Testing the Efficacy of a Theory-Based Online Physical Activity Promotion Intervention for Inactive Parent-Child Dyads: A Randomized Controlled Trial

Background:Physical inactivity is a major public health concern, associated with increased chronic disease risk and diminished quality of life. Despite clear guidelines, most children and adults do not meet recommended physical activity levels. The transition from childhood to adolescence is marked by a notable decline in regular moderate-to-vigorous physical activity, often persisting into adulthood, while parents are also less active than other adults. Family-based interventions, particularly those engaging parent-child dyads, have shown promise for promoting physical activity, but many have a limited basis in behavioral theory that provides detail on the mechanisms of behavior change.Objective:This study aimed to evaluate the efficacy of a theory-based, family intervention, known as Proact, designed to increase physical activity among low-active Finnish parent-child dyads, and targeted behavior change in motivational and belief-based behavioral determinants from self-determination theory, the theory of planned behavior, and dual process models.Methods:The study adopted a randomized controlled design with low-active parent-child dyads recruited from the Finnish population. Neither the parent nor child in each dyad met physical activity guideline recommendations and children were aged 8 to 12 years. Dyads were randomized to Proact intervention or waitlist control groups. The intervention comprised four web-based sessions supported by online resources and SMS prompts. Materials included instruction and training on autonomy-supportive parenting, as well as materials targeting goal setting, planning, and social support for both parents and children. Primary (self-reported physical activity) and secondary outcomes (autonomous motivation, attitude, subjective norm, perceived behavioral control, intention, self-monitoring, self-reported habit) were assessed at baseline, 3 months (post-intervention), and 6 months. Data were analyzed using linear mixed models.Results:Of the 140 dyads enrolled, 88 parents and 75 children provided baseline data, but attrition was high at follow-up points. Although self-reported physical activity trended upwards post-intervention, no statistically significant intervention effect on self-reported physical activity was observed. Significant increases in perceived behavioral control, attitude, and self-monitoring were observed at 3- and 6-month post-intervention follow-up in the intervention group. Limitations included high attrition and low session attendance and the sample primarily comprising highly motivated Finnish mothers and their children.Conclusions:Although the intervention led to positive changes in some of the theory-based psychological determinants of physical activity implicated in the mechanism for behavior change, it did not lead to significantly increased activity levels in inactive parent-child dyads. Findings were likely affected by high dropout rates and limited intervention engagement.