Objective assessment of school-time physical activity of a grade 1-2 junior school students in Beijing

Objective: To quantify the physical activity (PA) level during school time, especially in PE class, among Beijing junior school students.

Methods: 81 healthy adolescents (37 boys and 44 girls) aged 11-15 were recruited from grade 1-2 of a junior school, and a hip-worn ActiGraph GT3X + accelerometer was used to measure students' PA. Accelerometer-determined steps, moderate-and vigorous-intensity PA (MVPA), vigorous-intensity PA (VPA) and MET-mins at school time and physical education (PE) class were assessed.

Results: During school time, girls spent (47.2 +/- 16.0) mins performing, and boys (67.3 +/- 20.5) mins per day (P < 0.01). Boys also had more steps per day, VPA time and MVPA MET-min than girls (P < 0.001). In PE class, boys spent 53.6% +/- 10.2% of time in MVPA, as compared to girls' 35.2% +/- 7.2%. Boys with normal BMI had the highest VPA time during PE than other groups (P < 0.05). No significant BMI group differences in PA level were found in girls.

Conclusions: PA in school time was objectively qualified in Beijing junior school students. Girls were less active than boys. PE class provided a major portion of the VPA time and MVPA MET-min in school time PA for boys and girls. Boys with normal BMI had the highest PA level during PE classes.