National Advisory Unit on Occupational Rehabilitation, Rauland, Norway.
Department of Research, Sunnaas Rehabilitation Hospital, Oslo, Norway.
Scand J Med Sci Sports. 2020 Aug;30(8):1298-1317. doi: 10.1111/sms.13675. Epub 2020 May 4.
The main objective of this systematic review was to examine the effect of reduced muscle activity on the relative number of type 1 muscle fibers (%) in the human vastus lateralis muscle. Other objectives were changes in type 2A and 2X percentages and muscle fiber cross-sectional area. We conducted systematic literature searches in eight databases and included studies assessing type 1 fiber percentage visualized by ATPase or immunohistochemical staining before and after a period (≥14 days) of reduced muscle activity. The reduced muscle activity models were detraining, leg unloading, and bed rest. Forty-two studies comprising 451 participants were included. Effect sizes were calculated as the mean difference between baseline and follow-up and Generic Inverse Variance tests with random-effects models were used for the weighted summary effect size. Overall, the mean type 1 muscle fiber percentage was significantly reduced after interventions (-1.94%-points, 95% CI [-3.37, -0.51], P = .008), with no significant differences between intervention models (P = .86). Meta-regression showed no effect of study duration on type 1 fiber percentage (P = .98). Conversely, the overall type 2X fiber percentage increased after reduced muscle activity (P < .001). The CSA of the muscle fiber types decreased after the study period (all P-values < 0.001) with greater reductions in type 2 than type 1 fibers (P < .001). The result of this meta-analysis display that the type 1 muscle fiber percentage decrease as a result of reduced muscle activity, although the effect size is relatively small.
本系统评价的主要目的是研究肌肉活动减少对人体股外侧肌 1 型肌纤维（%）相对数量的影响。其他目的是研究 2A 型和 2X 型百分比以及肌纤维横截面积的变化。我们在八个数据库中进行了系统文献检索，纳入了评估肌肉活动减少（≥14 天）前后通过 ATP 酶或免疫组织化学染色观察到的 1 型纤维百分比的研究。肌肉活动减少的模型包括停训、腿部去负荷和卧床休息。共纳入 42 项研究，包含 451 名参与者。效应大小的计算方法为基线与随访之间的均数差值，采用随机效应模型的广义倒数方差检验进行加权汇总效应大小的检验。总体而言，干预后 1 型肌纤维百分比显著降低（-1.94%，95%CI [-3.37，-0.51]，P =.008），不同干预模型之间无显著差异（P =.86）。元回归分析显示，研究持续时间对 1 型纤维百分比无影响（P =.98）。相反，肌肉活动减少后 2X 型肌纤维百分比总体增加（P <.001）。研究期间，肌纤维类型的 CSA 均降低（所有 P 值均<.001），2 型肌纤维比 1 型肌纤维降低更多（P <.001）。这项荟萃分析的结果表明，肌肉活动减少导致 1 型肌纤维百分比下降，尽管效应量相对较小。
