Importance Insufficient moderate to vigorous physical activity (MVPA) is a risk factor for cardiovascular disease (CVD). Effective interventions are needed to bridge the intention-behavior gap and increase MVPA, especially among women with prior hypertensive pregnancy disorder (HPD).

Objective To test the effectiveness of two 8-week app-based MVPA interventions (motivation and action) that were based on the integrated behavior change (IBC) model and used evidence-based behavior change techniques from behavioral sciences.

Design, Setting, and Participants This randomized clinical trial (RCT) included women with prior HPD. A purpose-built app was tested from October 2021 to March 2022, with follow-up immediately after the intervention (week 9), 3 months later (week 21), and 12 months later (week 61). The study ended in May 2023. Data were analyzed from March 31, 2022, to June 9, 2024.

Intervention All participants received a wearable fitness tracker and a purpose-built physical activity intervention app and were randomized to 1 of 3 groups (control, motivation, or action): The control group received information on CVD, MVPA, and HPD; the motivation group received the same information as well as motivational interviewing–based counseling; and the action group received the same information as well as behavior change techniques that targeted all processes in the IBC model (motivational, volitional, automatic): motivational interviewing–based counseling, action and coping planning, commitment, positive psychology, and mindfulness-based stress reduction.

Main Outcomes and Measures The primary outcome was MVPA (in minutes per week). Treatment effects were estimated using available case ordinary least-squares regression.

Results A total of 619 women participated in this study: 205 in the control group, 209 in the motivation group, and 205 in the action group. Their mean (SD) age was 38.9 (7.3) years; 386 of 577 participants (67%) had a bachelor’s degree or more and 550 of 577 (95%) were living with a child or children. The mean (SD) weekly MVPA for all 3 groups went from a high baseline of 242 (190) minutes to 197 (208) minutes immediately post intervention. No significant postintervention treatment effects on MVPA were observed for the action group (week 9 treatment effect, −17 [95% CI, −58 to 23] min/wk) or the motivation group (week 9 treatment effect, −3 [95% CI, −58 to 51] min/wk), despite the action intervention positively influencing motivational and volitional processes. The app and intervention components were all evaluated positively by participants.

Conclusions and Relevance In this clinical trial of 2 app-based MVPA interventions among 619 women with prior HPD, no treatment effects on MVPA were observed. Possible explanations include (1) the importance of automatic processes in determining MVPA and the absence of treatment effects on these processes and (2) the high baseline activity levels of control group participants, which may have given less room for the treatments to improve upon. These are important considerations for those designing future MVPA interventions and RCTs.

Trial Registration Netherlands Trial Register Identifier: NL9329