Bamman M M, Clarke M S, Feeback D L, Talmadge R J, Stevens B R, Lieberman S A, Greenisen M C
Department of Human Studies, University of Alabama at Birmingham 35294, USA.
J Appl Physiol (1985). 1998 Jan;84(1):157-63. doi: 10.1152/jappl.1998.84.1.157.
Because resistance exercise (REx) and bed-rest unloading (BRU) are associated with opposing adaptations, our purpose was to test the efficacy of REx against the effects of 14 days of BRU on the knee-extensor muscle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx (n = 8). REx performed five sets of leg press exercise with 80-85% of one repetition maximum (1 RM) every other day during BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined immunohistochemically with three monoclonal antibodies against myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further assessed by quantitative gel electrophoresis. Dynamic 1-RM leg press and unilateral maximum voluntary isometric contraction (MVC) were determined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions (P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased (P < 0.05) in REx from 9 to 2% and did not change in NoEx. 1 RM was reduced (P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to-antagonist root mean squared electromyogram ratio decreased (P < 0.05) 19% in REx. RTD slowed (P < 0.05) by 54% in NoEx only. Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce shifts in myosin phenotype. The reported benefits of REx may prove useful in prescribing exercise for astronauts in microgravity.
由于抗阻运动（REx）和卧床休息去负荷（BRU）会引发相反的适应性变化，我们的目的是测试REx对抗14天BRU对膝伸肌肌群影响的效果。16名健康男性被随机分为不运动组（NoEx；n = 8）或REx组（n = 8）。在BRU期间，REx组每隔一天进行五组腿举练习，负荷为一次重复最大值（1 RM）的80 - 85%。通过经皮针刺活检从股外侧肌采集肌肉样本。使用三种抗肌球蛋白重链（MHC）同工型（I、IIa、IIx）的单克隆抗体通过免疫组织化学方法确定肌纤维分布。通过定量凝胶电泳进一步评估MHC分布。测定动态1 RM腿举和单侧最大自主等长收缩（MVC）。在MVC期间测量最大神经激活（均方根肌电图）和扭矩发展速率（RTD）。在NoEx组中发现I型（15%）和II型（17%）肌纤维横截面积减小（P < 0.05），而REx组未出现这种情况。电泳显示MHC同工型分布没有变化。REx组中IIx型肌纤维的百分比从9%降至2%（P < 0.05），NoEx组则没有变化。NoEx组的1 RM降低了9%（P < 0.05），而REx组没有变化。NoEx组和REx组的MVC分别下降了15%和13%。REx组中激动剂与拮抗剂均方根肌电图比值下降了19%（P < 0.05）。仅NoEx组的RTD减慢了54%（P < 0.05）。结果表明，REx可预防BRU诱导的肌纤维萎缩，并维持特定训练的力量。与太空飞行不同，BRU不会诱导肌球蛋白表型的转变。REx的上述益处可能对为微重力环境下的宇航员制定运动方案有用。
