As voluntary muscle fatigue increases, the perception of the effort required to produce a particular level of force also increases. This occurs because we produce greater neural outputs from the brain to compensate for the fatigue-induced loss of force. Muscle fatigue can also be generated following bouts of neuromuscular electrical stimulation (NMES), a technique widely used for rehabilitation and training purposes. Yet the effects of NMES-induced fatigue on the perception of effort have never been tested. In this study, we thus evaluated how electrically evoked fatigue would affect the sense of effort. For this purpose, we used two psychophysical tasks intended to assess effort perception: (i) a bilateral matching task in which subjects were asked to contract the elbow flexors of their reference and indicator arms with similar amounts of effort and (ii) a unilateral matching task in which they produced controlled levels of isometric force with their indicator arm and rated their perceived effort using the Borg CR10 scale. These tasks were performed before and after the biceps brachii of the indicator arm was submitted to a fatiguing NMES program that generated maximal force losses of 10–15%. Contrary to voluntary muscle fatigue, the sense of effort decreased post-NMES in both tasks despite increased neural outputs to the elbow flexors of the fatigued indicator arm. This shows that the relationship between motor command magnitude and effort perception was completely modified by NMES. It is proposed that NMES alters the sensory structures responsible for effort signal integration.

随着自愿性肌肉疲劳的增加，对产生特定水平的力量所需的努力的感觉也随之增加。发生这种情况是因为我们从大脑产生了更大的神经输出，以补偿疲劳引起的力量损失。反复进行神经肌肉电刺激（NMES）后，也会产生肌肉疲劳，这是一种广泛用于康复和训练目的的技术。然而，从未测试过NMES引起的疲劳对努力感知的影响。因此，在这项研究中，我们评估了电诱发的疲劳将如何影响努力感。为此，我们使用了两个心理物理任务来评估努力感知：（i）一项双边匹配任务，其中要求受试者以相似的力度收缩其参考臂和指示器臂的肘屈肌；以及（ii）一项单方面匹配任务，其中受试者用其指示臂和手臂产生受控水平的等轴测力使用Borg CR10量表评估他们的感知努力。这些任务是在指示器臂的肱二头肌肱肌接受疲劳的NMES程序之前和之后执行的，该程序产生的最大力损失为10％至15％。与自愿性肌肉疲劳相反，在NMES之后的两个任务中，尽管疲劳的指示器臂的肘部屈肌的神经输出增加，但努力的感觉却降低了。这表明，NMES完全修改了运动命令幅度与努力感知之间的关系。