Does mental fatigue impair physical performance? A replication study.

The aim of this study is to replicate the hypothesis that mental fatigue impairs physical performance in a pre-registered (https://osf.io/wqkap/) within-subjects experiment. 30 recreationally active adults completed a time-to-exhaustion test (TTE) at 80% VOmax in two separate sessions, after completing a mental fatigue task or watching a documentary for 90 min. We measured power output, heart rate, (session) rating of perceived exertion (RPE) and subjective mental fatigue. Bayes factor analyses revealed extreme evidence supporting the alternative hypothesis that the mental fatigue task was more mentally fatiguing than the control task, BF = 0.009. However, we found moderate-to-strong evidence for the null hypothesis (i.e., no evidence of reduced performance) for average time in TTE (BF = 9.762) and anecdotal evidence for the null hypothesis in (session) RPE (BF = 2.902) and heart rate (BF = 2.587). Our data seem to challenge the idea that mental fatigue has a negative influence on exercise performance. Although we did succeed at manipulating subjective mental fatigue, this did not impair physical performance. However, we cannot discard the possibility that mental fatigue may have a negative influence under conditions not explored here, e.g., individualizing mentally fatiguing tasks. In sum, further research is warranted to determine the role of mental fatigue on exercise and sport performance.