Mechanosensitivity of the rat skeleton decreases after a long period of loading, but is improved with time off
Mechanosensitivity of the rat skeleton decreases after a long period of loading, but is improved with time off
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DOI：
10.1016/j.bone.2004.12.001
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发表时间：
2005-03-01
期刊：
影响因子：
4.1
通讯作者：
Turner, CH
中科院分区：
文献类型：
--
作者：
Saxon, LK;Robling, AG;Turner, CH
在最初适应大的机械负荷后，骨骼对运动的反应似乎开始减弱。为了抵消长期机械负荷的减弱效应，可能需要“休息”来提高骨细胞对未来机械信号的反应性并重新启动骨形成。本研究的目的是确定骨是否对长期机械负荷变得不那么敏感，以及是否需要休息一段时间来改善机械敏感性。57只雌性SD大鼠（7-8月龄）随机分为以下组之一：第I组施加负荷5周，然后休息10周（1 × 5）;第2组施加负荷5周，然后休息5周，再负荷5周（2 × 5）;第3组连续施加负荷15周（3 × 5）;第4组为年龄匹配对照组，第5组为基线对照组。在右侧尺骨上施加轴向载荷，每天360次循环，频率为2 Hz，每周3天，载荷为15 N。在干预结束时，所有三个负荷组显示出响应于机械负荷的骨量、皮质面积和I-MIN的相似增加。对于所有三个负荷组，负荷尺骨的骨形成率在负荷的前5周增加;然而，在最后5周期间，仅在有时间休息的组（2 × 5）中显著增加（P < 0.05）。与负荷5周（1 x 5）和整个15周（3 X 5）的组相比，休息时间（2 x 5）的组在工作失败方面也表现出更大的改善。第二个实验表明，骨骼上长期负荷的减弱效应并不是衰老的结果。总之，机械负荷的大鼠尺骨的结果在大的改善骨形成在前5周的负荷，但持续负荷降低成骨反应。休息一段时间可以增加骨形成，提高抗骨折能力。(c)2004爱思唯尔公司All rights reserved.
After the initial adaptation to large mechanical loads, it appears as though the skeleton's responsiveness to exercise begins to wane. To counteract the waning effects of long-term mechanical loading, "time off" may be needed to improve the responsiveness of bone cells to future mechanical signals and reinitiate bone formation. The aim of this study was to determine whether bone becomes less sensitive to long-term mechanical loading and whether time off is needed to improve mechanosensitivity. Fifty-seven female Sprague-Dawley rats (7-8 months of age) were randomized to one of following groups: Group I loading was applied for 5 weeks followed by 10 weeks of time off (1 x 5); Group 2 loading was applied for 5 weeks, followed by time off for 5 weeks and loading again for 5 weeks (2 x 5); Group 3 loading was applied continuously for 15 weeks (3 x 5); Group 4 age-matched control group- and Group 5 baseline control group. An axial load was applied to the right ulna for 360 cycles/day, at 2 Hz, 3 days/week at 15 N. At the end of the intervention, all three loaded groups showed similar increases in bone mass, cortical area, and I-MIN in response to mechanical loading, Bone formation rate of the loaded ulna was increased in the first 5 weeks of loading for all three loaded groups; however, during the last 5 weeks, it was only significantly increased in the group that had time off (2 x 5) (P < 0.05). The group that had time off (2 x 5) also showed greater improvements in work to failure compared to the group loaded for 5 weeks (1 x 5) and the entire 15 weeks (3 X 5). A second experiment showed that the waning effect of long-term loading on the skeleton is not a result of aging. In conclusion, mechanical loading of the rat ulna results in large improvements in bone formation during the first 5 weeks of loading, but continual loading decreases the osteogenic response. Having time off increases bone formation and improves the resistance to fracture. (c) 2004 Elsevier Inc. All rights reserved.