Pasquet B, Carpentier A, Duchateau J, Hainaut K
Laboratory of Biology, Université Libre de Bruxelles, 28 Avenue P. Héger, CP 168, 1000 Brussels, Belgium.
Muscle Nerve. 2000 Nov;23(11):1727-35. doi: 10.1002/1097-4598(200011)23:11<1727::aid-mus9>3.0.co;2-y.
We compared the contribution of central and peripheral processes to muscle fatigue induced in the ankle dorsiflexor muscles by tests performed during concentric (CON) and eccentric (ECC) conditions. Each fatigue test consisted of five sets of 30 maximum voluntary contractions at a constant speed of 50 degrees /s for a 30 degrees range of motion of the ankle joint. The torque produced by the dorsiflexors and the surface electromyogram (EMG) of the tibialis anterior muscle were recorded during the fatigue tests. Before, during, and after the tests, the compound muscle action potential (M wave) and the contractile properties in response to single and paired electrical stimuli, as well as the interpolated-twitch method and postactivation potentiation (PAP), were recorded during isometric conditions. Compared with ECC contractions, the CON ones resulted in a greater (P < 0.05) loss of force (-31.6% vs. -23.8%) and a decrease in EMG activity (-26.4% vs. -17.5%). This difference was most pronounced during the first four sets of contractions, but was reduced during the last set. Activation was not altered by the tests because neither the interpolated-twitch response nor the ratio of the voluntary EMG to the amplitude of the M wave was changed in the two fatigue tests. Although there was no significant difference in M-wave amplitude between the two tests, changes in the twitch parameters and in the PAP were found to be greater in the CON than ECC contractions. It is concluded that the greater alterations in the contractile properties observed during the CON contractions indicate that intracellular Ca(2+)-controlled excitation-contraction (E-C) coupling processes, possibly associated with a higher energy requirement, are affected to a much greater degree than during ECC contractions.
我们比较了在向心（CON）和离心（ECC）条件下进行的测试中，中枢和外周过程对踝关节背屈肌诱发的肌肉疲劳的贡献。每次疲劳测试包括五组，每组30次最大自主收缩，踝关节在30度运动范围内以50度/秒的恒定速度进行。在疲劳测试期间，记录背屈肌产生的扭矩和胫骨前肌的表面肌电图（EMG）。在测试前、测试期间和测试后，在等长条件下记录复合肌肉动作电位（M波）以及对单电刺激和双电刺激的收缩特性，以及插入式抽搐法和激活后增强（PAP）。与ECC收缩相比，CON收缩导致更大程度（P < 0.05）的力量损失（-31.6% 对 -23.8%）和EMG活动降低（-26.4% 对 -17.5%）。这种差异在前三组收缩中最为明显，但在最后一组收缩中有所减小。测试未改变激活情况，因为在两次疲劳测试中，插入式抽搐反应以及自愿EMG与M波幅度的比值均未改变。尽管两次测试之间M波幅度没有显著差异，但发现CON收缩中抽搐参数和PAP的变化比ECC收缩中更大。得出的结论是，在CON收缩期间观察到的收缩特性的更大变化表明，细胞内Ca(2+)控制的兴奋 - 收缩（E - C）偶联过程，可能与更高的能量需求相关，比ECC收缩期间受到的影响程度要大得多。
