Lester Bridget E, Standley Robert A, Lee Jonah D, Fink William J, Trappe Scott W, Trappe Todd A
Human Performance Laboratory, Ball State University, Muncie, IN 47306, USA.
Aviat Space Environ Med. 2013 Aug;84(8):789-96. doi: 10.3357/asem.3440.2013.
Studies of real and simulated microgravity exposure show the lower limb muscles atrophy to the greatest extent, with the calf muscles being most affected and most difficult to target with exercise countermeasures. This ground-based study examined the metabolic involvement of the thigh and calf muscles during two cycle exercise protocols (moderate and high intensity) central to the exercise countermeasures program on the International Space Station.
Intramuscular glycogen and triglyceride levels were quantified in the vastus lateralis and soleus muscles before and after a moderate (current ISS prescription: 45 min at 55% VO(2max), 131 +/- 12 W) and high (proposed ISS prescription: 8 x 30-s intervals at 150% VO(2max), 459 +/- 34 W) intensity cycle exercise bout in nine individuals.
During moderate intensity cycling, glycogen was significantly reduced in the vastus lateralis (114 +/- 27 mmol x kg(-1) dry weight) and remained unchanged in the soleus. High intensity cycling significantly reduced glycogen in both muscles, but the vastus lateralis (151 +/- 25 mmol x kg(-1) dry weight) used significantly more (-160%) than the soleus (59 +/- 11 mmol x kg(-1) dry weight). Intramuscular triglycerides were unchanged in both muscles at both intensities.
These findings, coupled with other ground-based studies, provide strong support for high intensity cycling being a more appropriate component of the ISS prescription for upper and lower leg skeletal muscle health and cardiorespiratory fitness, although additional exercise paradigms that target the calf are warranted. These muscle-specific findings should be considered when designing exercise strategies for combating conditions of sarcopenia and muscle wasting on Earth.
对真实和模拟微重力暴露的研究表明，下肢肌肉萎缩程度最大，小腿肌肉受影响最严重，且最难通过运动对策进行针对性锻炼。这项地面研究考察了国际空间站运动对策计划核心的两种周期运动方案（中等强度和高强度）期间大腿和小腿肌肉的代谢参与情况。
对9名个体在进行一次中等强度（当前国际空间站规定：以55%的最大摄氧量运动45分钟，功率为131±12瓦）和高强度（提议的国际空间站规定：以150%的最大摄氧量进行8次30秒的间歇运动，功率为459±34瓦）的周期运动前后，测定股外侧肌和比目鱼肌内的糖原和甘油三酯水平。
在中等强度骑行过程中，股外侧肌糖原显著减少（114±27毫摩尔/千克干重），比目鱼肌糖原保持不变。高强度骑行使两块肌肉中的糖原均显著减少，但股外侧肌（151±25毫摩尔/千克干重）的消耗量（-160%）显著高于比目鱼肌（59±11毫摩尔/千克干重）。两种强度下，两块肌肉内的甘油三酯均未发生变化。
这些发现与其他地面研究相结合，有力地支持了高强度骑行作为国际空间站处方中更适合上下腿部骨骼肌健康和心肺功能的组成部分，尽管还需要针对小腿的其他运动模式。在设计对抗地球上肌肉减少症和肌肉萎缩状况的运动策略时，应考虑这些特定肌肉的研究结果。
