Legs + Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, Illinois.
Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, Illinois.
J Appl Physiol (1985). 2021 Jan 1;130(1):269-281. doi: 10.1152/japplphysiol.00653.2020. Epub 2020 Nov 26.
The interindividual variability in the neural drive sent from the spinal cord to muscles is largely unknown, even during highly constrained motor tasks. Here, we investigated individual differences in the strength of neural drive received by the vastus lateralis (VL) and vastus medialis (VM) during an isometric task. We also assessed the proportion of common neural drive within and between these muscles. Twenty-two participants performed a series of submaximal isometric knee extensions at 25% of their peak torque. High-density surface electromyography recordings were decomposed into motor unit action potentials. Coherence analyses were applied on the motor unit spike trains to assess the degree of neural drive that was shared between motor neurons. Six participants were retested ∼20 mo after the first session. The distribution of the strength of neural drive between VL and VM varied between participants and was correlated with the distribution of normalized interference electromyography (EMG) signals ( > 0.56). The level of within- and between-muscle coherence varied across individuals, with a significant positive correlation between these two outcomes (VL: = 0.48; VM: = 0.58). We also observed a large interindividual variability in the proportion of muscle-specific drive, that is, the drive unique to each muscle (VL range: 6%-83%, VM range: 6%-86%). All the outcome measures were robust across sessions, providing evidence that the individual differences did not depend solely on the variability of the measures. Together, these results demonstrate that the neural strategies to control the VL and VM muscles widely vary across individuals, even during a constrained task. We observed that the distribution of the strength of neural drive between the vastus lateralis and vastus medialis during a single-joint isometric task varied across participants. Also, we observed that the proportion of neural drive that was shared within and between these muscles also varied across participants. These results provide evidence that the neural strategies to control the vastus lateralis and vastus medialis muscles widely vary across individuals, even during a mechanically constrained task.
个体间脊髓向肌肉传递的神经驱动的可变性在很大程度上是未知的，即使在高度受限的运动任务中也是如此。在这里，我们研究了在等长任务中股外侧肌（VL）和股中间肌（VM）接收到的神经驱动强度的个体差异。我们还评估了这些肌肉内部和之间共同神经驱动的比例。22 名参与者以其峰值扭矩的 25%进行了一系列亚最大等长膝关节伸展。高密度表面肌电图记录被分解为运动单位动作电位。相干分析应用于运动单位尖峰序列，以评估运动神经元之间共享的神经驱动程度。六名参与者在第一次会议后约 20 个月进行了重新测试。VL 和 VM 之间神经驱动强度的分布在参与者之间有所不同，并且与归一化干扰肌电图（EMG）信号的分布相关（>0.56）。肌肉内和肌肉间相干性的水平在个体之间变化，这两个结果之间存在显著的正相关（VL：=0.48；VM：=0.58）。我们还观察到肌肉特异性驱动的比例（即每个肌肉特有的驱动）存在很大的个体间可变性（VL 范围：6%-83%，VM 范围：6%-86%）。所有的结果测量在整个会议中都是稳健的，这表明个体差异不仅仅取决于测量的可变性。总的来说，这些结果表明，即使在受限制的任务中，个体之间控制 VL 和 VM 肌肉的神经策略也存在广泛差异。我们观察到，在单关节等长任务中，VL 和 VM 之间神经驱动强度的分布在参与者之间有所不同。此外，我们还观察到，这些肌肉内部和之间共享的神经驱动比例也在参与者之间有所不同。这些结果表明，即使在机械受限的任务中，个体之间控制股外侧肌和股中间肌的神经策略也存在广泛差异。
