title: Feet distance and static postural balance: implication on the role of natural stance.
abstract: The purpose of this study was to investigate 1) the effect of feet distance on static postural balance and 2) the location of natural feet distance and its possible role in the relationship of feet distance and postural balance. Static balance tests were performed on a force platform for 100 s with six different feet distances (0, 5, 10, 15, 20, 25 cm). Measures of postural balance included mean amplitude of horizontal ground reaction force (GRF) as well as the mean distance and velocity of the center of pressure (COP). All measures were discomposed into anterioposterior and mediolateral directions. ANOVA and post-hoc comparison were performed for all measures with feet distance as an independent factor. Also measured was the feet distance at the natural stance preferred by each subject. All measures significantly varied with feet distance (p<0.001). Mean distance of COP showed monotonic decrease with feet distance. Mean amplitude of horizontal GRF as well as mean velocity of COP showed U-shaped pattern (decrease followed by increase) with the minimum at the feet distance of 15 cm or 20 cm, near which the natural feet distance of 16.5 (SD 3.8) cm was located. COP is regarded to be an approximation of the center of mass (hence the resultant performance of postural control) in an inverted pendulum model with the horizontal GRF ignored. On the other hand, horizontal GRF is the direct cause of horizontal acceleration of a center of mass. The present result on horizontal GRF shows that the effort of postural control is minimized around the feet distance of natural standing and implies why the natural stance is preferred.
authors.affiliation: The School of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea.
authors.forename: Ji-Won
authors.initials: JW
authors.lastname: Kim
authors.affiliation: The School of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Kwon
authors.affiliation: The School of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea.
authors.forename: Hyung-Min
authors.initials: HM
authors.lastname: Jeon
authors.affiliation: The School of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea.
authors.forename: Min-Jung
authors.initials: MJ
authors.lastname: Bang
authors.affiliation: The School of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea Research Institute of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea.
authors.forename: Jae-Hoon
authors.initials: JH
authors.lastname: Jun
authors.affiliation: The School of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea Research Institute of Biomedical Engineering, Konkuk University, Chungnju, 380-701, Korea.
authors.forename: Gwang-Moon
authors.initials: GM
authors.lastname: Eom
authors.affiliation: Department of Mechanical Engineering, Sejong University, Seoul, 143-747, Korea.
authors.forename: Do-Hyung
authors.initials: DH
authors.lastname: Lim
mesh_terms: D000054:Acceleration; D000328:Adult; D005260:Female; D005528:Foot / Q000502:physiology*; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011312:Pressure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013647:Task Performance and Analysis
keywords: Stance width; center of pressure; ground reaction force; postural stability; preferred stance