The waning willpower: A highly powered longitudinal study investigating fatigue vulnerability and its relation to...

Research has shown that current mental fatigue and self-control capacity play a crucial role in the goal-directed regulation of emotion, motivation, and cognition. However, we still do not fully understand if the emergence of fatigue during the exercise of cognitive performance indicates a person's trait fatigue vulnerability. In this longitudinal study, we repeatedly measured the self-reported perceived control capacity of N = 2,094 trainees over the course of three separate, 140-min-long standardized achievement tests in mathematics and science. These tests were administered at the beginning of trainees' vocational education, prior to their intermediate exams, and before their final exams. In all three testing sessions, participants' control capacity declined over time, which indicated increasing mental fatigue. The intercepts and slopes of three latent growth curves loaded on two higher order trait factors, representing individual differences in (a) individuals' stable pretask control capacity (control preparedness) and (b) changes in control capacity over time (fatigue resistance). Further, we examined the relationships of both fatigue trait factors and self-reported personality traits, as well as objectively assessed fluid intelligence and general achievement test performances. The strongest predictors of control preparedness were conscientiousness, neuroticism, and fluid intelligence, whereas fatigue resistance was predicted exclusively by neuroticism and conscientiousness. Individuals with higher levels of control preparedness tended to outperform others in achievement testing. Our findings underscore the importance of repeatedly tracking control capacity within and across achievement tests to better understand individual differences in fatigue-related traits, their associations with stable personal characteristics, and their impact on cognitive performance in real-life settings. (PsycInfo Database Record (c) 2025 APA, all rights reserved).