ABSTRACT
Maintaining posture and movement stabilities, that is, balance, is particularly important for safety in daily life along with performing exercises. The purpose of this study was to clarify the changes in static and dynamic balance abilities from 8:00 to 18:00 and investigate the factors of change in balance ability among healthy young people. The subjects were nine relatively active healthy university students. The static and dynamic balance abilities were measured by a body sway test while static standing and the Cross Test, in which the center of gravity was voluntarily moved to the maximum in the front, back, left, and right directions, respectively. No change with time was observed in the static balance index. However, the maximum amplitude in the anteroposterior direction, an index of dynamic balance, significantly increased with time (8:00 vs 18:00, p<0.05). Sleepiness score significantly decreased with time (8:00 vs 18:00, p<0.05). As a result of simple correlation analysis, there were significant relationships between static balance indices (environmental area and rectangle area) and autonomic activity index (heart rate variability) at many times (p<0.05). Thus, it was concluded that the static balance ability was not affected by time. Furthermore, the ability to move the center of gravity in the anteroposterior direction of dynamic balance was low during morning and increased with time in relatively active healthy young people. Additionally, it was suggested that autonomic nervous activity was associated with static balance and the sleepiness was associated with dynamic balance.