This study compared the effects of fatigue on corticospinal responsiveness in the upper- and lower-limb muscles of the same participants. Seven healthy males performed a 2-min maximal voluntary isometric contraction of the elbow flexors or knee extensors on four separate days. Electromyographic responses were elicited by nerve stimulation (maximal M-wave) in all sessions and by transcranial magnetic stimulation (motor-evoked potential; silent period) and spinal tract stimulation (cervicomedullary or thoracic motor-evoked potentials; silent period) in one session each per limb. During sustained maximal voluntary contractions, motor-evoked potential area normalised to M-waves increased from baseline in biceps brachii (155 ± 55%) and rectus femoris (151 ± 44%) (both p ≤ 0.045). At the end of maximal voluntary contractions, spinal tract motor-evoked potential area normalised to M-waves was smaller than baseline in biceps brachii (74 ± 23%; p = 0.012) but not rectus femoris (108 ± 40%; p = 0.999). The ratio of motor-evoked potential to spinal tract-evoked potential areas increased dramatically from 90 to 115 s in biceps brachii (p = 0.001) but not in rectus femoris (p = 0.999). Silent period durations increased similarly in both muscles (p ≤ 0.008) after transcranial and spinal stimulation. Sustained maximal contractions elicit different neurophysiological adjustments in upper- and lower-limb muscles. Specifically, motoneuronal excitability was reduced in biceps brachii, but not in rectus femoris, and this reduction required greater compensatory adjustments from the motor cortex. Therefore, changes in cortical and spinal excitability during sustained maximal exercise are likely specific to the muscle performing the task.

译文

这项研究比较乏力对同一参与者上肢和下肢肌肉皮质脊髓反应性的影响。七名健康男性在四个不同的日子里对肘部屈肌或膝伸肌进行了2分钟的最大自愿等距收缩。在所有会话中通过神经刺激 (最大M波) 以及经颅磁刺激 (运动诱发电位; 静默期) 和脊髓道刺激 (颈髓或胸腔运动诱发电位; 静默期) 引起肌电图反应每个肢体。在持续最大自愿收缩期间,肱二头肌 (155   ±   55%) 和股直肌 (151   ±   44%) (均p  ≤   0.045) 的运动诱发电位区域从基线增加到M波。在最大自愿性收缩结束时,肱二头肌 (74   ±   23%; P   =   0.012) 的脊髓道运动诱发电位面积标准化为M波,小于基线,而股直肌 (108   ±   40%; P   =   0.999)。肱二头肌 (p   =   0.001) 的运动诱发电位与脊髓束诱发电位区域的比率从90到115  s急剧增加,而股直肌 (p   =   0.999) 则没有。经颅和脊柱刺激后,两种肌肉的静默期持续时间相似地增加 (p  ≤   0.008)。持续的最大收缩会引起上肢和下肢肌肉的不同神经生理调节。具体来说,肱二头肌的运动神经元兴奋性降低,但股直肌却没有,这种降低需要运动皮层进行更大的补偿性调整。因此,持续最大运动期间皮质和脊柱兴奋性的变化可能是特定于执行任务的肌肉的。

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