Hug François, Dernoncourt François, Avrillon Simon, Thorstensen Jacob, Besomi Manuela, van den Hoorn Wolbert, Tucker Kylie
Université Côte d'Azur, LAMHESS, Nice, France.
School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia.
J Physiol. 2025 Jun;603(11):3445-3461. doi: 10.1113/JP288504. Epub 2025 May 31.
Pain significantly influences movement, yet the neural mechanisms underlying the range of observed motor adaptations remain unclear. This study combined experimental data and in silico models to investigate the contribution of inhibitory and neuromodulatory inputs to motor unit behaviour in response to nociceptive stimulation during contractions at 30% of maximal torque. Specifically, we aimed to unravel the distribution pattern of inhibitory inputs to the motor unit pool. Seventeen participants performed isometric knee extension tasks under three conditions: Control, Pain (induced by injecting hypertonic saline into the infra-patellar fat pad) and Washout. We identified large samples of motor units in the vastus lateralis (up to 53/participant) from high-density electromyographic signals, leading to three key observations. First, while motor unit discharge rates significantly decreased during Pain, a substantial proportion of motor units (14.8-24.8%) did not show this decrease and, in some cases, even exhibited an increase. Second, using complementary approaches, we found that pain did not significantly affect neuromodulation, making it unlikely to be a major contributor to the observed changes in motor unit behaviour. Third, we observed a significant reduction in the proportion of common inputs to motor units during Pain. To explore potential neurophysiological mechanisms underlying these results, we simulated the behaviour of motor unit pools with varying distribution patterns of inhibitory inputs. Our simulations support the hypothesis that a non-homogeneous distribution of inhibitory inputs, not strictly organised according to motor unit size, is a key mechanism underlying the motor response to nociceptive stimulation during moderate contraction intensity. KEY POINTS: Pain affects movement, but the neural mechanisms underlying these motor adaptations are not well defined. The traditional view is that pain causes uniform (homogeneous) inhibition among motor units. Recent research has observed differential motor unit responses to experimental pain - some with decreased discharge rates and others with increased discharge rates. Combining experimental data with modelling, we provide compelling evidence of increased inhibition that is non-uniformly distributed across motor units, regardless of their size.
疼痛对运动有显著影响，然而，所观察到的一系列运动适应性背后的神经机制仍不清楚。本研究结合实验数据和计算机模型，以探究在最大扭矩的30%收缩期间，抑制性和神经调节性输入对运动单位行为在伤害性刺激响应中的作用。具体而言，我们旨在揭示抑制性输入到运动单位池的分布模式。17名参与者在三种条件下进行等长膝关节伸展任务：对照、疼痛（通过向髌下脂肪垫注射高渗盐水诱导）和洗脱。我们从高密度肌电信号中识别出股外侧肌中大量的运动单位样本（每位参与者多达53个），得出了三个关键观察结果。第一，虽然在疼痛期间运动单位放电率显著降低，但相当一部分运动单位（14.8 - 24.8%）并未出现这种降低，在某些情况下甚至有所增加。第二，使用互补方法，我们发现疼痛并未显著影响神经调节，这使得它不太可能是观察到的运动单位行为变化的主要促成因素。第三，我们观察到在疼痛期间运动单位共同输入的比例显著降低。为了探索这些结果背后潜在的神经生理机制，我们模拟了具有不同抑制性输入分布模式的运动单位池的行为。我们的模拟支持这样一种假设，即抑制性输入的非均匀分布（并非严格按照运动单位大小组织）是中等收缩强度下对伤害性刺激的运动反应的关键机制。要点：疼痛影响运动，但这些运动适应性背后的神经机制尚未明确界定。传统观点认为疼痛会导致运动单位之间均匀（同质）的抑制。最近的研究观察到运动单位对实验性疼痛有不同反应——一些放电率降低，另一些放电率增加。将实验数据与建模相结合，我们提供了令人信服的证据，表明抑制增加且在运动单位间分布不均匀，无论其大小如何。
