The Mediating Role of Internal Motivation on the Longitudinal Influence of Body Satisfaction on Physical Exercise. Open Access
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Regular exercise is critical for both physical and psychological health. Unfortunately, Americans rarely meet guidelines for adequate exercise, which puts them at risk for various medical problems including heart disease, diabetes, and obesity (Physical Activity Guidelines Advisory Committee, 2008). The current study examined the influence of body satisfaction on exercise through the framework of Self-Determination Theory (SDT; Deci & Ryan, 1985. I hypothesized that body satisfaction would relate to more exercise prospectively; that internal motivation and exercise enjoyment would mediate the association between body satisfaction and exercise; and that body satisfaction would predict a change in exercise over time. I also hypothesized that stage of change (an individual's readiness to act on a new behavior; Marcus & Owen, 1992) would moderate the association between body satisfaction and exercise such that the relation between body image and exercise would be stronger than for maintainers compared to initiators. To test these hypotheses, participants (N = 112) completed online questionnaires at Time 1 and one month later at Time 2 indicating their body satisfaction, internal motivation, exercise enjoyment, typical exercise frequency, habit strength, and duration of mild, moderate, and vigorous activity. Participants also completed daily diaries each night and wore Fitbits to get real time, objective measures of exercise. Results supported the first hypothesis for habit strength, exercise frequency, and marginally for daily diaries. Body image did not predict exercise measured by the Fitbits or the IPAQ. Both measures of internal motivation - exercise enjoyment and the second version of the Behavioral Regulations in Exercise Questionnaire (BREQ-2) mediated the association between body satisfaction and exercise for all measures of exercise except the Fitbits and the International Physical Activity Questionnaire (IPAQ), partially supporting the second hypothesis. The third hypothesis was also partially supported. Body image predicted a change in exercise frequency and habit strength, but this association was strongest for maintainers rather than initiators. This suggests that body satisfaction may be a crucial factor in motivating healthy, weight control behaviors such as exercise.