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Increased school-based exercise associated with bone strength, mass in girls

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September 8, 2016

Swedish girls who participated in 200 minutes of weekly school-based physical education exhibited increased tibia cortical thickness and bone strength vs. girls who continued with the standard 60 minutes per week, according to results of a 7-year study.

“Findings of previous studies have shown that increased physical activity is associated with greater bone mass and strength in adolescents,” Jesper Fritz, MD, PhD, of Lund University and Skåne University Hospital in Malm, Sweden, said in a press release. “The findings of this study specifically underline the benefits of increasing the amount of time dedicated to school physical education classes, particularly for girls, during the important stage of bone development around adolescence. Importantly, optimizing bone mass and strength in youth has a positive impact on bone health and fracture prevention in adulthood.”

Fritz and colleagues analyzed data from students aged 6 to 9 years attending four government-funded elementary schools within the same geographic area and with a similar socioeconomic and ethnic structure as part of the Malm pediatric osteoporosis prevention study, a prospective, controlled physical activity intervention. Students in the intervention school (n = 170; 72 girls) completed 200 minutes of weekly physical education, administered in a 40-minute lesson daily for 7 years. Students in the three control schools (n = 91; 44 girls) continued with the standard 60 minutes of weekly physical education. All classes were conducted by usual physical education teachers according to regular curriculum; there were no extra classes during weekends or holidays. All children completed questionnaires to evaluate lifestyle factors; a school nurse assessed pubertal maturation according to Tanner stage at baseline. Researchers assessed tibial total and cortical area, cortical density, polar stress-strain index (SSI) and bone mass via peripheral quantitative CT after 7 years.

After adjustment, girls had 6.9% greater SSI at the 66% tibia site and between 7.7% and 11.7% greater mineral mass across various sectors at each site, as well as 0.7% increased pericortical volumetric bone mineral density at the 66% tibia site vs. girls in control schools. Results persisted after further adjustment for age at baseline and Tanner stage, weight and tibial length at follow-up, although benefits of intervention at the anterior-medial sector (P = .06) and medial sector at the 38% tibial site (P = .12) were no longer significant. Researchers did not observe any intervention effects at the 14% tibia site in girls.

“In our study, we did not observe any region-specific cortical bone adaptations more distally (14% tibia), which may be explained by the fact that this site experiences predominantly compressive loads (strains), which may be more uniformly distributed throughout the cortex, and thus less likely to stimulate localized bone (periosteal) adaptations,” the researchers wrote.

Researchers did not observe any between-group differences for boys at any of the sites. – by Regina Schaffer

Disclosure: The researchers report no relevant financial disclosures.