Author(s): HABAY, J., DE PAUW K., PATTYN N., VAN CUTSEM J., ROELANDS B., Institution: VUB, Country: BELGIUM, Abstract-ID: 2158

INTRODUCTION:
Mental fatigue (MF) negatively impacts human performance. Recent studies suggest substantial interindividual variability in MF response, complicating interpretation of effects, mechanisms and management [1,2]. Yet, this is based solely on observational evidence. Moreover, while some studies have assessed the origin of this variability using features such as age, no investigation has yet assessed the combined influence of multiple internal variables. We therefore investigated the range, origin, and temporal robustness of individual MF responses.
METHODS:
Ninety-eight healthy subjects (33 ± 9y, 44F) completed a randomized crossover trial with familiarization, intervention and control sessions. During familiarization, 19 individual features were collected, including anthropometric (e.g., age), physical (e.g., VO₂max), cognitive (e.g., attention) and psychological (e.g., anxiety) variables. MF was induced using a 45min Stroop task; a 45min documentary served as control. Dependent variables included the MF visual analogue scale (MVAS) and GoNoGo reaction time (RT) measured pre- and post-intervention/control task, and the total distance and rate of perceived exertion (RPE) during a subsequent time trial (TT). The range of the interindividual variability was assessed using standard deviations of individual response (SDIR) and Pitman Morgan tests. Feature effects were tested using moderation analyses. Temporal robustness was assessed in 25 subjects (31 ± 8y, 10F) with an identical one year follow-up using mixed linear models and intraclass correlation coefficients (ICC).
RESULTS:
The SDIR indicated variability for all outcomes, but only the GoNoGo RT Pitman-Morgan test reached significance (t(98)=0.38;p<0.001). Moderation analyses revealed that baseline physical activity (p=0.033) and self-control (p=0.027) attenuated the effect of MF on TT distance. Effects on RPE were moderated by response inhibition (p=0.041), physical activity (p=0.023) and sport level (p=0.012). None of the remaining 14 features influenced the MF effect on these variables, nor did any features influence MF effects on MVAS or GoNoGo RT. Comparison from baseline to follow up revealed a small decrease in MF effect on TT distance and RPE. Only TT distance showed significant temporal robustness (ICC=0.448, p=0.011).
CONCLUSION:
This is the first large-scale investigation of interindividual variability in MF response. Our analyses indicated a limited amount of true variability, with a minimal influence of individual features. This indicates, together with the low temporal robustness, that the response to MF should be seen as a varying and externally influenced state, as opposed to a stable trait. This has major implications for research and practice, requiring revisions of theoretical models, management guidelines, and prior interpretations, while redirecting attention toward external influences of MF.
1.Habay, J., et al., Sports Medicine - Open, 2023. (PMID: 36808018)
2.Habay, J., et al., MSSE, 2025 (PMID: 40938104)