Human Performance Laboratory, Ball State University, Muncie, IN.
Universities Space Research Association, Division of Space Life Sciences, NASA Johnson Space Center, Houston, TX.
Med Sci Sports Exerc. 2018 Sep;50(9):1950-1960. doi: 10.1249/MSS.0000000000001620.
This investigation evaluated myocellular responses to an integrated resistance and aerobic training program during 70 d of bed rest.
Training was 6 d·wk on a small-footprint gravity-independent flywheel resistance and aerobic device; 3 d of maximal flywheel supine quadriceps and calf exercises with continuous rowing separated by 4 to 6 h, and 3 d of interval rowing. Vastus lateralis (VL) and soleus (SOL) muscle biopsies were obtained from eight healthy males (age, 28 ± 4 yr; BMI, 25 ± 3 kg·m; V˙O2max, 42 ± 6 mL·kg·min) before and after 6° head-down tilt bed rest. Vastus lateralis and SOL myosin heavy chain (MHC) I and IIa single muscle fiber size and functional characteristics, as well as overall fiber type distribution, capillarization, and metabolic enzyme activities were evaluated.
In the VL, MHC I size and power (absolute and normalized) were preserved. The MHC IIa fibers hypertrophied (+6%, P < 0.05) without a change in absolute power, so normalized power declined (-7%, P < 0.05). In the SOL, MHC I fibers atrophied (-9%) and absolute power declined (-17%) (P < 0.05), whereas normalized power was maintained. Size, absolute power, and normalized power were protected in the less-abundant MHC IIa fibers. Reduced MHC coexpressing hybrid fibers, generally indicative of an exercise training effect, was apparent in the VL, whereas fiber type was maintained in the SOL. Capillarization and metabolic enzymes were generally preserved or increased in VL and SOL.
The integrated resistance and aerobic training protocol on a device maintains several key myocellular characteristics during prolonged unloading, but further refinement of the exercise approach to fully protect the SOL is warranted.
本研究评估了在 70 天卧床休息期间，综合抗阻和有氧训练方案对肌细胞的反应。
训练采用小占地面积、无重力依赖的飞轮抗阻和有氧设备，每周 6 天；3 天最大负荷仰卧位股四头肌和小腿练习，飞轮练习和连续划船练习之间间隔 4 至 6 小时，3 天进行间歇划船练习。从 8 名健康男性（年龄 28 ± 4 岁；BMI 25 ± 3 kg·m；最大摄氧量 42 ± 6 mL·kg·min）中获取股外侧肌（VL）和比目鱼肌（SOL）肌肉活检，在 6°头低位卧床休息前后进行评估。评估股外侧肌和比目鱼肌肌球蛋白重链（MHC）I 和 IIa 单肌纤维大小和功能特性，以及整体纤维类型分布、毛细血管化和代谢酶活性。
在 VL 中，MHC I 大小和功率（绝对和归一化）得到保持。MHC IIa 纤维出现肥大（+6%，P < 0.05），而绝对功率不变，因此归一化功率下降（-7%，P < 0.05）。在 SOL 中，MHC I 纤维萎缩（-9%），绝对功率下降（-17%）（P < 0.05），而归一化功率保持不变。较少的 MHC 共表达混合纤维的大小、绝对功率和归一化功率得到保护。VL 中明显出现了减少的 MHC 共表达混合纤维，这通常表明运动训练的效果，而 SOL 中纤维类型保持不变。VL 和 SOL 中的毛细血管化和代谢酶通常得到保持或增加。
在设备上进行的综合抗阻和有氧训练方案可在长时间卸载期间保持多个关键的肌细胞特征，但需要进一步改进运动方法以完全保护 SOL。
