The Effect of Mental Fatigue on Half-Marathon Performance: a Pragmatic Trial

Abstract Purpose It is well established that mental fatigue impairs performance during lab-based endurance tests lasting < 45 min. However, the effects of mental fatigue on longer-duration endurance events and in field settings are unknown. The aim of this study was to investigate the effect of mental fatigue on performance during a half-marathon race.Methods Forty-six male amateur runners (means ± SD: age 43.8 ± 8.6 years, V̇O2max 46.0 ± 4.1 ml/kg/min) completed an half-marathon after being randomly allocated to performing a 50-min mentally-fatiguing task (mental fatigue group) or reading magazines for 50 min (control group). Running speed, heart rate, and perceived effort were measured during the race.Results The mental fatigue group completed the half-marathon approximately four minutes slower (106.2 ± 12.4 min) than the control group (102.4 ± 10.2 min), but this difference was not statistically significant (Cohen’s d = 0.333; p = 0.265). However, equivalence was not established (t(40.88) = 0.239, p = 0.594) and equivalence testing analysis excluded a worthwhile positive effect of mental fatigue on half-marathon performance.Conclusion Due to its posttest-only design and the achievable sample size, the study did not have enough power to provide evidence that the observed 4-minute increase in half-marathon time is statistically significant. However, equivalence testing suggests that mental fatigue has no beneficial effects on half-marathon performance in male amateur runners, and harmful effects cannot be excluded. Overall, it seems prudent for endurance athletes to avoid mentally-fatiguing tasks before competitions.