Surface EMG (sEMG) has been used to compare loading conditions during exercise. Studies often explore mean/median frequencies. This potentially misses more nuanced electrophysiological differences between exercise tasks. Therefore, wavelet-based analysis was used to evaluate electrophysiological characteristics in the sEMG signal of the quadriceps under both higher- and lower-torque (70 % and 30 % of MVC, respectively) isometric knee extension performed to momentary failure. Ten recreationally active adult males with previous resistance training experience were recruited. Using a within-session, repeated-measures, randomised crossover design, participants performed isometric knee extension whilst sEMG was collected from the vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL). Mean signal frequency showed similar characteristics in each condition at momentary failure. However, individual wavelets revealed different frequency component changes between the conditions. All frequency components increased during the low-torque condition. But low-frequency components increased, and high-frequency components decreased, in intensity throughout the high-torque condition. This resulted in convergence of the low-torque and high-torque trial wavelet characteristics towards the end of the low-torque trial. Our results demonstrate a convergence of myoelectric signal properties between low- and high-torque efforts with fatigue via divergent signal adaptations. Further work should disentangle factors influencing frequency characteristics during exercise tasks.

表面肌电图 (sEMG) 已用于比较运动期间的负荷条件。研究经常探索平均/中值频率。这可能会忽略运动任务之间更细微的电生理差异。因此，使用基于小波的分析来评估股四头肌在较高扭矩和较低扭矩（分别为 MVC 的 70% 和 30%）等长膝关节伸展至瞬时衰竭时股四头肌 sEMG 信号的电生理学特征。招募了十名具有抗阻训练经验的休闲活跃的成年男性。采用会话内重复测量、随机交叉设计，参与者进行等长膝关节伸展，同时从股内侧肌 (VM)、股直肌 (RF) 和股外侧肌 (VL) 收集 sEMG。在瞬时故障的每种情况下，平均信号频率都表现出相似的特征。然而，各个小波揭示了不同条件下不同频率分量的变化。所有频率分量在低扭矩条件下均增加。但在整个高扭矩条件下，低频成分的强度增加，而高频成分的强度降低。这导致低扭矩和高扭矩试验小波特性在低扭矩试验结束时收敛。我们的结果表明，通过不同的信号适应，低扭矩和高扭矩努力与疲劳之间的肌电信号特性趋于一致。进一步的工作应该理清影响运动任务期间频率特性的因素。