Bone Abstracts

Objective: The use of high-impact weight bearing physical activities has been accepted as a means to increase osteogenic effects on bone. Studies in adolescents found that physical activity could counteract the detrimental effects on bone associated with television time in boys and time spent studying in girls. Our aim was to test the effects of the percent of time spent in moderate plus vigorous activities (ModVig) and sitting (SIT) on bone health. We hypothesized that high ModVig would increase bone size and strength and offset the detrimental bone effects of high SIT.

Methods: This cross-sectional study included 159 (83 males) children aged 6–18 years (mean 9.6±2.7). Periosteal (PeriC) and endosteal (EndoC) circumference, cortical thickness (CrtThk) and bone strength (pSSI) of the distal tibia were measured using pQCT. Bone mineral content (BMC) of the hip, femoral neck (FN), spine and whole body were measured by DXA. ModVig and SIT were obtained by questionnaire. Regression analyses controlling for age, sex, age-by-sex, height and weight were used to test effects of ModVig and SIT on bone outcomes.

Results: ModVig was not associated with any DXA measures. Higher percent ModVig lead to a smaller EndoC (P=0.01) with no changes in other pQCT measures. On the other hand, children with higher SIT had smaller PeriC and EndoC, which lead to a lower pSSI than children who sat less (P≤0.02, all) despite a greater CrtThk with higher SIT (P=0.03). Children with high SIT also had lower hip BMC (P=0.01).

Conclusions: Children with higher percent of time spent sitting had smaller and weaker bones in the lower leg and had lower hip BMC than children who sat less. Time spent in moderate to vigorous activity did not offset these negative outcomes. Public health messaging aimed at decreasing sitting time in addition to increasing moderate plus vigorous activity may have more of a beneficial effect on improving pediatric bone health.

Disclosure: The authors declared no competing interests.