The purpose of the present investigation was to clarify the relationship between age and bout duration of physical activity (PA) under free-living conditions in female adults. Forty-three females wore an accelerometer (Lifecorder) for seven consecutive days in order to determine the time spent in PA at light intensity (LPA), at moderate intensity (MPA), and at vigorous intensity (VPA). The PA was divided according to the bout duration, such as PA lasting longer than 16 s, 32 s, 60 s, 3 min, > 5 min, and > 10 min (PA16s, PA32s, PA1m, PA3m, PA5m, PA10m). The time for LPA32s, LPA1m, MPA16s, VPA16s, and the total time for MPA and VPA were significantly associated with age (P < 0.05). There were no significant associations between age and PA lasting > 60 s, regardless of intensity category. The results of the present pilot study suggest that the age-associated differences in PA occur mainly in PA lasting 1 min or shorter duration.
