Effects of Mental Fatigue and Monetary Incentives on Exercise Intensity Decision-Making and Performance

Mental fatigue affects choice between exercise and nonexercise tasks. Provision of financial or monetary incentives biases decision-making in favor of exercise behaviors. The present study examined the effects of mental fatigue and monetary incentives on exercise intensity decision-making and physical performance. Using a 2 [higher fatigue (HF) vs. lower fatigue (LF)] × 2 [incentive ($) vs. no incentive] between-groups design, recreationally active participants (N = 77, Mage = 20.14 ± 2.16 years) completed a 12-min manipulation designed to create higher and lower levels of mental fatigue and then chose between moderate-intensity and vigorous-intensity exercise protocols. Participants in the incentive groups were offered $2.00 CAD or $4.00 CAD for the moderate or vigorous-intensity options, respectively, and participants were required to perform their chosen exercise task. Mental fatigue in the HF groups was significantly higher than the LF groups. Analyses revealed an overall greater frequency of selecting vigorous-intensity versus moderate-intensity exercise with no difference in choice frequency between the HF and LF groups. Paired comparisons showed a significantly greater frequency of selecting the vigorous-intensity option in the LF$ group compared to the LF group, and a nonsignificant, medium-sized effect showing a slight bias toward the vigorous-intensity option for people in the HF$ group compared to the LF group. No differences were observed between groups in physical work performed during exercise. Findings suggest a disproportionate influence of incentives over mental fatigue on exercise intensity decision-making and no effect of mental fatigue on self-selected, self-paced exercise.