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 9 a.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.
An overall significant time-of-day (between 9 a.m. and 4 p.m.) effect was observed for velocity-moment (mm2/s) 57 卤 27-65 卤 29 (p = 0.001), confidence ellipse area (mm2) 36 卤 16-44 卤 19 (p < 0.001), total sway area (mm2) 548 卤 263-627 卤 285 (p = 0.001) and total sway length (mm) 373 卤 120-379 卤 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.
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.