Exercise and Bone Development in Young Girls

描述(由申请人提供)：骨质疏松症及其增加的骨折风险，是一个主要的公共卫生问题。虽然过去的大多数预防工作都以减缓骨丢失为目标，但人们对发育过程中骨骼对干预措施的适应非常感兴趣。骨量和结构几何形状都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，结构对机械刺激具有适应性。儿童和青少年可能比成年人更有能力改变结构几何形状，以及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，并可能在以后的生活中防止骨折。这一主张还没有得到充分的检验。此外，从为数不多的现有研究来看，关于女孩在不同发育阶段的相对适应情况，有相互矛盾的报告。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(例如，跳跃、跳跃等)”的影响。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。对4级(Tanner阶段1)和6级(Tanner阶段II和III)的女孩进行骨矿含量(BMC)、骨密度(BMD)和骨结构几何学的基线测量，并在此后定期测量，以评估两年锻炼对骨积累和结构的影响。将在干预后1年和2年进行跟踪措施，以评估干预效果是否持续。体力活动、饮食、成熟度、体型和身体成分也将被测量，以控制生长、成熟度和可能影响骨骼发育的重要环境因素的差异，以及对干预的适应的解释。这项研究在几个方面是独一无二的，包括：i)除了BMC和BMD外，它还关注结构变化；ii)它侧重于青春期前和青春期早期女孩，以确定发生适应的最佳“机会之窗”；iii)为期两年的干预，以便我们能够检查更长时间的干预是否继续增加益处；iv)对重要协变量的全面衡量；以及v)它的重点是在干预后两年的后续跟踪中保持适应。过去的研究未能充分控制身体和骨的大小，这混淆了DXA和DXA的骨密度，而且随着成熟度的变化而变化。包括pQCT vBMD和结构几何学测量，可以适当地解释BMC和BMD的变化，并提供了一种关于运动对发育中女孩结构适应的影响的前瞻性测试，这些影响有助于骨骼强度，并可能对降低骨折风险具有持久的好处。我们预计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，并将为旨在促进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选择提供关键信息。

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.