Impact of a school based flag football intervention on fitness outcomes in Chinese children aged 9 to 11 years: a randomized controlled trial

To evaluate the effects of a 10-week school-based flag football programme on fitness outcomes in Chinese children aged 9 to 11 years. A two-arm, parallel-group randomized controlled trial was conducted in a public primary school in Shanghai, China. Children ( n = 147) were randomized to either flag football ( n = 74; mean age, 9.7 ± 0.5 years; 30 girls) or usual physical education (PE; n = 73; mean age, 9.7 ± 0.5 years; 32 girls). The intervention comprised 60-min sessions, delivered twice weekly for 10 weeks. Outcomes were assessed at baseline and post-intervention: the 20 m shuttle run test (laps), estimated maximal oxygen uptake (VO₂max), the 1-min jump rope test (turns), and the 50 m dash (seconds). Primary analyses followed the intention-to-treat principle using multiple imputation and repeated-measures models; subgroup analyses were conducted by sex and baseline weight status. Session intensity was monitored through heart rate (HR) in a subsample. Post-intervention data were available for 128 children (87.1%). Compared with usual physical education, the flag football group showed greater improvements in 1-min jump rope performance (between-group difference in change = 7.4 turns; p = 0.03) and 50 m dash time (between-group difference in change = -0.3 s; p = 0.013). No between-group differences in change were observed for 20 m shuttle run performance (0.7 laps; p = 0.32) or estimated VO 2 max (0.19 mL·kg −1 ·min −1 ; p = 0.37). Subgroup analyses revealed the most significant effects in boys with normal weight for estimated VO 2 max and 20 m shuttle run, boys across BMI status groups for sprint performance, and girls across BMI status groups for jump rope. A PE-embedded flag football programme effectively improved sprint speed and 1-min jump rope performance. The observed sex- and weight-specific responses suggest the need for differentiated task progression in school-based interventions to maximize fitness benefits. Trial registration: ISRCTN registry (Current Controlled Trials), ISRCTN62093106; registered 04 February 2026 (retrospectively registered).