Srinivasan Sundar, Ausk Brandon J, Poliachik Sandra L, Warner Sarah E, Richardson Thomas S, Gross Ted S
Dept. of Orthopaedics, University of Washington, Seattle, WA 98104-2499, USA.
J Appl Physiol (1985). 2007 May;102(5):1945-52. doi: 10.1152/japplphysiol.00507.2006. Epub 2007 Jan 25.
We hypothesized that a 10-s rest interval (at zero load) inserted between each load cycle would increase the osteogenic effects of mechanical loading near previously identified thresholds for strain magnitude and cycle numbers. We tested our hypothesis by subjecting the right tibiae of female C57BL/6J mice (16 wk, n = 70) to exogenous mechanical loading within a peri-threshold physiological range of strain magnitudes and load cycle numbers using a noninvasive murine tibia loading device. Bone responses to mechanical loading were determined via dynamic histomorphometry. More specifically, we contrasted bone formation induced by cyclic vs. rest-inserted loading (10-s rest at zero load inserted between each load cycle) by first varying peak strains (1,000, 1,250, or 1,600 micro epsilon) at fixed cycle numbers (50 cycles/day, 3 days/wk for 3 wk) and then varying cycle numbers (10, 50, or 250 cycles/day) at a fixed strain magnitude (1,250 micro epsilon). Within the range of strain magnitudes tested, the slope of periosteal bone formation rate (p.BFR/BS) with increasing strain magnitudes was significantly increased by rest-inserted compared with cyclical loading. Within the range of load cycles tested, the slope of p.BFR/BS with increasing load cycles of rest-inserted loading was also significantly increased by rest-inserted compared with cyclical loading. In sum, the data of this study indicate that inserting a 10-s rest interval between each load cycle amplifies bone's response to mechanical loading, even within a peri-threshold range of strain magnitudes and cycle numbers.
我们假设，在每个负荷周期之间插入10秒的休息间隔（零负荷），将增强机械负荷在先前确定的应变幅度和循环次数阈值附近的成骨作用。我们使用非侵入性小鼠胫骨加载装置，在应变幅度和负荷循环次数的阈周生理范围内，对雌性C57BL/6J小鼠（16周龄，n = 70）的右胫骨施加外源性机械负荷，以验证我们的假设。通过动态组织形态计量学确定骨骼对机械负荷的反应。更具体地说，我们通过首先在固定循环次数（每天50次循环，每周3天，共3周）下改变峰值应变（1000、1250或1600微应变），然后在固定应变幅度（1250微应变）下改变循环次数（每天10、50或250次循环），对比循环加载与插入休息的加载（每个负荷周期之间插入零负荷的10秒休息）所诱导的骨形成。在测试的应变幅度范围内，与循环加载相比，插入休息显著增加了骨膜骨形成率（p.BFR/BS）随应变幅度增加的斜率。在测试的负荷循环范围内，与循环加载相比，插入休息也显著增加了插入休息的加载的p.BFR/BS随负荷循环增加的斜率。总之，本研究数据表明，在每个负荷周期之间插入10秒的休息间隔可增强骨骼对机械负荷的反应，即使在应变幅度和循环次数的阈周范围内。
