Testing the Strength Model of Self-Control: Does Willpower Resemble a Muscle? CHRISTOPHER L. FULLERTON BSc A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy November 2016 This work or any part thereof has not previously been presented in any form to the University or to any other body whether for the purposes of assessment, publication or for any other purpose (unless otherwise indicated). Save for any express acknowledgments, references and/or bibliographies cited in the work, I confirm that the intellectual content of the work is the result of my own efforts and of no other person. The right of Christopher Fullerton to be identified as author of this work is asserted in accordance with ss.77 and 78 of the Copyright, Designs and Patents Act 1988. At this date copyright is owned by the author. Signature……………………………………….. Date…………………………………………….. I Abstract The strength model of self-control predicts that when people exert self-control, they should show performance decrements on subsequent self-control tasks. However, it is possible that this pattern of behaviour is confined to specific experimental procedures, which amplifies the effect. The aims of this thesis are to; 1) test the strength model predictions in sport; and 2) examine emotion as a mediator of self-control performance effects. Study 1 consisted of two experiments. Experiment 1 set out to demonstrate a pattern of resource depletion. Forty-three sport and exercise students performed either an incongruent (self-control depletion) or congruent (control) Stroop task before and after performing a virtual reality cycling task on an indoor cycling ergometer. Findings showed the depletion group performed worse on the second Stroop task than on their first task or than the control group. Experiment 2 sought to address some of the methodological concerns in Experiment 1, and examine emotion as a factor explaining performance. Forty- eight physically active participants followed the same experimental protocol, but with an additional iteration of both tasks. Results demonstrated that both cycling and Stroop task performance improved across time. In addition, participants reported feeling happier and more motivated during the second cycling task. Study 2 provided a conceptual replication of Study 1, using different tests of self- control. Twenty-six university-level male soccer players either performed the Loughborough Soccer Passing Test (LSPT) with (self-control depletion) or without (control) an audio file simulating crowd noise, and then performed the wall squat muscle endurance test. The self-control depletion group reported feeling more anxious during the LSPT and performed worse than the controls on the wall squat. II Next, in Study 3, nineteen well-trained competitive endurance runners performed a self-paced 1600 m running trial and then ran a second trial either self-paced or with a pacemaker. The pacemaker had no significant effect on actual performance time but participants reported feeling more anxious beforehand and adopted a fast start strategy, whereas the self-paced group had a conservative pacing pattern. Study 4 showed that, for females, consuming a sports drink—as opposed to plain water—associated with better physical (high-intensity track running) and cognitive self-control (Stroop) performance. In addition, they appeared to be happier drinking water, and more anxious drinking the sports drink—an effect that diverged over the six weeks. Study 5 examined the effects of three strategies—designed to increase or decrease the intensity of emotions—on emotion, pacing strategy and 1600 m performance. Results showed the intervention designed to decrease unpleasant emotions was associated with lower anxiety, higher calmness, a slower first 400 m, and more overall consistent pacing strategy. Study 6 examined the effects of imagery training on swimming tumble-turn performance. Findings showed no significant intervention effect, a result that goes against the proposed benefits of psychological skills training and runs counter to the predictions of the strength model. Collectively, the evidence in the thesis provides limited support for the strength model. It is concluded that self-control performance does not inevitably deteriorate across self-control tasks where the individual is well-versed with the task demands, or where tasks are not physically strenuous enough to tax mental resources. In contrast, the explanation for performance deterioration across a series of novel tasks is likely to extend beyond that of a self-control resources perspective. Future research might profitably test this proposal. III Acknowledgments I often wonder how I ended up at this point: I dropped psychology as an A-Level subject, and wanted to be an artist. Yet here I am putting the finishing touches to a thesis in Sport and Exercise Psychology. And so I would like to thank those who started me on this journey, but most importantly, those who ensured that I got this thesis written. The ironic thing about studying self-control is that one invariably ends up procrastinating…a lot! Perhaps unsurprisingly, then, I also found it quite hard to counter the habit. Which brings me to thank Professor Andy Lane for never allowing the deadline to run away from me. Thanks, also, for being downright good fun to work with. I’m not sure many PhD students cycle to conferences with their supervisor or sign up to a marathon within a few months of starting! I would also like to acknowledge and express my appreciation to Dr Tracey Devonport. Tracey; along with Andy, you supported my development as a researcher, and offered opportunities to apply theory in real-world contexts. I have you to thank for introducing me to Ron Allan at Tipton Tennis Academy. Working with the players, coaches and parents there during my final year was a definite highlight of the PhD. Like Andy, your supervision, friendship, guidance and support is truly valued. I genuinely feel excited and confident that this experience will serve me well in all my future endeavours. I would like to thank Dr Lee Crust, Dr Richard Keegan and Simon George who, each in differing ways, introduced me to the possibility of studying for a PhD. I certainly would not be where I am now without your encouragement and help. IV And finally, I must thank my family—you have been an ongoing source of support. Not once did I feel as though the PhD was unattainable. Challenging, yes; but not abstract. You ensured I maintained perspective throughout and embraced the PhD journey. V Contents Abstract ............................................................................................................................. II Acknowledgments........................................................................................................... IV List of Tables ................................................................................................................. XII List of Figures ............................................................................................................... XIII Publications .................................................................................................................. XIV Chapter 1: Introduction ...................................................................................................... 1 1.1 Background .............................................................................................................. 1 1.2 Overview of Current Research Programme ............................................................. 4 Chapter 2: Review of Literature ........................................................................................ 9 2.1 Abstract ........................................................................................................................ 9 2.2 Introduction ................................................................................................................ 10 2.2.1 Definitions........................................................................................................... 11 2.3 The Strength Model of Self-Control .......................................................................... 12 2.3.1 The Ego Depletion Effect ............................................................................... 13 2.3.2 Conserving Self-Control Strength................................................................... 18 2.3.3 Does Self-Control Rely on Glucose? .............................................................. 21 2.3.4 Recovery of Self-Control Resource ................................................................ 26 2.3.5 Restoring Self-Control Strength ..................................................................... 27 2.3.6 Self-Control Training ...................................................................................... 31 2.3.7 Individual Differences in Self-Control ........................................................... 34 2.4 Alternative Models..................................................................................................... 39 VI 2.4.1 The Resource Allocation Model of Self-Control ................................................ 39 2.4.2 Implicit Theories about Self-Control .................................................................. 44 2.5 General Discussion .................................................................................................... 47 2.5.1 Concluding Remarks ..........................................................................................