Fatigue-Induced Neuromuscular Responses Differ Between Endurance- and Strength-Trained Males

This study aimed to investigate the effect of training background on neuromuscular responses to submaximal isometric fatiguing contraction. Eleven strength-trained (ST) and 11 endurance-trained (ET) males performed maximal voluntary isometric knee extension contractions (MVIC) and a torque steadiness task at 20% MVIC before and immediately after a submaximal isometric contraction at 30% MVIC performed until task failure. High-density surface EMG was recorded from the vastus lateralis muscle. The EMG root mean square (RMS) amplitude, median frequency (MDF) and muscle fibre conduction velocity (MFCV) were estimated. There was no significant difference in time-to-failure (88.2 ± 34.3 vs. 157.6 ± 126.1 s) or post-fatigue MVIC reduction (19.4% vs. 22.5%) between the ST and ET groups. However, post-fatigue EMG MDF decreased by 10.8% in ST (p < 0.05), but remained unchanged in ET. Furthermore, only the ET group showed a significant decrease in torque steadiness (p < 0.05) and an increase in physiological tremor (8-12 Hz; p < 0.01) during the post-fatigue steadiness task. Throughout the fatiguing task, the mixed effects model revealed decreases in MFCV (p < 0.01) and MDF% (p < 0.001) in ST, with no differences observed in the ET group. EMG RMS amplitude increased similarly in both groups during the fatiguing contraction (p < 0.001). Fatiguing exercise induced comparable reductions in MVIC in ST and ET males. However, fatigue differentially affected the neuromuscular strategies adopted by each group when generating maximal strength and maintaining submaximal torque output, possibly reflecting differences in muscle fibre distribution between the two groups.