Individualized Mental Fatigue Does Not Impact Neuromuscular Function and Exercise Performance

INTRODUCTION: Recent studies have questioned previous empirical evidence that mental fatigue negatively impacts physical performance. The purpose of this study was to investigate the critical role of individual differences in mental fatigue susceptibility by analyzing the neurophysiological and physical responses to an individualized mental fatigue task. METHODS: In a preregistered (https://osf.io/xc8nr/), randomized, within-participant design experiment, 22 recreational athletes completed a time to failure test at 80% of their peak power output under mental fatigue (individual mental effort) or control (low mental effort). Before and after the cognitive tasks, subjective feeling of mental fatigue, neuromuscular function of the knee extensors, and corticospinal excitability were measured. Sequential Bayesian analysis until it reached strong evidence in favor of the alternative hypothesis (BF(10) > 6) or the null hypothesis (BF(10) < 1/6) were conducted. RESULTS: The individualized mental effort task resulted in a higher subjective feeling of mental fatigue in the mental fatigue condition (0.50 (95% confidence interval (CI), 0.39–0.62)) arbitrary units compared with control (0.19 (95% CI, 0.06–0.339)) arbitrary unit. However, exercise performance was similar in both conditions (control: 410 (95% CI, 357–463) s vs mental fatigue: 422 (95% CI, 367–477) s, BF(10) = 0.15). Likewise, mental fatigue did not impair knee extensor maximal force-generating capacity (BF(10) = 0.928) and did not change the extent of fatigability or its origin after the cycling exercise. CONCLUSIONS: There is no evidence that mental fatigue adversely affects neuromuscular function or physical exercise; even if mental fatigue is individualized, computerized tasks seem not to affect physical performance.