Achieving physical activity recommendations for health as part of mental healthcare for adults with severe mental illness (SMI) could enhance clinical, functional and quality of life outcomes. We have co-designed a protocol to evaluate the impact of an intervention which combines High Intensity Interval Training (HIIT) and Vigorous Intermittent Lifestyle Physical Activity (VILPA) on clinical, functional and quality of life outcomes in people who have SMI.

Pragmatic clinical trial with an intervention and control arms. Participants will be recruited from two mental health services in two different cities in the same geographical area. Participants who meet the inclusion criteria (>18 years, SMI diagnosis, not at medical risk to practise vigorous physical activity, living in the community) will be included. Those from one service will be assigned to the intervention group and those from the other to the control group. The intervention will take place in the mental healthcare centre and will comprise 16 weeks of group-based HIIT, with transition to an individual lifestyle intervention VILPA over the next 12 weeks—for a total intervention period of 28 weeks. Primary outcome (clinical and functional and quality of life) measures and secondary (self-perception and device-measured fitness, physical activity and sedentary behaviour, and experience) measures will be assessed at baseline and at 16-week, 28-week and 40-week follow-ups. Group differences in change scores will be assessed using linear mixed-effects models with time, group and their interaction as fixed effects, accounting for within-subject correlations.

The study was approved by the Human Ethics Committee of the Institute for Research and Innovation in Life and Health Sciences in Central Catalonia (Spain, CEIm code: 24/007). Data will be shared following publication of results with no end date. Results will be disseminated in peer-reviewed journals and at national and international conferences and will inform the development of recovery protocols for people with SMI.

ClinicalTrials.gov NCT06338917.