Only a few positive post-intervention values in fitness measures after structured and semi-structured school-based physical activity interventions

This study aimed to compare changes in 9-11 years old Italian children for fitness outcomes, following a structured multicomponent intervention, The Daily Mile, and usual school physical education lessons (i.e., control group). Before and after three different 6-month weekly PAIs (2 h of structured physical workouts, with a sport science expert; 4 units of The Daily Mile + 1 h of physical activity with the generalist teacher; control group, 2 h of physical activity with the generalist teacher), 263 children were anthropometrically measured (stature, body mass), and evaluated by means of physical tests regarding sprint (20 m-sprint), endurance (shuttle-run), balance (single-leg-stance), dominant upper-limb strength (handgrip), lower-limbs muscle power (standing-long-jump), and flexibility (sit-and-reach) physical fitness qualities. To distinguish active and non-active children, participants filled the Physical Activity Questionnaire for Older Children - Italian version (PAQ-C-it) at PRE. Post-intervention outcomes were analyzed using linear mixed-effects models (with PRE values, age and PRE-POST Delta BMI as covariates). For standing long jump, the structured PAI determined higher post-intervention values than the control group (estimated difference = 18.55 +/- 4.6 cm, p = 0.001, d = 1.03) and The Daily Mile group (estimated difference = 10.89 +/- 3.09 cm, p = 0.008, d = 0.6). For single-leg stance with eyes open, the structured PAI group achieved higher post-intervention values than The Daily Mile group (estimated difference = 25.10 +/- 8.16 s, p = 0.016, d = 0.7). No other difference emerged between PAIs. In addition, male reported better shuttle run higher post-intervention values (p = 0.008, eta p2 = 0.03) than female. No effects for sex-intervention-physical status interactions emerged. Therefore, PAI effects are limited and outcome-specific, with only structured approach able to promote some fitness enhancements, regardless from the beginning physical status of students, thus suggesting to moderately consider the association between school PAIs and substantial fitness positive post-intervention variations.