Department of Human Movement, Social and Health Sciences, University of Rome "Foro Italico" Rome, Italy.
Front Hum Neurosci. 2013 Apr 15;7:135. doi: 10.3389/fnhum.2013.00135. eCollection 2013.
Fatigue has been defined as an exercise-induced decline in force generation capacity because of changes at both the peripheral and central levels. Movement is preceded and accompanied by brain activities related to the preparation and execution of movement (movement related cortical potentials, MRCP), which have been correlated with the perception of effort (RPE). We combined force measurements, surface electromyography (sEMG), peripheral electrical stimulation (maximal twitch, MT) and MRCP analysis to further our understanding of the neural correlates of peripheral and central changes during a fatiguing task involving the lower limbs. Eighteen healthy volunteers performed 4 blocks of isometric knee extensions at 40% of the maximal voluntary contraction (MVC) for a total of 240 2-s contractions. At the baseline and after each block, we measured RPE, MT and MVC. We simultaneously recorded the force of the knee extensor muscles, root mean square (RMS) of the sEMG of the vastus lateralis muscle, and electroencephalography (EEG) from 64 channels. The MRCPs were extracted from the EEG recordings and averaged in the early (Block 1-2) and late (Block 3-4) blocks. Two cohorts were obtained by cluster analysis based on the RPE (i.e., perception of effort) and MT (i.e., peripheral fatigue). We observed a significant decline in both the MVC (-13%) and RMS (-25%) of the sEMG signal over the course of the task; thus, muscle fatigue had occurred in all of the participants regardless of the cohort. The MRCP amplitude was larger in the fatigued than the non-fatigued MT cohort in the supplementary and premotor areas, whereas the MRCP amplitude was larger in the fatigued than the non-fatigued RPE cohort in the aforementioned areas, and also in the primary motor and prefrontal cortices (PFC). The increase in the positive activity of the PFC, along with the perception of effort, represents a novel result, suggesting that it is modulated more by the perception of effort than peripheral fatigue.
疲劳被定义为由于外周和中枢水平的变化导致的力量产生能力的运动诱导下降。运动之前和运动过程中伴随着与运动准备和执行相关的大脑活动（运动相关皮质电位，MRCP），这些活动与努力感（RPE）相关。我们结合力量测量、表面肌电图（sEMG）、外周电刺激（最大抽搐，MT）和 MRCP 分析，以进一步了解涉及下肢的疲劳任务中外周和中枢变化的神经相关性。18 名健康志愿者以最大自主收缩（MVC）的 40%进行 4 组等长膝关节伸展，共 240 个 2 秒收缩。在基线和每个块之后，我们测量了 RPE、MT 和 MVC。我们同时记录了膝关节伸肌的力量、股外侧肌 sEMG 的均方根（RMS）和脑电图（EEG）的 64 个通道。从 EEG 记录中提取 MRCP 并在早期（第 1-2 块）和晚期（第 3-4 块）块中进行平均。基于 RPE（即努力感）和 MT（即外周疲劳）聚类分析获得了两个队列。在任务过程中，MVC（-13%）和 sEMG 信号的 RMS（-25%）均明显下降；因此，所有参与者都发生了肌肉疲劳，而不管队列如何。在补充和运动前区域，MRCP 幅度在疲劳组比非疲劳 MT 组大，而在上述区域以及初级运动皮质和前额叶皮质（PFC），MRCP 幅度在疲劳组比非疲劳 RPE 组大。PFC 的正活动增加，以及努力感的增加，代表了一个新的结果，表明它更多地受到努力感的调节，而不是外周疲劳的调节。
