Factors affecting the osteogenic exercise threshold

我们对驱动人类获得骨矿物质的机制的了解仍然有限。尽管我们和其他人已经证明，骨骼在生长过程中对运动特别敏感，过度训练与骨骼完整性受损有关，但相对于骨骼来说，有益的体力活动发展到过度运动的门槛还知之甚少。我们研究计划的长期目标是考察不同类型、强度和持续时间的运动对儿童、青少年和青壮年骨骼发育和适应性反应(S)所涉及的时间进程和机制(S)的影响。我们假设：a)存在一个年龄/成熟度和性别相关的运动强度和持续时间的最佳范围，以及饮食(能量)摄入量的水平，有利于骨形成和骨吸收之间的平衡，导致正向骨适应；以及b)存在成骨运动阈值，在该阈值下，过度运动有利于骨吸收，导致负的骨适应，并取决于性别和骨骼成熟度，并受膳食能量供应的影响。我们将通过反映骨骼代谢状态变化的生化(血液)标记物来监测骨骼反应，从而能够调查运动对骨骼的急性影响。特别令人感兴趣的是包括硬化素在内的骨转换的非传统标志物，以及骨保护素(OPG)和核因子B受体激活剂配体(RANKL)的比率。*该方法包括分两个阶段进行的一系列人体研究。第一阶段是一系列运动试验，将检验不同运动方案(低影响与高影响)对儿童、青少年和年轻人骨转换的急性生化反应的差异，无论男女。我们实验室将在运动前、运动后5分钟、1小时和24小时采集血样，并分析骨形成和骨吸收标记物，包括硬化素和OPG/RANKL，以及其他全身激素和炎症因子。第二阶段包括一系列运动试验，将检查骨转换标志物的变化，重点是硬化素和OPG/RANKL比率，对中度和过度运动(高和低影响)的反应，男孩和女孩，年轻男性和女性。我们将控制年轻男性和女性的饮食摄入量(卡路里限制和常规饮食)，以潜在地确定饮食摄入量是否以及如何影响过度运动期间的成骨阈值。这项研究将为应力条件下发育中的骨的行为以及成骨运动阈值的存在提供新的证据。

Our understanding of the mechanisms that drive bone mineral acquisition in humans is still limited. Although we, and others, have shown that bone is particularly responsive to exercise during growth, and that overtraining is linked to impaired bone integrity, the threshold at which beneficial physical activity progresses to excessive exercise, with respect to bone, is poorly understood. The long-term objective of our research program is to examine the effects of different type, intensity and duration of exercise on the time course and mechanism(s) involved in the development and adaptive response(s) of bone in children, adolescents and young adults. We hypothesize that: a) there is an age/maturity and sex dependent, optimal range of exercise intensities and durations, and as well level of dietary (energy) intake, that favor the balance between bone formation and bone resorption leading to positive bone adaptation, and b) there is an osteogenic exercise threshold at which excessive exercise tips the balance in favor of bone resorption leading to negative bone adaptation, and which is dependent on sex and skeletal maturity and influenced by dietary energy availability. We will monitor the bone response by means of biochemical (blood) markers that reflect changes in metabolic status of bone, allowing the investigation of the acute effects of exercise on bone. Of particular interest are non-traditional markers of bone turnover including sclerostin, and the ratio of osteoprotegerin (OPG) and receptor activator of nuclear factor ?B ligand (RANKL). ******The methodology includes a series of human studies carried out in two phases. The first phase is a series of exercise trials that will examine differences in the acute biochemical responses of bone turnover to various exercise protocols (low vs. high impact) in children, adolescents and young adults of both sexes. Blood samples will be collected prior to exercise, 5 minutes, 1 hour, and 24 hours post-exercise as previously done in our lab, and they will be analyzed for bone formation and resorption markers, including sclerostin and OPG/RANKL, and additional systemic hormonal and inflammatory factors. The second phase includes a series of exercise trials that will examine changes in markers of bone turnover, with focus on sclerostin and OPG/RANKL ratio, in response to moderate versus excessive exercise (high and low impact), in boys and girls, young men and women. We will manipulate the dietary intake (caloric restriction versus regular diet) in young men and women in order to potentially determine if and how dietary intake affects the osteogenic threshold during excessive exercise. This research will offer new evidence about the behavior of the developing bone under stress conditions, and the existence of an osteogenic exercise threshold.