Positive effects on bone mineralisation and muscular fitness after 10 months of intense school-based physical training for children aged 8-10 years: the FIT FIRST randomised controlled trial

Objectives We investigated whether musculoskeletal fitness of school children aged 8-10 years was affected by frequent intense PE sessions. Design and participants 295 Danish school children aged 8-10 years were cluster randomised to a small-sided ball game group (SSG) (n=96, four schools, five classes), a circuit strength training group (CST) (n=83, four schools, four classes) or a control group (CON, n=116, two schools, five classes). Intervention SSG or CST was performed 3x40 min/week over 10 months. Whole-body dual-energy X-ray absorptiometry (DXA) scans were used to determine areal bone mineral density (aBMD), bone mineral content (BMC) and lean body mass (LBM). Flamingo balance, standing long jump and 20-m sprint tests were used to determine muscular fitness. Results Analysis of baseline-to-10 months change scores showed between-group differences in favour of the interventions in whole-body aBMD (SSG vs CON: 8 mg/ cm2, 95% CI 3 to 13; CST vs CON: 7 mg/ cm2, 95% CI 2 to 13, p< 0.05) and leg BMC (SSG vs CON: 11 g, 95% CI 4 to 18; CST vs CON: 11 g, 95% CI 3 to 18, p< 0.05). SSG had higher change scores in leg aBMD compared with CON and CST (SSG vs CON: 19 mg/ cm2, 95% CI 11 to 39, p< 0.05; SSG vs CST: 12 mg/ cm2, 95% CI 3 to 21, p< 0.05), and CST had higher change scores in whole-body BMC compared with CON (CST vs CON: 25 g, 95% CI 10 to 39, p< 0.05). Both training types resulted in higher change scores in postural balance (SSG vs CON: 2.4 fewer falls/ min, 95% CI 0.3 to 4.5, CST vs CON: 3.6 fewer falls/ min, 95% CI 1.3 to 5.9, p< 0.05) and jump length (SSG vs CON: 10%, 95% CI 5 to 16%; CST vs CON: 9%, 95% CI 3 to 15%, p< 0.05). No between-group differences were observed for sprint performance or LBM (p> 0.05). Conclusions In conclusion, 3x40 min/ week with SSG or CST over a full school year improves bone mineralisation and several aspects of muscular fitness of children aged 810 years, suggesting that well-organised intense physical education classes can contribute positively to develop musculoskeletal health in young children.