Lanyon L E
Royal Veterinary College, University of London, UK.
Bone. 1996 Jan;18(1 Suppl):37S-43S. doi: 10.1016/8756-3282(95)00378-9.
There is increasing evidence that load-bearing is an important, if not the most important, functional influence on bone mass and architecture. Load-bearing most probably exerts its influence through the dynamic strains engendered in the bone tissue. Mechanically adaptive bone modeling and remodeling can be regarded as a homeostatic mechanism regulating functional bone strains at each location throughout the skeleton. Because most long bones are loaded in a certain amount of bending normal function, strains vary across the bones' cross-section. Both the longitudinal curvature and cross-sectional shape of a number of bones engender strains during functional loading rather than reduce them. Bone's adaptive response to load-bearing therefore results in functional strains which are neither uniform in distribution nor minimal in magnitude. Not all aspects of bone's strain environment are equally effective as influences on bone architecture. Unusual strain distributions, high strains, and high strain rates seem to be particularly osteogenic. The osteogenic response which follows exposure to such strains appears to saturate after only a few loading cycles. This is consistent with adaptive bone (re)modeling being sensitive to strain "errors," which are not repeated frequently, rather than the repetitious strain cycles engendered during normal predominant activities. Exercise regimens designed to control bone architecture can usefully capitalize on this feature of the adaptive (re)modeling response. Each exercise session need not be prolonged but should include as many novel strain distributions as possible, preferably involving high peak strains and strain rates. To maintain any level of bone mass requires a continued, loading-related osteoregulatory stimulus. Exposure to appropriate load-bearing exercise needs therefore to be repeated, probably at daily or alternate-daily intervals. In short-term experiments in rat bones, estrogen amplifies the osteogenic response to a single period of loading. The features of postmenopausal bone loss are consistent with the etiology of the condition being primarily withdrawal of estrogen's contribution to bone's mechanically adaptive response.
越来越多的证据表明，负重即便不是对骨量和骨结构最重要的功能影响因素，也是重要的功能影响因素。负重很可能是通过骨组织中产生的动态应变发挥其影响的。机械适应性骨建模和重塑可被视为一种稳态机制，在整个骨骼的每个位置调节功能性骨应变。由于大多数长骨在正常功能下会承受一定量的弯曲负荷，应变在骨骼横截面上各不相同。许多骨骼的纵向曲率和横截面形状在功能负荷期间会产生应变而非减少应变。因此，骨骼对负重的适应性反应会导致功能性应变，其分布既不均匀，幅度也不是最小的。并非骨骼应变环境的所有方面对骨结构的影响都同样有效。异常的应变分布、高应变和高应变率似乎特别具有成骨作用。暴露于此类应变后出现的成骨反应似乎在仅几个加载周期后就会饱和。这与适应性骨（再）建模对“误差”应变敏感一致，这种应变不会频繁重复，而不是正常主要活动期间产生的重复性应变周期。旨在控制骨结构的运动方案可以有效地利用适应性（再）建模反应的这一特征。每次运动时间无需延长，但应包括尽可能多的新颖应变分布，最好涉及高峰应变和应变率。要维持任何水平的骨量都需要持续的、与负荷相关的骨调节刺激。因此，可能需要每天或隔天重复进行适当的负重运动。在对大鼠骨骼进行的短期实验中，雌激素会增强对单个加载期的成骨反应。绝经后骨质流失的特征与该病的病因主要是雌激素对骨骼机械适应性反应的贡献减少一致。
