Physical activity in the management of personality disorders: protocol for a three-arm randomized feasibility trial

Background Borderline personality disorder (BPD) and avoidant personality disorder (AVPD) are both characterized by emotional dysregulation, low and unstable self-esteem, interpersonal difficulties, and associated with impaired physical health. Physical activity (PA) may benefit both mental and physical well-being, yet evidence on structured, tailored interventions for these populations is limited. This trial investigates the feasibility, acceptability, and safety of two PA interventions—pedometer-based walking combined with treatment as usual (TAU), and karate training combined with TAU—compared with TAU alone in adults with BPD or AVPD. Methods This trial is a three-arm, randomized feasibility trial aiming to recruit 60 adults with BPD or AVPD who are receiving TAU at the time of recruitment from two specialized psychotherapeutic outpatient clinics in the Capital Region of Denmark. Participants will be allocated (1:1:1) to TAU, karate combined with TAU, or pedometer-based walking combined with TAU. TAU will include standard individual and/or group psychotherapeutic treatment. The karate intervention will consist of twice-weekly group sessions over 8 weeks led by experienced karate instructors with knowledge of personality disorders. The walking intervention will involve individually tailored goals, pedometers, diaries, and regular motivational check-ins with the research staff. Primary outcomes will include feasibility measures, such as recruitment, retention, adherence, and safety. Secondary outcomes will include objective measures (body composition, cardiorespiratory fitness) and self-reported measures of emotion regulation, personality disorder symptoms, interpersonal functioning, personal recovery, PA behavior, body awareness, and body image. Qualitative interviews will explore participants’ experiences, perceived value, and barriers to engagement. Adverse events will be monitored throughout the trial. Discussion This trial will address a critical gap in research on PA interventions for BPD and AVPD by testing structured, tailored PA programs. Findings will inform the design of a future full-scale randomized controlled trial, including recruitment strategies, intervention delivery, and safety procedures, and will provide insights into the acceptability and potential benefits of PA in these populations. Trial registration This trial was prospectively registered on clinicaltrials.gov (NCT07341438) on 14 January 2026.