Space travel and prolonged bed rest are examples of mechanical unloading that induce significant muscle and bone loss. The compromised structure and function of bone and muscle owing to unloading make the reloading period a high risk for injury. To explore interactions between skeletal bone and muscle during reloading, we hypothesized that acute external mechanical loading of bone in combination with re-ambulation facilitates the proportional recovery of bone and muscle lost during hind limb suspension (HLS) unloading. Adult male C57Bl/6J mice were randomly assigned to a HLS or time-matched ground control (GC) group. After 2-weeks of HLS, separate groups of mice were studied at day 14 (no re-ambulation), day 28 (14 days re-ambulation) and day 56 (42 days re-ambulation); throughout the re-ambulation period, one limb received compressive mechanical loading and the contralateral limb served as an internal control. HLS induced loss of trabecular bone volume (BV/TV; −51 ± 2%) and muscle weight (−15 ± 2%) compared to GC at day 14. At day 28, the left tibia (re-ambulation only) of HLS mice had recovered approximately 20% of BV/TV lost during HLS, while the right tibia (re-ambulation and acute external mechanical loading) recovered to GC values of BV/TV (~100% recovery). At day 56, the right tibia continued to recover bone for some outcomes (trabecular BV/TV, trabecular thickness), while the left limb did not. Cortical bone displayed a delayed response to HLS, with a 10% greater decrease in BV/TV at day 28 compared to day 14. In contrast to bone, acute external mechanical loading during the re-ambulation period did not significantly increase muscle mass or protein synthesis in the gastrocnemius, compared to re-ambulation alone. Our results suggest acute external mechanical loading facilitates the recovery of bone during reloading following HLS unloading, but this does not translate to a concomitant recovery of muscle mass.

太空旅行和长时间卧床休息是导致明显的肌肉和骨质流失的机械卸载的例子。由于卸载而导致骨骼和肌肉结构和功能受损，因此重新加载期间很容易受伤。为了探究在重装过程中骨骼与肌肉之间的相互作用，我们假设骨的急性外部机械负载与重新固定相结合，有助于按比例恢复在后肢悬吊（HLS）卸载过程中丢失的骨骼和肌肉。将成年雄性C57Bl / 6J小鼠随机分配到HLS或时间匹配地面对照（GC）组。在HLS 2周后，分别在第14天（不重新行情），第28天（重新行情14天）和第56天（重新行情42天）研究了不同的小鼠组；在整个重整期间，一只肢受到压缩机械负荷，对侧肢作为内部对照。HLS导致小梁骨体积（BV / TV; −51±2％）和肌肉重量（-与第14天的GC相比，差异为15±2％）。在第28天，HLS小鼠的左胫骨（仅重新行am行）已恢复了HLS期间BV / TV丢失的大约20％，而右侧胫骨（重新行进并行and行）。急性外部机械负荷）恢复到BV / TV的GC值（约100％恢复）。在第56天，右胫骨继续恢复骨骼以达到某些结果（小梁BV / TV，小梁厚度），而左肢则没有。皮质骨显示出对HLS的延迟反应，与第14天相比，第28天的BV / TV降低了10％。与骨骼相反，在再植入期间，急性外部机械负荷并未显着增加肌肉质量或蛋白质在腓肠肌中进行合成，相比于单独再行。