Abstract
While physical activity (PA) is recommended to persons with overweight, many of them do not or do not have the willingness to practice it (Kearney et al., 1999). Through the theories of motivation, the transtheoretical model developed by Prochaska and DiClemente (1983) is an integrative approach which allow to take into account for the change in behavior, particularly with regard to PA (Farmanbar et al., 2012). Based on this approach, the present thesis aimed to understand the mechanisms related to the adoption and cessation of PA. A first study whose purpose was to validate a questionnaire of processes of behavior change revealed a five-factor factorial structure, invariant among sex, and predictive of the PA behavior. A second study showed that, after a one-week intervention designed to improve the management of the overweight, some processes identified by the questionnaire were involved in behavior change regarding PA. Thus, one year after the intervention, three processes were activated among participants that having adopted or maintained their PA: processes of helping relationship, consciousness raising and self-reevaluation/ reinforcement management / self-liberation. A third study sought to examine the relationships between some motivational (self-efficacy, basic psychological need, motivational regulations), affective (perceived pleasure), of eating behavior (cognitive restraint) and physiological (glucodependence, maximal lipid oxidation) variables and the cessation of a program of PA. Then, a fourth study aimed to examine the dynamic of these same motivational, affective and behavioral variables during a training program of seven weeks which aim to active some processes of change. Increases in self-efficacy expectations, identified and intrinsic regulations, perceived pleasure were observed.