To promote both physical and mental health, reduce the risk of lifestyle-related diseases and prevent premature death, the World Health Organization recommends that adults aged 18-64 should participate in at least 150 minutes of moderate-intensity or 75-minute vigorous- intensity physical activity per week. In Sweden, more than one third of the population is physically inactive and there is a need for more effective methods to increase physical activity at the community level. The purpose of this study was to examine how the participants in the different stages of change differed in terms of the constructs in the Transtheoretical model (TTM), and whether a stage-matched intervention could contribute to increased psychological readiness and/or physical activity among participants in the Contemplation or Preparation stage. A survey followed by an intervention was conducted. The intervention was divided into two experimental groups and two control groups. For analysis purposes the two experimental groups (n = 32) and the two control groups (n = 49) were combined. The results showed that the stages of change were not completely separated from each other with respect to the constructs in TTM, and that the participants in the combined experimental group reported higher self-efficacy and fewer perceived Disadvantages after the intervention. In addition, an interaction effect for self-efficacy was demonstrated. Despite the study's limitations, the results show that stage-matched intervention has potential to increase self-efficacy and thus psychological readiness among the individuals who are in the Contemplation or Preparation stage.

Keywords: Transtheoretical Model, physical activity, behavior change, e-mail.