The aim of this Randomised Controlled Trial (RCT) is to test the effects of a structured physical activity (PA) program on symptoms in female outpatients aged 18 to 40 years with a diagnosis of Borderline Personality Disorder (BPD). The main questions it aims to answer are:

1. Does a structured PA program reduce clinical symptoms in patients with BPD?
2. How does the effectiveness of a structured PA program compare to a psychoeducational intervention in reducing clinical symptoms and improving physical activity parameters?

Participants will participate in a 12-week structured PA program preceded by three weekly psychoeducation sessions focused on nutrition (intervention group) or will receive a 12-week psychoeducational program on nutrition and PA (control group).

Researchers will compare the intervention group (structured PA program) and the control group (psychoeducational program) to see if the structured PA program leads to greater improvements in clinical symptoms and physical activity parameters. Moreover, the study includes a multidimensional assessment (physical, psychological, and biological) at four time points: at the start of the treatment (T0), at 6 weeks (mid-treatment, when changes from PA become visible and measurable), at the end of the 3-month treatment period (T3), and at a 3-month follow-up after the treatment (T6).

Background and Objectives This randomised controlled trial (RCT) aims to investigate the effects of a structured physical activity (PA) programme on the symptoms of outpatients who meet DSM-5-TR criteria for Borderline Personality Disorder (BPD). The hypothesis is that these symptoms may improve over the course of the PA treatment. The primary objective is to evaluate the efficacy of a structured PA intervention on reducing clinical symptoms and improving PA-related parameters compared to a psychoeducational intervention on healthy lifestyle.

Study Design The PABORD RCT is a controlled study involving female outpatients aged 18 to 40 years with a BPD diagnosis. Participants will be informed about the study's objectives, procedures, and the potential risks and benefits of the proposed treatments. After confirming inclusion/exclusion criteria, obtaining signed informed consent, and reviewing the data processing information, participants will be randomly assigned to two groups. This trial will be conducted in accordance with the Declaration of Helsinki (World Medical Association, 2013).

Treatment Arms

The study involves two treatment arms:

Intervention Group (n=30): Participants will engage in a 12-week structured PA programme, preceded by three weekly psychoeducational sessions focused on nutrition. This includes three 60-minute PA sessions per week supervised by a personal trainer.

Control Group (n=30): Participants will receive a 12-week psychoeducational programme on nutrition and PA. This programme includes 8 sessions divided into modules of 2 or 3 lessons each, covering topics such as the benefits of PA and sports, healthy eating habits, and health risks associated with a sedentary lifestyle. Sessions will be conducted by a dietitian and a clinical psychologist. At the end of the trial, control group participants will be offered the opportunity to participate in the same PA programme as the intervention group at no cost.

Assessment and Follow-Up

The study includes a multidimensional assessment (physical, psychological, and biological) at four time points: T0 (baseline), 6 weeks (mid-treatment), T3 (end of treatment), and T6 (3-month follow-up). These assessments will include:

• Standardised tests for BPD symptoms and general functioning.
• Physical examinations by a sports physician to create a personalised PA plan and assess health status post-intervention.
• Evaluation of premenstrual syndrome (PMS) and obstetric history to determine potential improvements related to PA.
• Use of an accelerometer for 7 days to monitor movement and sleep-wake patterns, and an app using the Experience Sampling Method (ESM) for real-time mood and psychosocial dimension assessments.
• Use of an app for dietary tracking.
• Blood and saliva sample analysis to detect PA-induced changes at the biological level.

The follow-up aims to determine whether the structured PA intervention results in medium-term improvements in BPD symptoms, sustained PA levels, changes in motivation for PA, and alterations in PMS symptoms. This will be assessed through accelerometer data, ESM mood and social interaction reports, and analysis of selected biomarkers in blood and saliva.

Inclusion Criteria:

• Female gender.
• Age between 18 and 40 years.
• Primary diagnosis of Borderline Personality Disorder (BPD) according to the diagnostic criteria of the DSM-5.
• Outpatient treatment.
• Ability to provide written informed consent.
• Good understanding of the Italian language.
• Proficiency in using a smartphone.
• The presence of ongoing pharmacological and/or psychotherapeutic treatments is not considered an exclusion criterion.

Exclusion Criteria:

• Current pregnancy or planning a pregnancy within the next 6 months.
• Acute psychotic symptoms.
• Comorbidities with Eating Disorders, Substance Use Disorder, and Bipolar Disorder.
• Absolute contraindications to physical exercise, such as medical conditions that interfere with the ability to perform exercise or with the physiological response to exercise tests, e.g., the use of beta-adrenergic blocking agents.