[Purpose] We attempted to determine whether static and dynamic postural control ability fluctuated depending on the influence of the time of day (9 am, 1 pm, and 5 pm), and at which time point postural balance performance was best in healthy individuals. [Subjects and Methods] Twenty-four healthy subjects participated in this study. The static and dynamic postural balance test was conducted during three sessions (i.e., at 9 am, 1 pm, and 5 pm) with a counterbalanced order for prevention of learning effects. As outcome measurements, AP distance, ML distance, and velocity moment were adopted in the static balance test, and the performance time and total distance were measured in the dynamic balance test. [Results] For the static postural balance test, COP distance was shorter and COP velocity was slower at 9 am compared with those at 1 and 5 pm. In particular, the COP distance at 9 am was statistically different from that at 13 pm. During the dynamic postural balance test, performance time and total distance were influenced by the time of day, as the best performance was observed in the morning. [Conclusion] This study found that static and dynamic postural balance abilities were greatest in the morning and worst at 1 pm. Understanding of the mechanism of the time-of-day effect on postural balance will be helpful for assessment and treatment of postural balance by physical therapists and in making desirable clinical decisions.
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