Fessler, L., Maltagliati, S., Meyer, P., Finckh, A., Cullati, S., Sander, D., Friese, M., Wiers, R., Farajzadeh, A., Luthy, C., Sarrazin, P., & Cheval, B. (2026). Anatomy of a Failure: A Retrospective Evaluation of a Cognitive Bias Modification Intervention to Promote Physical Activity in Cardiac Rehabilitation. BMJ Open. This article was accepted on 29 January 2026. Therefore, the online version is not yet available. The associated preprint can be found at: https://doi.org/10.1101/2025.02.27.25323019.

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Objectives. Promoting regular physical activity (PA) is essential in cardiac rehabilitation; yet many patients exhibit low levels of PA. In January 2022, the Improving Physical Activity (IMPACT) trial, a randomised controlled trial at the University Hospital of Geneva, was launched to promote PA in cardiac patients by targeting automatic approach tendencies towards exercise-related stimuli through a cognitive bias modification (CBM) intervention. This article examines the limited acceptance of this intervention, identifies potential barriers, and proposes strategies to improve future implementations.

Design. Retrospective evaluation of a pre-registered clinical trial.

Setting. The intervention was conducted in a cardiac rehabilitation centre in Switzerland. Participants. Sixty-eight cardiac rehabilitation patients (Mage = 57.76, SD =10.76 years, 87% male).

Intervention. Patients received 12 CBM sessions over 6 weeks, designed to target approach-avoidance tendencies to exercise-related stimuli and improve PA levels.

Primary and secondary outcome measures. Acceptance was assessed using behavioural (e.g., enrolment and engagement rates), cognitive (e.g., perceived effectiveness), and emotional (e.g., affective evaluation) indicators. The cognitive and emotional indicators were derived from verbal feedback documented by the research assistants based on patients′ reactions during the intervention period. These observations do not constitute qualitative research as defined by methodological standards; they were informal notes provided by RAs during intervention delivery and were not collected or analysed using qualitative research methods.

Results. Of the 352 patients initially required, only 68 (19%) were enrolled. Among these 68, 63% completed the minimum number of CBM sessions, and 25% completed accelerometer-based PA measures during the week following discharge. These behavioural indicators of low acceptance showed cognitive (e.g., scepticism about the task relevance and perceived effectiveness of the intervention) and emotional (e.g., feelings of boredom and disinterest) barriers.

Conclusion. The low engagement and acceptance observed in the IMPACT trial reveal highlight several key barriers, such as perceived task irrelevance, task monotony, and task boredom, that undermine the acceptance and feasibility of this digital CBM intervention in cardiac rehabilitation. These findings emphasise the importance of designing patient-centred interventions, ensuring their seamless integration into clinical contexts, and conducting qualitative research prior to implementation to anticipate potential barriers.