Malisoux Laurent, Jamart Cécile, Delplace Krystel, Nielens Henri, Francaux Marc, Theisen Daniel
Institut d'Education Physique et de Réadaptation, Faculté de Médecine, Université Catholique de Louvain, Louvain-la-Neuve, Belgium .
J Appl Physiol (1985). 2007 Jan;102(1):340-9. doi: 10.1152/japplphysiol.00609.2006. Epub 2006 Oct 12.
This study compared human muscles following long-term reduced neuromuscular activity to those with normal functioning regarding single fiber properties. Biopsies were obtained from the vastus lateralis of 5 individuals with chronic (>3 yr) spinal cord injury (SCI) and 10 able-bodied controls (CTRL). Chemically skinned fibers were tested for active and passive mechanical characteristics and subsequently classified according to myosin heavy chain (MHC) content. SCI individuals had smaller proportions of type I (11 +/- 7 vs. 34 +/- 5%) and IIa fibers (11 +/- 6 vs. 31 +/- 5%), whereas type IIx fibers were more frequent (40 +/- 13 vs. 7 +/- 3%) compared with CTRL subjects (P < 0.05). Cross-sectional area and peak force were similar in both groups for all fiber types. Unloaded shortening velocity of fibers from paralyzed muscles was higher in type IIa, IIa/IIx, and IIx fibers (26, 65, and 47%, respectively; P < 0.01). Consequently, absolute peak power was greater in type IIa (46%; P < 0.05) and IIa/IIx fibers (118%; P < 0.01) of the SCI group, whereas normalized peak power was higher in type IIa/IIx fibers (71%; P < 0.001). Ca(2+) sensitivity and passive fiber characteristics were not different between the two groups in any fiber type. Composite values (average value across all fibers analyzed within each study participant) showed similar results for cross-sectional area and peak force, whereas maximal contraction velocity and fiber power were more than 100% greater in SCI individuals. These data illustrate that contractile performance is preserved or even higher in the remaining fibers of human muscles following reduced neuromuscular activity.
本研究比较了长期神经肌肉活动减少后的人体肌肉与功能正常的人体肌肉在单纤维特性方面的差异。从5名患有慢性（>3年）脊髓损伤（SCI）的个体和10名健全对照者（CTRL）的股外侧肌获取活检样本。对化学去膜纤维进行主动和被动力学特性测试，随后根据肌球蛋白重链（MHC）含量进行分类。与CTRL受试者相比，SCI个体的I型纤维（11±7%对34±5%）和IIa型纤维（11±6%对31±5%）比例较小，而IIx型纤维更为常见（40±13%对7±3%）（P<0.05）。两组中所有纤维类型的横截面积和峰值力相似。瘫痪肌肉纤维的无负荷缩短速度在IIa型、IIa/IIx型和IIx型纤维中更高（分别为26%、65%和47%；P<0.01）。因此，SCI组IIa型纤维（46%；P<0.05）和IIa/IIx型纤维（118%；P<0.01）的绝对峰值功率更大，而IIa/IIx型纤维的标准化峰值功率更高（71%；P<0.001）。两组中任何纤维类型的Ca(2+)敏感性和被动纤维特性均无差异。综合值（每个研究参与者分析的所有纤维的平均值）在横截面积和峰值力方面显示出相似的结果，而SCI个体的最大收缩速度和纤维功率则高出100%以上。这些数据表明，在神经肌肉活动减少后，人体肌肉中剩余纤维的收缩性能得以保留甚至更高。
