Influences of Soft Tissue Composition and Physical Activity on Bone Volumetric Density, Bone Geometry, and Fracture Prevalence in Young Girls
AuthorFarr, Joshua Nicholas
AdvisorGoing, Scott B.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractFractures are a major public health concern and there is an urgent need to identify high-risk individuals. This study used novel approaches in bone imaging to characterize optimal skeletal development in girls and enhance our understanding of the structural and functional deficits that contribute to skeletal fragility and fracture risk during growth. The findings indicate that fracture in girls is associated with lower trabecular bone density, but not bone macro-architecture at metaphyseal regions of weight-bearing bones, which is consistent with findings reported in children at the distal radius. These findings suggest that lower trabecular density at metaphyseal regions of long bones track throughout the appendicular skeleton and may be an early marker of skeletal fragility.Obese children are overrepresented in childhood fracture cases. Nevertheless, the effects of fat on bone during growth remain unclear. This study showed that skeletal muscle was a stronger determinant of bone parameters in girls than total body adiposity, although fat mass had a persistent, albeit weak association with bone parameters. Furthermore, fatty infiltration of skeletal muscle, which is associated with type 2 diabetes mellitus, was inversely associated with bone strength in girls. These findings are consistent with the proposed functional model of bone development which posits that forces from muscle contractions are the main mechanical challenges to which bones adapt.Physical activity during growth is critical for optimal bone development. The findings from this study support this premise and suggest that regular physical activity enhances bone strength in girls. Nevertheless, for exercise to be accepted as an important public health osteoporosis prevention strategy, lasting adaptations must be shown. Plausible biological explanations have been offered in support of the peri-pubertal years as a "window of opportunity" for maximizing the response to exercise. Findings from this study suggest that a two year school-based high-impact jumping intervention was not an effective means to enhance bone parameters in girls. Controlled dose-response trials will be necessary to test questions regarding the types, bouts, and durations of exercise required to define the "dose" of exercise needed to elicit meaningful skeletal adaptations during growth.
Degree ProgramGraduate College