Longitudinal changes and tracking of in-school physical activity in primary school children: four-year longitudinal study

Background There is little evidence on the tracking of physical activity during school hours. In addition, tracking physical activity in schools provides important evidence for understanding children’s physical activity and conducting intervention studies. Therefore, this study examined longitudinal changes and tracking of in-school physical activity in primary school children.
Methods In this study, physical activity was investigated longitudinally in primary school children for 4 years. The baseline participants consisted of 103 second-grade students (7–8 years old) who participated. Step counts and moderate-to-vigorous physical activity (MVPA) in school and during first recess and lunch/second recess were examined using an accelerometer (Kenz Lifecorder GS 4-second version; Suzuken Co. Ltd, Nagoya, Japan).
Results After excluding missing data (moving school; n = 8, physical activity; n = 8), 87 (43 boys and 44 girls) of whom were included in the final analysis. Step counts and MVPA during school and physical education in boys did not decrease across the school years. By contrast, in girls, step counts during school did not decrease across the school years, however MVPA did decrease. In addition, for both sexes, step counts and MVPA during first recess decrease across the school years. During lunch/second recess, only step counts decrease across the school years in both sexes. In addition, the tracking coefficients for step counts and MVPA for boys in school and during first recess and lunch/second recess were found across many school years. Contrarily, girls had fewer significant tracking coefficients between school years than boys. There were also few significant tracking coefficients between grades for physical education step counts and MVPA for both boys and girls.
Conclusions Our results suggested that in-school step counts for both boys and girls does not decrease across the school years. However, given that girls demonstrated reduced levels of in-school MVPA across the school years, it is important to promote strategies to increase MVPA in this group.