Purpose: Most pediatric physical activity and bone health research has focused on the period immediately around puberty; few have addressed bone structural strength outcomes. This study assessed the magnitude and consistency of the longitudinal relationships between device-measured vigorous-intensity physical activity (VPA) and structural bone strength outcomes across adolescence to emerging adulthood. Methods: Participants with 3 to 5 bone scans between the age of 11 and 19 years were studied (N = 439, 220 females, 1838 records). Dual-energy X-ray absorptiometry scans of the hip (hip structural analysis) and peripheral quantitative computed tomography scans of the tibia were obtained. Outcomes included femoral neck section modulus, femoral neck cross-sectional area, tibial Bone Strength Index, and tibial torsion strength (polar Strength Strain Index). Sex-specific bone mixed growth models were developed using biological age (chronological age − age at peak height velocity) as the time variable, and height, weight, and device-measured VPA as time-varying covariates. Models also included the VPA–biological age interaction. Results: Individual-centered VPA and the VPA–biological age interaction were significantly, positively associated (P < .05) with Bone Strength Index, polar Strength Strain Index, section modulus, and cross-sectional area in males and females, indicating accumulative effects of VPA throughout maturation and beyond. Conclusion: Bone remains responsive to the mechanical loading of physical activity throughout adolescence and into emerging adulthood. Attention should be placed on promoting bone-strengthening physical activity after the prepubertal years when adult exercise patterns are likely formed.
Kristen M. Metcalf, Elena M. Letuchy, Steven M. Levy and Kathleen F. Janz
Joanna L. Morrissey, Phyllis J. Wenthe, Elena M. Letuchy, Steven M. Levy and Kathleen F. Janz
In a sample of 291 adolescents (mean age 13 yr), seven psychosocial factors, including family support, were examined in relation to accelerometry-derived physical activity (PA) measured after school and during the weekend. Gender-specific stepwise linear regression analyses determined which combinations of factors explained the variance in nonschool moderate to vigorous PA and nonschool total PA after adjusting for % BF, age, and maturity (p ≤ 0.05). Being praised by a family member and % BF explained 13% of the variance in female nonschool MVPA, while being praised and maturity explained 13% of the variance in nonschool total PA. Having a family member watch him participate, % BF, and age explained 11.5% of the variance in male nonschool MVPA, while having a family member participate with him explained 6.4% of the variance in nonschool total PA. Despite adolescents’ growing independence, family support continues to influence PA levels.