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  • Predictors of exercise adherence and weight control : an application of self-determination theory
    Publication . Silva, Marlene Nunes; Teixeira, Pedro Jorge do Amaral de Melo; Matos, Maria Margarida Nunes Gaspar de
    The present Thesis was set within a longitudinal randomized controlled trial, consisting of a 1-year theory-based behavior change intervention and a 2-year follow-up period with no intervention. This trial included 239 overweight or obese women (age: 37.6±7 y; BMI: 31.5±4.1 kg/m2) who were premenopausal and free from identified disease. The main intervention was designed to increase physical activity and internal motivation, following self-determination theory (SDT). While tested before for other health behaviors with promising results, SDT had never been previously applied to weight management in longterm, controlled designs. Thus, the four studies comprising this Thesis were designed to provide a comprehensive analysis of how a theory-based intervention, implemented to affect specific theory-based mediators, would impact exercise adherence and body weight change both in short and long-term, from a SDT perspective. After a complete description of the study protocol, theoretical framework, and main intervention strategies (study 1), study 2 showed that the intervention was successful in affecting theory-driven mediators, physical activity, and weight change at 12 months (intervention’s end), demonstrating that the socio-contextual characteristics advanced by SDT Abstract -2- are amenable to manipulation, and revealing the potential utility of SDT to shape behavioral interventions targeting the promotion of physically active lifestyles and weight-change. Studies 3 and 4 searched for a more in-depth understanding of the dynamics of exercise motivation by exploring and testing mediational models aimed at outlining theory-based mechanisms and their impact on different types of physical activity at intervention’s end (study 3), and on long-term behavioral exercise regulations and physical activity (24-month) and 36-month weight change (study 4). Convergent with previous research, but extending it into the context of a randomized controlled trial, these studies indicated that perceived needsupportive health care climate, psychological needs for autonomy and competence, and intrinsic motivation mediate the effects of the experimental treatment climate on structured exercise behavior. Furthermore, these variables rested within the causal path of long-term weight loss, providing evidence from a link between experimentally-increased autonomous motivation, long-term physical activity adoption, and 3-year weight management. This application of SDT to physical activity and weight management provides experimental evidence that an autonomy-supportive context facilitates the internalization of regulatory processes, particularly through its effect on exercise-related constructs, which in turn promote long-term positive behavioral and clinical outcomes in overweight/obese women.
    2010-09-29Doctoral thesis Open access Show more