Abstract
BACKGROUND: Physical inactivity is associated with health risks, contributing to various diseases and all-cause mortality. Despite recommendations for regular physical activity (PA), many adults remain inactive, influenced by socioeconomic and environmental factors. Digital interventions, particularly web-based PA programs, offer promising possibilities to promote PA across populations. These programs vary in their effectiveness, reflecting differences in design, user engagement, and behavior change techniques employed. OBJECTIVE: This study evaluates the effectiveness of the 12-week multimodal web-based TKFitnessCoach. The PA online program is part of the TK-HealthCoach. This study investigates the program's impact on self-reported PA levels, goal attainment, healthrelated quality of life, body weight, and eating behavior, comparing an interactive personalized web-based intervention and non-interactive web-based health information. METHODS: In a randomized controlled trial (RCT), participants were allocated to either the intervention group (IG), receiving access to the interactive TK-FitnessCoach, or the control group (CG) that was provided a static website with evidence-based information on PA. The study targeted a German-speaking adult population interested in improving health behavior. Data was assessed at T0 (beginning of the study), T1 (postintervention), T2, 6 months, and T3, 12 months follow-ups, focusing on self-reported PA at T3 and on various secondary outcomes. RESULTS: We achieved equally distributed sociodemographics in both the IG and the CG with a mean age of 42.8 (IG), resp. 43.1 years (CG), and female participants of 76.1 % (IG), resp. 74.7 % (CG). PA at baseline was 277.9 min/week in the IG and 273.3 min/week in the CG. Both, the IG (n = 1153 in the Intention-to-treat (ITT) dataset) and CG (n = 1177 in the ITT dataset) exhibited significant increases in PA over time (IG(T3-T0) = 72.92 min/week; CG(T3-T0) = 74.12 min/week).However, the study did not find significant differences in the effectiveness of the interactive TK-FitnessCoach compared to the non-interactive control in terms of improving PA and related health outcomes. The intensity of using the TK-FitnessCoach was not associated with PA. CONCLUSIONS: Both programs were effective in promoting PA among adults, with no significant differences observed between the two RCT groups. This highlights the potential of digital interventions in addressing physical inactivity, suggesting that the effectiveness of such programs may not solely depend on their interactivity but also on the quality and relevance of the information provided. Further research is needed to explore optimization strategies for such interventions, especially for persons with low PA, including user engagement, behavior change techniques, and the integration of objective PA tracking methods. TRIAL REGISTRATION: German Clinical Trials Register DRKS00020249; https://drks.de/search/en/trial/DRKS00020249.