Exploratory study of electromyographic behavior of the vastus medialis and vastus lateralis at neuromuscular fatigue onset

This study aimed to determine and analyze the neuromuscular fatigue onset by median frequency (MDF) and the root mean square (RMS) behavior of an electromyographic signal (EMG). Eighteen healthy men with no prior knee problems initially performed three maximum voluntary isometric contractions (MVIC). After two days of MVIC test, participants performed a fatiguing protocol in which they performed submaximal knee-extension contractions at 20% and 70% MVIC held to exhaustion. The MDF and RMS values from the EMG signals were recorded from the vastus medialis (VM) and the vastus lateralis (VL). Analysis of the MDF and RMS behavior enabled identification of neuromuscular fatigue onset for VM and VL muscles in 20% and 70% loads. Alterations between the VM and VL in the neuromuscular fatigue onset, at 20% and 70% MVIC, were not significant. These findings suggest that the methodology proposal was capable of indicating minute differences sensible to alterations in the EMG signals, allowing identification of the moment when the MDF and the RMS showed significant changes in behavior. The methodology used was also a viable one for describing and identifying the neuromuscular fatigue onset by means of the analysis of EMG signals.

本研究旨在通过中值频率（median frequency, MDF）与肌电信号（electromyographic signal, EMG）的均方根（root mean square, RMS）特征，确定并分析神经肌肉疲劳起始点。招募18名无既往膝关节病史的健康男性受试者，初始完成3次最大自主等长收缩（maximum voluntary isometric contractions, MVIC）测试。间隔2天后，受试者执行疲劳负荷方案：分别以20%与70%MVIC的强度维持膝关节伸展收缩至力竭。研究从股内侧肌（vastus medialis, VM）与股外侧肌（vastus lateralis, VL）采集EMG信号，并计算其MDF与RMS值。通过分析MDF与RMS的变化特征，可识别20%与70%负荷下股内侧肌及股外侧肌的神经肌肉疲劳起始点。在20%与70%MVIC负荷条件下，股内侧肌与股外侧肌的神经肌肉疲劳起始点差异无统计学意义。本研究结果表明，所提出的方法能够敏锐捕捉EMG信号的细微变化，可精准识别MDF与RMS行为发生显著改变的时刻。该方法同样可作为一种可靠手段，通过分析EMG信号描述并识别神经肌肉疲劳起始点。