Gomes João Sá, Oliveira João Henriques, Bauer Philipp, Pezarat-Correia Pedro, Vaz João R
Egas Moniz Center for Interdisciplinary Research (CiiEM), Egas Moniz School of Health and Science, Quinta da Granja, 2829-511, Monte da Caparica, Portugal.
Neuromuscular Research Laboratory, Faculty of Human Kinetics, University of Lisbon, Lisbon, Portugal.
Sci Rep. 2025 Apr 15;15(1):12881. doi: 10.1038/s41598-025-96102-7.
Physiological complexity is believed to reflect a system's adaptability to environmental challenges having been proposed as an indirect indicator of the functional capacity of the neuromuscular system. This study aimed to investigate the association between torque complexity's changes with neuromuscular fatigue and motor unit parameters. Twenty-one healthy and young adults visited the laboratory on one occasion. Knee extension maximum voluntary isometric contractions and isometric contractions at 30% of maximum were collected at baseline and immediately after a fatiguing knee extension protocol, which consisted of a series of concentric and eccentric knee extensions at 90°/s until exhaustion. Torque signals were sampled continuously, and torque complexity was assessed through an entropy measure. Motor unit-related parameters were extracted from the submaximal trials and further analysed. Our findings demonstrate that torque complexity's alteration pre-to-post neuromuscular fatigue is highly correlated with vastus lateralis and medialis average firing rate (r = - 0.618 and r = - 0.659, respectively) and peak motor unit action potential amplitude (r = - 0.801 and r = - 0.703, respectively) pre-fatigue. Moreover, alterations in torque complexity were observed, indicating a loss of adaptability within the neuromuscular system with neuromuscular fatigue. Overall, our findings supported our hypothesis by demonstrating alterations in torque complexity with neuromuscular fatigue, rendering the system less adaptable. Moreover, our results added to the current knowledge by highlighting the association between torque complexity's changes with neuromuscular fatigue and motor unit parameters.
生理复杂性被认为反映了系统对环境挑战的适应性，已被提议作为神经肌肉系统功能能力的间接指标。本研究旨在探讨扭矩复杂性变化与神经肌肉疲劳及运动单位参数之间的关联。21名健康的年轻成年人到实验室进行了一次测试。在基线时以及在进行疲劳性膝关节伸展方案后立即采集了膝关节伸展最大自主等长收缩和最大收缩力30%时的等长收缩，该疲劳性膝关节伸展方案包括一系列以90°/秒进行的向心和离心膝关节伸展，直至力竭。连续采集扭矩信号，并通过熵测度评估扭矩复杂性。从次最大收缩试验中提取与运动单位相关的参数并进行进一步分析。我们的研究结果表明，神经肌肉疲劳前后扭矩复杂性的变化与股外侧肌和股内侧肌的平均放电率（分别为r = -0.618和r = -0.659）以及疲劳前运动单位动作电位峰值幅度（分别为r = -0.801和r = -0.703）高度相关。此外，观察到扭矩复杂性的变化，表明神经肌肉系统随着神经肌肉疲劳而失去适应性。总体而言，我们的研究结果通过证明神经肌肉疲劳时扭矩复杂性的变化支持了我们的假设，使系统适应性降低。此外，我们的结果通过强调扭矩复杂性变化与神经肌肉疲劳和运动单位参数之间的关联，丰富了当前的知识。
