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Exerting cognitive control can lead to mental fatigue and impair self-regulation of subsequent physical performance. However, current understanding is limited due to a number of factors. First, studies have employed manipulations involving either high or low cognitive demands, failing to test whether a dose-response relationship exists between mental fatigue and physical performance. Second, the role of several psychological variables among the mental fatigue – physical performance relationship remains unclear. Third, current literature lacks generalizability in that existing findings have largely been derived from studies involving active samples performing physical tasks that the general population may not commonly engage in for health and fitness benefits. Lastly, there has been little research examining intervention strategies that may attenuate the effects of mental fatigue on physical activity behaviour. This dissertation aimed to advance our understanding of self-regulation of physical activity behaviour in response to mental fatigue by addressing shortcomings within the literature discussed above. Study 1 examined whether a dose-response relationship exists for mental fatigue and physical performance. Results showed a performance threshold exists between 4 and 6 minutes of exposure to a mentally fatiguing cognitive control task. Beyond this threshold, task self-efficacy also showed uniform reductions which mediated the mental fatigue – physical performance change relationship. Findings are consistent with previous research and reveal self-efficacy is a key variable that accounts for the negative effects of mental fatigue on physical performance. Study 2 investigated the hypothesis that offering a performance contingent monetary incentive would attenuate the negative carryover effects of mental fatigue on physical performance. Findings showed mental fatigue caused characteristic declines in physical performance; however, incentives countered the effects of mental fatigue and led to performances equal to those witnessed in a non-fatigued state. Interestingly, incentives did not provide any additional benefit for performance when not fatigued. Findings support motivational accounts of self-regulation, although incentives may lack practicality and may not be a cost-effective means to alter exercise behaviour. Study 3 examined the effect of mental fatigue on intended physical exertion and exercise performance reflective of current public health guidelines for physical activity in a sample comprised of insufficiently active university students. Findings showed mental fatigue alters the amount of physical effort people are willing to invest in an exercise workout and follow through with those intentions by doing less work and exercising at a lower heart rate intensity. These are the first results showing people may deliberately adjust their physical effort to cope with mental fatigue. Study 4 investigated whether heart rate biofeedback moderates the effects of mental fatigue on vigorous-intensity exercise reflective of current public health physical activity guidelines and the effects of mental fatigue on pre-exercise motivational cognitions. Results showed mental fatigue was associated with decreases in intended physical effort and commitment to vigorous-intensity exercise goals which corresponded with reductions in exercise intensity (i.e., HRAVE) and total work performed when people exercised without feedback. However, HR biofeedback attenuated the negative carryover effects of mental fatigue on exercise behaviour, restoring exercise intensity and performance to levels witnessed in a non-fatigued state. Similar to incentives, biofeedback offered no further benefits for performance when not fatigued. Findings align with predictions of Control Theory and suggest biofeedback using widely available physical activity monitors in combination with goals can improve intensity-based physical activity guideline adherence when confronted with barriers such as mental fatigue. / Thesis / Doctor of Philosophy (PhD) / Effortful cognitive control exertion can lead to mental fatigue and impair self-regulation of subsequent physical performance. However, current understanding is limited due to a number of factors. This thesis addressed several gaps in the literature through a systematic examination of potential mediators and moderators of the mental fatigue - physical performance relationship. Findings revealed downstream physical performance impairments are dependent on exceeding a critical mental fatigue threshold. Reductions in pre-exercise cognitions including self-efficacy, intended physical exertion and goal commitment all correspond with negative changes in exercise performance. Evidence also highlights the generalizability of fatigue-induced effects by demonstrating that insufficiently active people engaging in exercise for health and fitness benefits down-regulate exercise performance in the face of mental fatigue. Incentives and heart rate biofeedback can attenuate the effects of mental fatigue on physical performance. Collectively, evidence provides insight for theories of self-control and can be interpreted within Muller and Apps (2018) neurocognitive framework of motivational fatigue.

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A strategy for facilitating post-treatment weight maintenance was examined. Subjects were matched for age, sex, and amount of weight that they desired to lose and were then assigned to one of two groups. Both groups were under contracts and had individually designed self-control programs for weight loss, but subjects in the experimental group lost weight in small steps and subjects in the control group lost weight continuously. The experimental group was predicted to have better weight maintenance after treatment because of a greater number of reinforcements for weight loss. Two-month follow-up data was obtained on the ten subjects who completed the study, and the experimental group was found to have regained significantly less than the control group after treatment ended. The implications of these results for obesity research are discussed.

In this thesis, I take a mixed methods approach to exploring motivations and explanations for self-control and self-control failure. In Study 1, I used quantitative, experimental methods to test predictions derived from the strength model of self-control and self-determination theory related to voluntary risk, vitality, and self-control. In Study 2, I used thematic analysis of qualitative interviews to describe how people experience self-control and self-control failure. The strength model describes self-control as a limited resource that is depleted by acts requiring executive control. When people’s self-control is depleted, they are motivated to conserve and replenish self-control resources. One way of regaining self-control may be engaging in risky activities that provide a replenishing sense of vitality. Feelings of vitality are associated with perceptions of autonomy, and may serve as an experiential barometer of self-control strength. In Study 1, I manipulated self-control depletion and risk autonomy to test whether people engage in risky choices to provide a replenishing sense of vitality. My results suggest that vitality is not a reliable barometer of self-control strength. Perceptions of autonomy appear to be a predictor of short-term self-control strength, such that forced risk is a depleting experience. Further, perceptions of autonomy were an important facet of participants’ attributions of self-control success. However, thematic analysis further suggests that experiences of self-control cannot be removed from a context of motivation and emotion. More than just short-term fluctuations in ability to resist temptation, people’s personal theories of self-control provide a long-term narrative for explaining success and failures of goal-directed striving. More than just an intra-individual construct, the social context of self-control appears to have important influences on people’s attributions for self-control and self-control failure. By combining quantitative and qualitative methods, I add to the self-control literature by providing an account of the mechanisms and experiences of self-control and self-control failure.

Given increasing interest in the therapeutic benefits of mindfulness, limitations of its treatment utility are frequently questioned. As such, the purpose of the study was to examine the effects of mindfulness on a subsequent self-control task in a sample of college students. A total of 67 participants were randomly assigned to one of three conditions: a control condition, an experimental mindfulness-only condition or a comparison expectancy-plus-mindfulness condition to investigate the utility of mindfulness practice when motivated by an outcome of increased self-control. Results did not indicate a difference in persistence on a difficult task between conditions, regardless of the manipulation. Conceptual and experimental limitations of current study’s findings, as well as future directions, are discussed.

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The present study was concerned with investigating children's generalized locus of control of reinforcement and its possible relationship to the demographic variables of birth order and family size. The sample consisted of 93 school children in Grades 6, 7, and 8. The analysis of data was by a 2 x 3 factorial design. Results indicated no significant differences in the generalized locus of control orientations of first-born, intermediate-born, and youngest children. Results also indicated that children of these different birth order positions from small families and from large families did not differ significantly in their generalized locus of control orientation. A correlational study of the data showed that the children's locus of control orientations were unrelated to sex differences.