Time-of-day influences on static and dynamic postural control.

CONTEXT: Assessment of postural control is used extensively in clinical and research applications. Time of day affects aspects of physical performance, but whether it also affects postural control is unknown. OBJECTIVE: To determine the influence of time of day on static and dynamic postural control. DESIGN: For each static postural control variable, a separate 3-way (day, time, eye) repeated-measures analysis of variance (ANOVA) was performed. For the dynamic postural control variable, a 2-way (day, time) repeated-measures ANOVA was performed. SETTING: University research laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty healthy college-aged subjects. INTERVENTION(S): Static and dynamic postural control of each subject was assessed in a laboratory at 10:00, 15:00, and 20:00 on 2 consecutive days. MAIN OUTCOME MEASURE(S): Unilateral static postural control was assessed with eyes open and closed on a forceplate using center-of-pressure velocity in the anterior-posterior and medial-lateral planes as the dependent variables. Dynamic postural control was assessed with the anterior reaching direction of the Star Excursion Balance Test using reach distances normalized to leg length as the dependent variable. RESULTS: For static postural control, velocity scores in both directions were lower at 10:00 than at 15:00 and 20:00 on day 1 (P < .05). For dynamic postural control, normalized reach distance was greater at 10:00 than at 15:00 and 20:00 (P < .05). CONCLUSIONS: Time of day had a consistent influence on dynamic postural control that suggests performance of this task may be better in the morning than in the afternoon or evening. The influence of time of day on static postural control was not as consistent and we feel requires further investigation. These findings have implications for researchers and clinicians when implementing and interpreting postural control testing.