. On the other hand, most of the individual-specific indices contributing to the individual discriminations exhibit significant correlation with body parameters, and they can be associated with fast oscillatory components of sway. These results are consistent with a mechanistic hypothesis claiming that the slow and the fast components of sway are associated, respectively, with neural control and biomechanics, supporting our assumption that the universal characteristics of postural sway might represent neural control strategies during quiet standing.
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Department of Statistics, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Smith
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Kiyono
authors.affiliation: Department of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Tanahashi
authors.affiliation: Department of Neurology, Toneyama National Hospital, Osaka, Japan.
authors.forename: Saburo
authors.initials: S
authors.lastname: Sakoda
authors.affiliation: RBCS Department, Fondazione Istituto Italiano di Tecnologia, Genoa, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Morasso
authors.affiliation: Graduate School of Engineering Science, Osaka University, Toyonaka, Japan taishin@bpe.es.osaka-u.ac.jp.
authors.forename: Taishin
authors.identifier: http://orcid.org/0000-0002-6545-2097
authors.initials: T
authors.lastname: Nomura
keywords: Intermittent control; postural control; postural sway; slow component