Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham , Birmingham , United Kingdom.
Department of Sports Medicine and Sports Orthopaedics, University of Potsdam , Potsdam , Germany.
J Appl Physiol (1985). 2018 Apr 1;124(4):1071-1079. doi: 10.1152/japplphysiol.01115.2017. Epub 2018 Feb 8.
Surface electromyographic (EMG) signal amplitude is typically used to compare the neural drive to muscles. We experimentally investigated this association by studying the motor unit (MU) behavior and action potentials in the vastus medialis (VM) and vastus lateralis (VL) muscles. Eighteen participants performed isometric knee extensions at four target torques [10, 30, 50, and 70% of the maximum torque (MVC)] while high-density EMG signals were recorded from the VM and VL. The absolute EMG amplitude was greater for VM than VL ( P < 0.001), whereas the EMG amplitude normalized with respect to MVC was greater for VL than VM ( P < 0.04). Because differences in EMG amplitude can be due to both differences in the neural drive and in the size of the MU action potentials, we indirectly inferred the neural drives received by the two muscles by estimating the synaptic inputs received by the corresponding motor neuron pools. For this purpose, we analyzed the increase in discharge rate from recruitment to target torque for motor units matched by recruitment threshold in the two muscles. This analysis indicated that the two muscles received similar levels of neural drive. Nonetheless, the size of the MU action potentials was greater for VM than VL ( P < 0.001), and this difference explained most of the differences in EMG amplitude between the two muscles (~63% of explained variance). These results indicate that EMG amplitude, even following normalization, does not reflect the neural drive to synergistic muscles. Moreover, absolute EMG amplitude is mainly explained by the size of MU action potentials. NEW & NOTEWORTHY Electromyographic (EMG) amplitude is widely used to compare indirectly the strength of neural drive received by synergistic muscles. However, there are no studies validating this approach with motor unit data. Here, we compared between-muscles differences in surface EMG amplitude and motor unit behavior. The results clarify the limitations of surface EMG to interpret differences in neural drive between muscles.
表面肌电（EMG）信号幅度通常用于比较肌肉的神经驱动。我们通过研究股直肌（VM）和股外侧肌（VL）中的运动单位（MU）行为和动作电位来实验性地研究这种关联。18 名参与者在四个目标扭矩[10、30、50 和 70%的最大扭矩（MVC）]下进行等长膝关节伸展，同时从 VM 和 VL 记录高密度 EMG 信号。VM 的绝对 EMG 幅度大于 VL（P<0.001），而相对于 MVC 归一化的 EMG 幅度则大于 VL（P<0.04）。由于 EMG 幅度的差异可能既源于神经驱动的差异，也源于 MU 动作电位的大小，我们通过估计相应运动神经元池接收到的突触输入，间接推断出这两块肌肉接收到的神经驱动。为此，我们分析了在两种肌肉中通过募集阈值匹配的运动单位从募集到目标扭矩的放电率增加。该分析表明，两块肌肉接收到相似水平的神经驱动。尽管如此，VM 的 MU 动作电位幅度大于 VL（P<0.001），这种差异解释了两块肌肉之间 EMG 幅度的大部分差异（~63%的可解释方差）。这些结果表明，即使经过归一化，EMG 幅度也不能反映协同肌肉的神经驱动。此外，绝对 EMG 幅度主要由 MU 动作电位的大小决定。新的和值得注意的是，肌电图（EMG）幅度广泛用于间接比较协同肌肉接收到的神经驱动强度。然而，目前还没有研究用运动单位数据验证这种方法。在这里，我们比较了表面 EMG 幅度和运动单位行为之间的肌肉间差异。研究结果阐明了表面 EMG 解释肌肉间神经驱动差异的局限性。
