Maruyama Atsuo, Matsunaga Kaoru, Tanaka Nobuyuki, Rothwell John C
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK.
Clin Neurophysiol. 2006 Apr;117(4):864-70. doi: 10.1016/j.clinph.2005.12.019. Epub 2006 Feb 21.
Central fatigue is the inability of central commands to recruit maximum evocable muscle force during voluntary contraction. Here, we investigate how fatigue affects the inhibitory circuits of the motor cortex.
MEPs, short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated using a paired pulse transcranial magnetic stimulation (TMS) paradigm before, during and after a series of 5 isometric contractions of the FDI muscle to 50% maximal voluntary contraction (MVC). Each contraction lasted 2 min and was separated from the next by a pause of 2 min 40 s. Twelve male healthy subjects (range from 22 to 51 years) participated in experiment 1, in which the intensity of test stimulus was constant throughout the experiment. Eight of the same subjects (range from 26 to 51 years) participated in experiment 2, in which the intensity of test stimulus was adjusted so that the amplitude of the test MEP was kept constant throughout the measurement.
As expected, test MEPs gradually decreased with progressive fatigue and recovered to control values with 5-10 min of rest. Because of the change in MEP amplitude, changes in percent SICI (reduced inhibition) and percent ICF (increased facilitation) in experiment 1 are difficult to interpret. When the test MEP was maintained at a constant size in experiment 2 there was no change in percent ICF, but the reduction in SICI was still present although it recovered to control values within the first 5-10 min of rest.
SICI in FDI decreases transiently after a series of fatiguing isometric contractions. This decrease may compensate to some extent for reduced cortical excitability after muscle fatigue.
中枢性疲劳是指在自主收缩过程中，中枢指令无法募集到最大可诱发肌肉力量的现象。在此，我们研究疲劳如何影响运动皮层的抑制性回路。
在第一背侧骨间肌（FDI）进行5次等长收缩至最大自主收缩（MVC）的50%之前、期间和之后，使用配对脉冲经颅磁刺激（TMS）范式评估运动诱发电位（MEP）、短间隔皮质内抑制（SICI）和皮质内易化（ICF）。每次收缩持续2分钟，每次收缩之间间隔2分40秒。12名健康男性受试者（年龄范围22至51岁）参与实验1，实验过程中测试刺激强度保持恒定。其中8名相同受试者（年龄范围26至51岁）参与实验2，实验中调整测试刺激强度，使测试MEP的幅度在整个测量过程中保持恒定。
正如预期，测试MEP随着疲劳进展逐渐降低，并在休息5 - 10分钟后恢复至对照值。由于MEP幅度的变化，实验1中SICI百分比（抑制减少）和ICF百分比（易化增加）的变化难以解释。在实验2中，当测试MEP保持恒定时，ICF百分比没有变化，但SICI的降低仍然存在，尽管在休息的前5 - 10分钟内恢复至对照值。
在进行一系列疲劳性等长收缩后，FDI中的SICI会短暂降低。这种降低可能在一定程度上补偿肌肉疲劳后皮质兴奋性的降低。
