The intervention was a significant positive predictor of intermediate-term change in specific self-efficacy towards physical activity barriers (β = .183; SE = .089; p = .044) and of coping with relapse (β = .436; SE = .215; p = .046), and a marginally significant positive predictor of intermediate-term change in social support from family (β = .339; SE = .196; p = .088). For the different types of motivation, modeling, social norm, social support from friends and partner, general self-efficacy, benefits and barriers, no significant results were found (all p > .10). Therefore, only change in self-efficacy towards physical activity barriers, change in social support from family and coping with relapse were analyzed as potential mediators of the intermediate-term (pre-follow up) intervention effects on changes in physical activity behaviors.