Using the transtheoretical model to predict physical activity level of overweight adults with serious mental illness

Although physical activity (PA) is recommended for individuals with serious mental illness (ISMI), most of them are inactive or insufficiently active. The transtheoretical model (TTM) has been proposed to explain the motivational factors associated with PA however, there is little evidence of its applicability to ISMI. So, the objective was to analyse whether TTM components are related to PA in overweight ISMI. In this cross-sectional study, participants completed the Global Physical Activity Questionnaire to assess their PA level and TTM components: stages of change (SOC), decisional balance (pros and cons), self-efficacy and processes of change (POC; experiential and behavioural). 43 overweight ISMI (27 males, mean age 29.0 ± 6.64, mean BMI 31.91 ± 5.10kg/m², 30% with schizophrenia, and 44% inactive), referred to a PA programme were recruited. PA was positively correlated with POC and perceived pros, with TTM constructs accounting for 14.5% of PA variance. Mean level of behavioural POC and perceived pros were higher in physically active than in inactive participants. So, this study confirms that TTM components are associated with PA in overweight ISMI. Therefore, the TTM should be considered when planning PA interventions for ISMI.