title: Time-of-day influences postural balance in older adults.
abstract: BACKGROUND
  Postural balance assessments are performed in both clinical and basic research settings on a daily basis. During a 24-h time span our physiology and physical performance undergo radical changes as we are influenced by the circadian rhythm. The time-of-day interaction on postural balance is unknown in older adults. The aim of this study was to investigate the time-of-day effect on postural balance in older adults.
  
  
  METHODS
  Center of pressure (CoP) excursion was measured (100 Hz) by force plate analysis in 34 older adults during 30 s of narrow quiet bilateral stance. Measurements were performed around 9a.m., 12.30 p.m. and 4 p.m. on the same day. Postural balance was quantified by velocity-moment, confidence ellipse area, total sway area and total sway length.
  
  
  RESULTS
  An overall significant time-of-day (between 9 a.m. and 4 p.m.) effect was observed for velocity-moment (mm(2)/s) 57 ± 27-65 ± 29 (p = 0.001), confidence ellipse area (mm(2)) 36 ± 16-44 ± 19 (p < 0.001), total sway area (mm(2)) 548 ± 263-627 ± 285 (p = 0.001) and total sway length (mm) 373 ± 120-379 ± 113 (p = 0.037). The variation of postural balance was mostly pronounced from midday (12.30 p.m.) toward the afternoon (4 p.m.) in all sway parameters. Specifically between 12.30 p.m. and 4 p.m. confidence ellipse area increased by 18.5%, total sway area by 17.1%, velocity-moment by 15.8% and total sway length by 4.6%. No differences were observed between 9 a.m. and 12.30 p.m. in any of the sway parameters.
  
  
  CONCLUSIONS
  This study demonstrates that time-of-day influences postural balance in older adults. These findings have important scientific and clinical relevance, as they imply that time-of-day should be a controlled factor when assessing postural balance in older adults.
authors.affiliation: Department of Geriatrics, Aalborg Hospital - Aarhus University Hospital, Denmark. martin.joergensen@rn.dk
authors.forename: M G
authors.initials: MG
authors.lastname: Jorgensen
authors.forename: M S
authors.initials: MS
authors.lastname: Rathleff
authors.forename: U
authors.initials: U
authors.lastname: Laessoe
authors.forename: P
authors.initials: P
authors.lastname: Caserotti
authors.forename: O B F
authors.initials: OB
authors.lastname: Nielsen
authors.forename: P
authors.initials: P
authors.lastname: Aagaard
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002940:Circadian Rhythm / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D005684:Gait / Q000502:physiology*; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans; D008297:Male; D008606:Mental Processes / Q000502:physiology*; D008991:Monitoring, Physiologic / Q000295:instrumentation; D004856:Postural Balance / Q000502:physiology*; D018570:Risk Assessment; D012680:Sensitivity and Specificity