Effects of Two Web-Based Interventions and Mediating Mechanisms on Stage of Change Regarding Physical Activity in Older Adults

Background Web-based, theory-driven interventions effectively promote older adults' physical activity. Social-cognitive mechanisms of their effect on stage of change need to be further researched. Methods Older adults were randomly allocated to intervention group 1 (10-week online physical activity program), intervention group 2 (same program plus activity tracker), or delayed intervention control group; n = 351 were analyzed (59.6% of originally allocated individuals). Stages of change for recommended endurance and strength training and social-cognitive predictors of physical activity were assessed using questionnaires at baseline and follow-up. Intervention effects and mediation were investigated using mixed-effects ANOVA and ordinal least squares regression. Results Direct effects on stage of change were found for intervention group 1 regarding endurance training (bintervention group 1 = 0.44, 95% confidence interval [0.15, 0.73]), and both groups regarding strength training (bintervention group 1 = 1.02, [0.71, 1.33], bintervention group 2 = 1.24, [0.92, 1.56]). Social-cognitive predictor changes in task self-efficacy, intention, and action planning explained intervention effect on stage of change, but not to the full extent. Conclusions The results indicate significant web-based intervention effects on physical activity stage, partly mediated by changes in task self-efficacy, intention, and action planning.