Mental Fatigue, Motivation, and Physical Activity Decision-Making

Abstract

Previous research has demonstrated mental fatigue impairs subsequent physical performance, however, current understanding of the role of mental fatigue on physical activity and exercise decision-making is limited for several reasons. For example, research examining the relation between mental fatigue and physical activity behaviors has relied on experimental methods and physical tasks performed in controlled laboratory settings with limited applicability to everyday experiences. In addition, direct measures of motivation commonly used within the literature are subject to biases, highlighting the importance of alternate methods for assessing motivation using indirect measures. To address these limitations, methods with stronger ecological validity are needed to extend research from controlled, experimental settings to measure mental fatigue in naturalistic settings and provide a diverse range of physical activity and exercise task options. The purpose of this dissertation is to investigate the associations between mental fatigue, motivation, and physical activity behavior to further our understanding of the decision- processes behind choosing to engage or not engage in physical activity. Study 1 examined the effects of mental fatigue on the decision to engage in an acute bout of moderate-to-vigorous intensity physical activity or a competing sedentary alternative using a mixed-methods study design. Results showed a sequential mediation effect of mental fatigue on choice through subjective perceptions of effort, benefits, and costs. Results of qualitative analyses highlight individual-level consequences of completing cognitively demanding and non-demanding tasks on physical activity decision-making. Findings are consistent with previous research and demonstrate subjective perceptions of engaging in physical activity account for acute choice. Study 2 investigated the effects of intensity and duration on people’s subjective valuations of physical activity tasks using an effort discounting paradigm and the potential moderating effect of mental fatigue on subjective valuations of physical activity. Results showed a reduced willingness to engage in physical activities of higher intensities and longer durations. Further, there was partial evidence suggesting a reduced willingness to engage in vigorous-intensity physical activity with higher levels of mental fatigue. Findings provide novel insight towards factors influencing people’s motivation for engaging in physical activity with some evidence that mental fatigue affects people’s motivation to exert physical effort. Study 3 examined the association between mental fatigue, subjective evaluations of perceived benefits and costs, and moderate-to-vigorous intensity physical activity using ecological momentary assessment and accelerometry. Results demonstrate significant associations between all study variables. Although a multilevel mediation model was not significant, evidence supports a partial mediation effect attributable to benefit vs. cost valuation on the relation between mental fatigue and physical activity. Results provide insight into real-time predictors of motivation and physical activity, highlighting the complex relationships between psychological variables and behavior in people’s everyday decision making.