| Summary: | The placebo effect is arguably accounted for in sport science research by the convention of the placebo-controlled trial. However, little research has sought to quantify or explain the effect itself. This thesis examines the placebo and pharmacological effects of caffeine in cycling performance using a multi-method approach. Methods: Extensive piloting was conducted to establish the suitability of caffeine as a vehicle for investigation, the efficacy of substance administration procedures, and the reliability of the cycle protocol. An experimental deceptive administration protocol (the balanced placebo design) was subsequently employed to quantify the relative contributions of psychology and pharmacology to the response to ingested caffeine and placebo in 14 well-trained cyclists, whilst semi-structured interviews were employed to corroborate and explicate the nature of observed effects. Finally, psychometric methods were used to identify any associations between placebo responsiveness and personality. Results: Caffeine ingestion enhanced cyclists' performance by 2.6% (95% CI 0.9-4.3, P = .002) whether they believed caffeine to have been ingested or not. No significant placebo effects were observed (1.2%, 95% CI -0.3- 2.8, P = .31), however, individual placebo responses were evident. Interview data revealed that observed placebo effects reflected both direct effects of belief on performance, and indirect effects, mediated by psychological changes and pacing decisions. Perceptions of enhanced performance were not always reflected in overt performance, raising the question as to what exactly constitutes a placebo effect. Synthesis of data suggest that certain personality traits such as Openness to experience and Neuroticism may relate to placebo responding. Conclusions: Caffeine ingestion may enhance the performance of a well-trained cyclist independently of their beliefs as to whether caffeine has been ingested or not. The belief that caffeine has been ingested might elicit a performance enhancing effect in certain placebo responsive individuals. Implications for placebo effect research and sports performance research and practice are discussed alongside directions for further research
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