The Waning Willpower: A Highly Powered Longitudinal Study Investigating Fatigue Vulnerability and Its Relation to Personality, Intelligence, and Cognitive Performance

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, whether the emergence of fatigue during the exercise of cognitive performance is indicative of individuals’ time-invariant fatigue vulnerability traits is still not well understood. In this longitudinal study, we repeatedly measured the perceived control capacity of N = 2094 trainees over the course of working on three separate, 140-minute-long standardized achievement tests in mathematics and science. These tests were administered at the beginning of trainees’ vocational education and training, 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 fatigue vulnerability trait factors representing the interindividual variabilities in individuals’ stable aspects of pre-task control capacity (control preparedness) and its change over time (fatigue proneness). Further, we examined the relations of both fatigue trait factors to personality, intelligence, and individuals’ general achievement test performances. The strongest predictors of control preparedness were conscientiousness, neuroticism, and fluid intelligence, whereas fatigue proneness was predicted exclusively by neuroticism and conscientiousness. Individuals with higher levels in control preparedness tended to outperform others in achievement testing. Post-hoc power analyses provide evidence for the high statistical power of the results. We discuss theoretical and practical implications for personality research on mental fatigue effects in performance situations.