Bone strength accrual across adolescent growth and the influences of physical activity and sedentary time

• Main Author: Gabel, Leigh Elizabeth Christine
• Language: English
• Published: University of British Columbia 2017
• Online Access: http://hdl.handle.net/2429/61281

With recent advances in imaging technologies, we are acquiring a better understanding of the complex hierarchy of bone and how bone adapts its geometry, microarchitecture and ultimately, its strength to withstand the loads imposed upon it during adolescent growth. Thus, in this thesis, I examine the influence of physical activity (PA), sedentary time, maturity and sex on estimated bone strength and its determinants (i.e., microarchitecture, geometry and density) across adolescence. This thesis is based on the UBC Healthy Bones III Study (HBSIII), a mixed longitudinal cohort of healthy girls and boys age 8-12 years at study entry. We assessed bone strength, geometry and density at the tibial shaft using peripheral quantitative computed tomography (pQCT) and bone strength, microarchitecture, geometry and density at the distal tibia and radius using high-resolution pQCT (HR-pQCT). We assessed PA and sedentary time using accelerometry. Four studies comprise this thesis. First, I investigated cross-sectional associations between sedentary time and bone strength and its determinants at the distal tibia by HR-pQCT. I found no associations between sedentary time and bone parameters. Second, I examined maturity- and sex-related adaptations of bone geometry and strength at the tibial shaft using pQCT. I found that larger bone area in boys provided them a greater bone strength advantage compared with girls across adolescence. Third, I examined maturity- and sex-related adaptations of bone strength and its determinants by HR-pQCT at the distal tibia and radius. I found greater bone strength in boys across adolescence was underpinned by greater trabecular bone volume and total bone area. Fourth, I examined prospective associations between PA, sedentary time and bone strength and its determinants at the distal tibia and radius using HR-pQCT. I observed greater bone strength and trabecular bone volume in participants engaging in more PA and lower total bone area in participants engaging in more sedentary time. Collectively, these studies enhance our understanding of how bone is gained during adolescence and add a unique perspective to the benefits of PA for bone strength and its determinants. === Medicine, Faculty of === Experimental Medicine, Division of === Medicine, Department of === Graduate