Intersectional Effects of the FIT FIRST 10 School-Based Intervention Across Sex and Parental Country of Birth on Physical and Psychosocial Health in Danish Primary Schools.

BACKGROUND: Children with a migration background often show poorer health profiles than majority peers. Schools provide an important setting for equitable physical activity promotion. FIT FIRST 10 (FF10) delivers high-intensity, inclusive multisport activities in Danish primary schools. OBJECTIVES: To examine whether FF10 effects on physical and psychosocial outcomes differed across intersections of sex and parental country of birth (0 or 1 Danish-origin parent [0-1DOP] vs 2 Danish-origin parents [2DOP]), hypothesizing greater benefits among girls with 0-1DOP. METHODS: This subgroup analysis included 1175 children aged 7-11 years from 27 schools. 1050 had information on sex and parental country of birth (control: n = 413, FF10: n = 637). The analytical sample for the primary outcome (cardiorespiratory fitness) comprised 798 children with complete data for all variables included in the adjusted model. RESULTS: FF10 did not improve the primary outcome in any subgroup (all P ≥ .310), and no between-subgroup differences were observed. Within-subgroup effects showed reductions in fat mass, fat mass index, body mass index, and resting heart rate among boys with 2DOP (all P ≤ .026) and improved psychological well-being among girls with 0-1DOP (P = .024). Between-subgroup contrasts favored boys with 2DOP over boys with 0-1DOP for cardiometabolic outcomes and girls with 0-1DOP over girls with 2DOP for psychological well-being. Small within-subgroup declines were observed in self-reported flexibility (girls with 2DOP) and physical condition (boys with 0-1DOP). CONCLUSION: Inclusive multisport programs in Danish primary schools may enhance psychological well-being among girls with 0-1DOP, but uneven physiological effects highlight the need to optimize implementation to achieve equitable benefits.