This study presents a model-based sensitivity analysis of the strength of voluntary muscle contraction with respect to different patterns of motor unit loss. A motor unit pool model was implemented including simulation of a motor neuron pool, muscle force, and surface electromyogram (EMG) signals. Three different patterns of motor unit loss were simulated, including (1) motor unit loss restricted to the largest ones, (2) motor unit loss restricted to the smallest ones, and (3) motor unit loss without size restriction. The model outputs including muscle force amplitude, variability, and the resultant EMG-force relation were quantified under two different motor neuron firing strategies. It was found that motor unit loss restricted to the largest ones had the most dominant impact on muscle strength and significantly changed the EMG-force relation, while loss restricted to the smallest motor units had a pronounced effect on force variability. These findings provide valuable insight toward our understanding of the neurophysiological mechanisms underlying experimental observations of muscle strength, force control, and EMG-force relation in both normal and pathological conditions.

中文翻译：

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针对不同运动单位损失模式的肌肉力量和 EMG 力关系的基于模型的分析

本研究提出了一种基于模型的随意肌肉收缩强度对不同运动单位损失模式的敏感性分析。实施了运动单元池模型，包括运动神经元池、肌肉力和表面肌电图 (EMG) 信号的模拟。模拟了三种不同的运动单位损失模式，包括（1）限制在最大的运动单位损失，（2）限制在最小的运动单位损失，和（3）没有尺寸限制的运动单位损失。在两种不同的运动神经元放电策略下量化模型输出，包括肌肉力幅度、可变性和由此产生的 EMG 力关系。结果发现，仅限于最大的运动单位损失对肌肉力量的影响最大，并显着改变了 EMG 力的关系，而仅限于最小运动单位的损失对力的可变性有显着影响。这些发现为我们理解正常和病理条件下肌肉力量、力控制和 EMG-力关系的实验观察背后的神经生理机制提供了有价值的见解。