Exercise and Bone Development in Young Girls

描述（由申请人提供）：骨质疏松症，其骨折风险增加，是一个主要的公共卫生问题。虽然过去的大多数预防措施都是针对减缓骨质流失，但人们对发育期间骨骼对干预措施的适应性非常感兴趣。骨量和结构几何形状是骨强度和骨折风险的重要决定因素。动物研究清楚地表明了发育过程中对机械刺激的结构适应。儿童和青少年比成人更有能力改变结构几何形状，并增加骨矿物质质量和密度以应对增加的负荷，这将增加骨强度并可能在以后的生活中防止骨折。这一主张尚未得到充分检验。此外，从现有的几项研究来看，关于女孩在不同发展阶段的相对适应性，存在相互矛盾的报告。因此，干预的最佳时机尚不清楚。为了解决这些问题，我们建议评估“地面反应”的影响（例如，跳跃，跳跃等）对青春期前和青春期早期女孩骨骼宏观结构发育的影响。将在基线时和此后定期测量4级（坦纳1期）和6级（坦纳II期和III期）女孩的骨矿物质含量（BMC）、骨矿物质密度（BMD）和骨结构几何学，以评估两年运动对骨累积和结构的影响。在干预后1年和2年进行随访，以评估干预效果是否持续。还将测量身体活动、饮食、成熟、体型和身体组成，以控制可能影响骨骼发育的生长、成熟和重要环境因素的差异以及对干预适应性的解释。这项研究在以下几个方面是独一无二的，包括：i）除了BMC和BMD之外，它还关注结构变化; ii）关注青春期前和青春期早期的女孩，以确定发生适应的最佳“机会窗口”; iii）为期两年的干预，因此我们可以检查是否继续通过更长时间的干预获得益处; iv）全面测量重要的协变量;以及v）其重点是在干预后两年的后续行动中保持适应性。过去的研究未能充分控制身体和骨骼的大小，这混淆了DXA的区域BMD，并且随着成熟而变化。纳入pQCT vBMD和结构几何学测量，可以适当解释BMC和BMD的变化，并提供了一个前瞻性测试，锻炼对发育中女孩的结构适应性的影响，有助于骨强度，并可能对降低骨折风险具有持久的益处。我们希望这项研究将为我们理解骨骼宏观结构对运动的适应做出重大贡献，并将为旨在增强骨骼发育以降低未来骨折风险的干预措施的设计和最佳时机提供关键信息。

DESCRIPTION (provided by applicant): Osteoporosis, with its increased fracture risk, is a major public health concern. While the majority of past prevention efforts have targeted slowing bone loss, there is great interest in skeletal adaptations to interventions during development. Both bone mass and structural geometry are important determinants of bone strength and fracture risk. Animal studies clearly show structural adaptations to mechanical stimuli during development. Children and adolescents, more so than adults, may have the ability to modify structural geometry as well as increase bone mineral mass and density in response to increased loads, which would increase bone strength and potentially protect against fractures later in life. This proposition has not been adequately tested. Moreover, from the few available studies, there have been conflicting reports regarding relative adaptations in girls at different stages of development. Thus the optimal timing of interventions is not known. To address these issues, we propose to assess the effects of "ground-reaction (e.g., jumping, hopping, etc.) exercise on bone macro-architectural development in pre-pubescent and early pubescent girls. Bone mineral content (BMC), bone mineral density (BMD), and bone structural geometry will be measured in girls in 4th (Tanner stage 1) and 6th (Tanner stage II and III) grade at baseline, and at regular intervals thereafter, to assess the effects of two years of exercise on bone accrual and structure. Follow-up measures will be made at 1 and 2 years post intervention to assess whether intervention effects persist. Physical activity, diet, maturation, body size and body composition will also be measured to control for differences in growth, maturation, and important environmental factors that may influence bone development and the interpretation of the adaptations to the intervention. This study is unique in several ways including: i) its focus on structural changes in addition to BMC and BMD; ii) the focus on pre- and early pubescent girls to define the optimal "window of opportunity" for adaptation to occur; iii) the two-year intervention so we can examine whether benefits continue to accrue with longer duration intervention; iv) comprehensive measurement of important covariates; and v) its focus on the maintenance of adaptations over two years of follow-up after intervention. Past studies have failed to adequately control for body and bone size, which confound area) BMD from DXA, and which vary with maturation. The inclusion of pQCT vBMD and measures of structural geometry allows an appropriate interpretation of changes in BMC and BMD, and provides a prospective test of the effects of exercise on structural adaptations in developing girls which contribute to bone strength and which may have lasting benefit for lowering fracture risk. We expect this study will make a significant contribution to our understanding of bone macro-architectural adaptations to exercise and will provide critical information for the design and optimal timing of interventions designed to enhance bone development to lessen future fracture risk.