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。虽然过去大多数预防措施的目标是减缓骨质流失，但在发育过程中骨骼适应干预措施的兴趣很大。骨量和结构几何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，在发育过程中结构适应机械刺激。与成年人相比，儿童和青少年可能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，这将增加骨骼强度，并有可能在以后的生活中防止骨折。这一主张尚未得到充分的检验。此外，从现有的少数研究来看，关于女孩在不同发育阶段的相对适应情况，存在相互矛盾的报告。因此，干预的最佳时机是未知的。为了解决这些问题，我们建议评估“地面反应”（如跳跃、跳跃等）运动对青春期前和青春期早期女孩骨骼宏观结构发育的影响。在4年级（Tanner阶段1）和6年级（Tanner阶段II和III）的女孩中，在基线和之后定期测量骨矿物质含量（BMC）、骨矿物质密度（BMD）和骨结构几何形状，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，以控制生长、成熟和可能影响骨骼发育的重要环境因素的差异，并解释对干预的适应。这项研究在几个方面是独特的，包括：i)除了BMC和BMD外，它还关注结构变化；Ii)重点关注青春期前和早期女孩，以确定适应发生的最佳“机会之窗”；Iii)为期两年的干预，这样我们就可以检查更长时间的干预是否会继续产生益处；Iv)重要协变量的综合测量；5)其重点是在干预后的两年随访中维持适应性。过去的研究未能充分控制身体和骨骼的大小，这混淆了区域骨密度和DXA，并且随着成熟而变化。包括pQCT vBMD和结构几何测量，可以适当地解释BMC和BMD的变化，并为运动对发育中的女孩结构适应的影响提供前瞻性测试，这有助于骨骼强度，并可能对降低骨折风险具有持久的益处。我们期望这项研究将对我们理解骨骼宏观结构对运动的适应性做出重大贡献，并为设计和优化干预措施提供关键信息，旨在促进骨骼发育，以减少未来的骨折风险。

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.