A three-arm pilot rater-blinded randomized controlled trial is conducted, comprising Yoga-based Group Intervention (YoGI + TAU) as the experimental condition, a strength and flexibility training (SFT + TAU) group, and treatment as usual (TAU). Participants in all conditions receive the respective intervention in addition to treatment as usual (TAU) in outpatient settings in Germany. The interventions are designed for patients with schizophrenia spectrum disorders. To examine feasibility, acceptability, and preliminary efficacy, self-report measures and blinded rater-based assessments are administered at baseline (T0), after 12 weeks of participation (T1), and at a 3-month follow-up (T2). Before each intervention session, acute stress (general stress and symptom-related distress) is measured using a visual analogue scale. After each intervention session, acute stress (general stress and symptom-related distress; visual analogue scale), perceived effort (BORG-RPE-Scale), and the occurrence of unpleasant experiences are recorded via self-report, while instructors rate exercise performance and overall participation quality. In addition, semi-structured interviews are conducted at T0 and T1 to assess subjective mechanisms of change and relevant processes.

The primary outcomes of this trial are the feasibility and acceptability of YoGI and the SFT, assessed through recruitment and retention rates, adherence, and participant feedback. Based on recommendations for pilot studies of 20-50 participants, a conservative target sample size of 60 patients was determined. Further, the trial will evaluate secondary outcomes, including (body) mindfulness (SMQ, BMQ), symptoms of depression, anxiety, and stress (DASS, CDSS), positive and negative symptomatology (PANSS), psychological flexibility (CFQ), psychological well-being (WHO-QoL-BREF), social functioning (PSP), subjectively perceived cognitive functioning (SSTICS), and physical activity (SIMPAQ). This study aims to provide preliminary evidence for the efficacy of YoGI in comparison to both SFT and a TAU, and to establish a foundation for a future fully powered randomized controlled trial.

Patients are recruited across Berlin through psychiatric outpatient departments, the outpatient clinics of Charité, and social media. Recruitment occurs either through direct approach by psychologists or psychotherapists in training, or via informational posters and flyers. At baseline, eligibility screening is conducted by a blinded psychologist who is independent of the intervention delivery. This psychologist introduces the study, obtains electronic informed consent, and administers the self-report and clinician-rated assessments.

Given the behavioral nature of the interventions, participants and therapists are informed about group allocation after randomization. Randomization is performed using an Excel-generated list with block randomization (block size = 4).

Data management adheres to standard data protection procedures, including the use of anonymized identification codes and secure storage in an online database accessible only to authorized research team members. Participants retain the right to access their data and to request its deletion at any time. Upon completion of the study, each participant will receive compensation of 50 €.

Inclusion Criteria:

• Diagnosis of Schizophrenia Spectrum Disorder by previous (medical) reports according to ICD-10/ DSM-V
• Treated as psychiatric outpatients
• Age between 18 and 65 years
• Ability to give informed consent
• Willingness and ability to engage in psychotherapeutic group therapy
• Low to moderate psychotic state indicated with a score of ≤ 6 for each item at the Positive scale of the Positive and Negative Syndrome Scale (PANSS, Peralta & Cuesta, 1994)

Exclusion Criteria:

• Neurological disorders and history of severe traumatic brain injury in the past that may affect cognitive functioning
• Acute substance dependence, excluding nicotine and prescribed medication
• PANSS-P score on one item > 6 (= very severe)
• Ineligibility for group participation
• Acute suicidality, indicated by a score > 1 on item 8 of the Calgary Depression Scale for Schizophrenia (Addington, Addington, Maticka-Tyndale, & Joyce, 1992)
• Conflicting co-therapy such as electroconvulsive therapy or ketamine treatment as well as intensive psychotherapy

Outcome assessments are conducted by a blinded psychologist or psychiatrist who is independent of the study therapists. Due to the psychotherapeutic nature of the interventions, treatment allocation cannot be concealed from participants or care providers. Randomization is performed using a block randomization procedure with a block size of four, generated in Microsoft Excel to ensure balanced group allocation.