Leterme D, Casasnovas B
Laboratoire de Physiologie Neuromusculaire, Université du Littoral - Côte d'Opale, Calais, France.
Eur J Appl Physiol Occup Physiol. 1999 Mar;79(4):312-7. doi: 10.1007/s004210050513.
Contractile and fatigue-resistance properties of 71 lateral gastrocnemius muscle (LG) motor units (MU) following 14 days of hindlimb unloading (HU) were compared to those of 60 LG MU from control rats. The MU properties were assessed from isolated and stimulated individual motor axons. The MU were classified using standard criteria (shape of unfused tetani and fatigue resistance). The HU did not affect LG MU composition, but diminished the maximal tetanic tension (Po) of all MU types: P0 was significantly reduced by about 40% for the slow and fast-resistant MU, and by 18% for the fast-fatigable ones. The speed-related properties of fast-resistant MU became more similar to those of slower MU. The fatigue properties of MU were evaluated during a 5-min exercise test, using two fatigue indexes, FI2 and FI5, which expressed the relative capacity of MU to generate tension after 2 and 5 min, respectively. Results showed that 14 days of HU did not change the fatigue sensitivity of the LG MU. However, when F15 was compared to FI2, a greater decrease was observed after HU than in control conditions for the fast-resistant and fast-intermediate MU. It was concluded that a prolonged fatigue test may show changes in metabolic properties of muscle fibres during 14 days of HU. Specific adaptations of LG MU as well as comparisons with those of the soleus muscle under the same conditions are discussed.
将后肢卸载（HU）14天的71个外侧腓肠肌（LG）运动单位（MU）的收缩和抗疲劳特性与60个对照大鼠的LG运动单位的特性进行了比较。通过分离和刺激单个运动轴突来评估运动单位的特性。使用标准标准（未融合强直收缩的形状和抗疲劳性）对运动单位进行分类。HU并未影响LG运动单位的组成，但降低了所有类型运动单位的最大强直张力（Po）：慢肌和抗疲劳快肌运动单位的Po显著降低约40%，易疲劳快肌运动单位的Po降低18%。抗疲劳快肌运动单位与速度相关的特性变得更类似于慢肌运动单位。在5分钟的运动测试中，使用两个疲劳指数FI2和FI5评估运动单位的疲劳特性，这两个指数分别表示运动单位在2分钟和5分钟后产生张力的相对能力。结果表明，14天的HU并未改变LG运动单位的疲劳敏感性。然而，当将F15与FI2进行比较时，与对照条件相比，HU后抗疲劳快肌和中间型快肌运动单位的下降幅度更大。得出的结论是，长时间的疲劳测试可能会显示出HU 14天期间肌肉纤维代谢特性的变化。讨论了LG运动单位的特异性适应以及在相同条件下与比目鱼肌运动单位的比较。
