Mindfulness and acceptance approaches to athletic performance

Performance enhancement strategies in sport have frequently attempted to help athletes gain control over their thoughts and their emotions (Vealey, 1994) . These are 'content-focused' approaches try to change the content of the athlete's internal experience. Recently, increasing attention has been directed toward interventions that try to change an athlete's relationship with those internal experiences, instead of changing the content. These 'context-focused' approaches-including mindfulness and acceptance-based interventions - aim to help athletes perform well with anxiety, rather than trying to remove the anxiety (Gardner & Moore, 2012b) . These approaches promote similar acceptance of other unhelpful cognitions and emotions, such as anger or self-doubt. In this thesis, I aimed to explore the effectiveness of these approaches for promoting performance in sport.

Chapter 1 identified the theories underlying context-focused approaches and outlined how they might reduce the likelihood of performance problems. For example, due to decreased self-focused attention, context-focused approaches may reduce the likelihood of choking due to explicit control of otherwise automatic skills. To see how well these theories held up to empirical exploration, Chapter 2 systematically reviewed the literature on context-focused approaches in sport. This review included prototypical context-focused approaches, like mindfulness, and also the wider range of approaches that operate by a similar mechanism, such as self-compassion. It found consistent trends in the research that these approaches improve athletic present-moment awareness, flow, performance, and help to reduce anxiety. It also revealed preliminary evidence for other outcomes like improved confidence and reduced rates of injury. However, none of the 66 studies met the Cochrane Collaboration criteria for low risk of bias (Higgins, Altman, Gotzsche, et al., 2011) .

In Chapter 3, I aimed to test a brief context-focused intervention using a study design that met these Cochrane criteria. Golfers were randomised into either a acceptance-based intervention or a control condition. The study was double-blinded, randomised, prospectively registered with putting performance as the primary outcome. This study found few benefits of the acceptance-based intervention for performance, anxiety, or state mindfulness. It found a significant improvement on a secondary outcome: swing mechanics as measured by a SAM PuttLab (Science & Motion, 2016) . While brief interventions are well-established for testing context-focused interventions (Levin, Hildebrandt, Lillis, & Hayes, 2012) , Chapter 3 did not find strong evidence that a brief context-focused intervention leads to short-term improvements in sport performance.

One barrier to testing interventions in sport is the questionnaire response burden placed on athletes. This is not unique to context-focused literature, because half of athletes in high-performance environments complete questionnaires every day (Taylor, Chapman, Cronin, Newton, & Gill, 2012) . However, in mindfulness and acceptance literature, reducing response burden would help researchers in many ways. Shorter measures allow researchers to assess more constructs in parallel, or assess the same construct more regularly (Basarkod, Sahdra, & Ciarrochi, 2018) . Many short measures fail to meet psychometric criteria (Smith, McCarthy, & Anderson, 2000) because the process of optimally shortening a questionnaire requires complex evaluations of many factors (Marsh, Ellis, Parada, Richards, & Heubeck, 2005) . As an alternative method, Chapter 4 demonstrated that an advanced machine learning algorithm can shorten athletic questionnaires without compromising reliability or validity. As an example of this process, the substantive-methodological synthesis presents multiple versions of the Mindfulness Inventory for sport. Although reliability was compromised when measures were very brief, shorter measures showed equivalent validity to the full measure. The resulting measures offer future researchers some alternate methods of measuring mindfulness that can be adapted to their needs. The paper also outlined ways for other researchers to efficiently shorten their own measures.

Chapter 5 describes limitations of the previous chapters, but also identifies some ways in which researchers might assess the utility of context-focused approaches in the future. Many of these approaches require that athletes make significant investments in time. The thesis concludes that, although there is evidence these approaches might have widespread benefits inside and outside sport, it is not yet clear whether they are an effective use of time for optimising athletic performance.

Alternate title- Mindfulness in sport