The aim of this study was to examine the duration of physical activity (PA) bouts in prepubertal children with high-frequency accelerometry monitoring. Thirteen boys and thirteen girls (aged 8-10 years) from one school in North of France had their PA recorded during 7 days using a uniaxial Actigraph accelerometer. To examine PA behavior patterns, the epoch was set at 2 s. Times spent in light (LPA), moderate (MPA), vigorous (VPA) and very high (VHPA) intensity activity and the daily number of PA bouts of different durations (from 2 to 1200 s) were calculated for each intensity level. Data were collected in 2004. The mean duration of PA bouts was 70.8+/-13.2 s for LPA, 9.0+/-2.8 s for MPA, 4.7+/-1.2 s for VPA and 3.9+/-1.6 s for VHPA. For the whole population, 80% of MPA, 93% of VPA and 96% of VHPA lasted less than 10 s. Although times spent in VPA and VHPA represented 2.4% of the total PA time, VPA and VHPA bouts accounted for 36.1+/-5.8% of the total amount of PA. Children's PA pattern is highly transitory and intermittent whatever its intensity. Physical activity assessed with a sampling interval related to children's behavior may improve our understanding of their PA patterns.