Background <p>Prior research has shown that mental fatigue, induced by prolonged cognitive loads, negatively impacts subjective and behavioral variables. A currently unanswered question is whether the susceptibility to mental fatigue (i.e., how much mental fatigue a person experiences and how much it affects performance) can be classified as a state or a trait characteristic, or combination of both. Therefore, a follow-up measurement of a large-scale experimental study was conducted to assess the temporal robustness of mental fatigue susceptibility.</p> Methods <p>Twenty-five participants (10♀; 31 ± 8 y) finished a familiarization, intervention (Stroop task) and control (documentary) trial on two separate occasions (i.e., baseline and follow-up) approximately one year apart. Subjective (i.e., subjective feeling of mental fatigue (MVAS) and the rating of perceived exertion (RPE)) and behavioral (i.e., GoNoGo task reaction time and distance covered during a cycling time trial) outcomes were selected for further analysis. Temporal robustness was analyzed by comparing mixed linear models between baseline and follow-up, and performing intraclass correlation coefficients (ICC) on the condition differences between baseline and follow-up.</p> Results <p>The influence of the Stroop task on the time trial performance revealed fair temporal robustness (ICC = 0.448, <i>p</i> = 0.011), while also showing a diminishing effect of mental fatigue in follow-up compared to baseline. The influence of mental fatigue on RPE values was significant at baseline (β = 2.85, <i>p</i> = 0.022), and showed a trend towards significance at follow-up (<i>β</i> = 2.22, <i>p</i> = 0.058). GoNoGo reaction time showed limited consistency between baseline and follow-up, while there was a small significant correlation after the intervention/control task for the MVAS (ICC = 0.336, <i>p</i> = 0.047). There were no other significant correlations between condition differences.</p> Conclusions <p>Our findings favor a state-like interpretation of mental fatigue susceptibility. The results highlight the importance of RPE in driving the negative influence of mental fatigue on physical performance, while also confirming the discrepancy in subjective and behavioral quantification of mental fatigue. Future research is necessary to further investigate this phenomenon, ideally focusing on the additional influence of external features such as weather and occupational cognitive demands on mental fatigue susceptibility.</p> <p><i>Trial registration</i> Clinicaltrials.gov, NCT05576935, registered 1st of July 2022, <a href="https://clinicaltrials.gov/study/NCT05576935?term=NCT05576935&amp;rank=1">https://clinicaltrials.gov/study/NCT05576935?term=NCT05576935&amp;rank=1</a></p>