This study was conducted to elucidate the characteristics of children who were born later in the school year, exhibiting better physical fitness. The subjects were 1202 public elementary school children (grades 1-6) in Ibaraki prefecture, for whom birth date, height, weight, physical fitness test scores, and physical activity had been assessed by questionnaire. They were divided into four categories by birth date：Q1, April-June；Q2, July-September；Q3, October-December；and Q4, January-March (including April first). All data were integrated after classification by grade and gender. Physical fitness groups were defined to include subjects who had more than 50 physical fitness deviation score as a higher physical fitness group (HPF). The others were a lower physical fitness group (LPF). Results of statistical analysis show for Q4 that physical activity of HPF had a higher value than LPF, although no difference was found for height or BMI. For HPF, a lower value was found for height of Q4 than for either Q1 or Q2, although no difference was found for BMI or physical activity. These results demonstrate that although elementary school children who were born later in the school year and who had higher physical fitness showed poor body size, they attained higher physical fitness through higher levels of physical activity.
