| Summary: | Research evidence highlights regular physical activity (PA) as an increasingly important factor in the prevention of a variety of chronic diseases. Consequently, encouraging people to make PA related lifestyle changes is an everyday challenge faced by health professionals in primary and secondary health care settings. Although a number of intervention strategies have been developed and implemented, research evidence presents only limited support for their efficacy. While short-term changes may be achievable using current intervention strategies, long-term change (i.e. maintenance) appears much more difficult to achieve. Although many public health interventions are developed without explicit reference to theory, evidence suggests that the explicit use of theory will significantly improve the chances of effectiveness (Nutbeam & Harris, 2004). As no existing theoretical models are specifically intended to account for PA behaviour change, a number of pre-existing theoretical frameworks have been adopted to explain PA participation. This thesis reviews the existing body of theoretical literature in exercise psychology alongside conducting a systematic review (Study 1) of interventions based on the Transtheoretical Model (TTM). As a result, the theoretical depth or explanatory quality of existing models and theories is called into question, when applied to a PA context and specific phenomena such as long-term PA behaviour change. After reflecting on the debate surrounding different epistemological viewpoints and theoretical perspectives, applications of an alternative theory generating research approach (the Grounded Theory Methodology: GTM) are explored and evaluated. As a result, in light of the considerable epistemological debate that surrounds GTM, study 2 of this thesis focuses explicitly on methodological issues within exercise psychology. A critical review of applications of GTM within exercise psychology is conducted. Results reveal that many existing studies.demonstrate a poor understanding of GTM and/or fail to present an adequate account of the research process. Ultimately the results of study 2 provide valuable implications for study 3 of this thesis, which adopts GTM to develop an ecologically valid explanatory model of long-term PA behaviour change. Twenty-one adult participants (9 male, 12 female), aged between 38 and 62 years, were recruited from a countywide PA referral scheme. All participants had made long-term, positive changes to their PA habits. Participants contributed to 25 in-depth interviews. All sampling and analytical procedures were dictated by the key tenets of GTM and a constructivist theoretical stance. To assist with the GTM process, the software package QSR-NVivo was used throughout. A grounded theory of longterm PA behaviour change is presented in the form of a multidimensional explanatory model. The model identifies a number of observed cognitive processes, which appear central to PA behaviour change and maintenance. The underlying mechanisms responsible for these are also highlighted. Results are discussed with specific emphasis on literature surrounding value theories, core beliefs and the introduction of prominent clinical psychology and psychotherapy approaches within exercise psychology. Finally, implications for theory development and applied practice are highlighted and directions for future research suggested.
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