RESUMEN
Background: Physical activity (PA) increases bone mass, especially in late prepuberty and early puberty, but it remains unclear if and how PA affects both bone formation and bone resorption. Materials and Methods: We included 191 boys and 158 girls aged 7.7 ± 0.6 (mean ± SD) in a population-based PA intervention study. The intervention group (123 boys and 94 girls) received daily physical education (PE) in school (40 min/day; 200 min/week) from study start and during the nine compulsory school years in Sweden. The controls (68 boys and 64 girls) received the national standard of 1-2 classes PE/week (60 min/week). During the intervention, blood samples were collected at ages 9.9 ± 0.6 (n = 172; all in Tanner stages 1-2) and 14.8 ± 0.8 (n = 146; all in Tanner stages 3-5) and after termination of the intervention at age 18.8 ± 0.3 (n = 93; all in Tanner stage 5) and 23.5 ± 0.7 (n = 152). In serum, we analyzed bone formation markers [bone-specific alkaline phosphatase (bALP), osteocalcin (OC), and N-terminal propeptide of collagen type 1 (PINP)] and bone resorption markers [C-terminal telopeptide cross links (CTX) and tartrate-resistant acid phosphatase (TRAcP 5b)]. Linear regression was used to compare age and sex-adjusted mean differences between intervention children and controls in these markers. Results: Two years after the intervention was initiated (at Tanner stages 1-2), we found higher serum levels of bALP and OC, and lower serum levels of TRAcP 5b in the intervention compared with the control group. The mean difference (95% CI) was for bALP: 13.7 (2.1, 25.3) µg/L, OC: 9.1 (0.1, 18.1) µg/L, and TRAcP 5b: -2.3 (-3.9, -0.7) U/L. At Tanner stages 3-5 and after the intervention was terminated, bone turnover markers were similar in the intervention and the control children. Conclusion: Daily school PA in the late prepubertal and early pubertal periods is associated with higher bone formation and lower bone resorption than school PA 1-2 times/week. In late pubertal and postpubertal periods, bone formation and resorption were similar. Termination of the intervention is not associated with adverse bone turnover, indicating that PA-induced bone mass benefits gained during growth may remain in adulthood.
RESUMEN
Daily school physical activity (PA) improves musculoskeletal traits. Whether or not benefits remain in adulthood is debated. We included in this study 131 children that took part in an intervention with 40 minutes of PA per school day (200 minutes per week) from age 6 to 9 years (grade one) to age 14 to 16 years (grade nine), whereas 78 children continued with national recommended school physical education of 60 minutes per week. Measurements were done with dual-energy X-ray absorptiometry (bone mineral content [BMC], bone mineral density [BMD], and bone area), and a computerized knee dynamometer (peak torque muscle strength) at study start, at the end of the intervention, and 7 years after the intervention. Group differences from study start and end of the intervention to 7 years thereafter were estimated by analyses of covariance (adjusted for sex and follow-up time). Musculoskeletal gains from study start to 7 years after termination of the intervention were higher in the intervention group (total body less head BMC +182.5 g [95% confidence interval {CI}, 55.1-309.9] and BMD +0.03 g/cm2 [95% CI, 0.003-0.05], femoral neck area + 0.2 cm2 [95% CI, 0.1-0.4], and knee flexion peak torque muscle strength at 60 degrees per second +9.2 Nm [95% CI, 2.9-15.5]). There was no attenuation during the 7 years that followed termination of the intervention (all group comparisons p > 0.05). Benefits in musculoskeletal gains remain 7 years after termination of a daily school-based PA program, without attenuation after termination of the program. Daily school PA may counteract low bone mass and inferior muscle strength in adulthood. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.