Physical activity levels are associated with regional bone mineral density in boys.

: Youth is a crucial period for bone gain, and physical activity (PA) has shown to increase bone mineral density (BMD) in this period. However, whether PA affects regional BMD is unclear. Thus, the aim of this study was to analyze the relationship between PA levels and regional BMD in youths. Methods: The sample included 110 children and adolescents aged 6-14 years. Body mass, height, sitting trunk length, and leg length were obtained for body mass index and maturity offset calculation. The arms, pelvis, spine, trunk, and legs BMD were measured by double energy X-ray absorptiometry. The PA was evaluated by questionnaire, and youths were classified as low, moderately, or highly physically active. : The sample included 63.7% boys and 36.3% girls with mean age of sample 9.5 (±1.6) yrs. Age, body mass index, and maturity offset were similar between sexes (p > 0.05). Boys with low PA levels had lower BMD Z-score for arms (-0.20 ± 0.71 vs. 0.30 ± 1.19, p = 0.006) and legs (-0.14 ± 1.00 vs. 0.35 ± 1.06, p = 0.026) compared to highly physically active youths. Multiple linear regression showed a positive linear relationship between legs BMD and PA in boys (β = 0.72 [95% CI = 0.09; 1.36]). : In boys, low PA levels are associated with lower BMD in arms and legs.