Letter to the Editor regarding the article "A 4-week endurance training program improves tolerance to mental exertion in untrained individuals"

To the Editor We read with excitement the original article by Filipas et al. (2020)1 about the influence of physical training on tolerance to mental fatigue. First, we congratulate the authors for their recent work on mental fatigue, which has generated valuable discussion. In the last decade, several studies have shown that mental fatigue decreases cognitive 2 and exercise performance. 3 Thus, understanding how ergogenic interventions, individual characteristics, and strategies that might reduce mental fatigue's deleterious effects is crucial. Although we agree that the present study is relevant and the methods are well-conducted, we propose that the results may have been misinterpreted. The title and discussion state that endurance training improves tolerance to mental exertion; however, the results indicate the contrary. The rationale that an improvement in physical performance was due to increased mental fatigue tolerance without any change in cognitive or mental fatigue scores seems flawed. It is well-established in the literature that physical training alone might have caused the observed physiological adaptations responsible for improving performance. 4 For example, even in theoretical models that consider the brain the determinant factor, the periphery (e.g., cardiorespiratory fitness) plays an essential role in modulating endurance performance. According to the psychobiological theory model5 , any factor that affects the rating of perceived exertion (RPE) and motivation will, in turn, affect performance. Thus, once motivation was similar between groups, we should closely observe what caused the differences in the RPE.