OUTSIDE 2: Outdoor swimming as a nature-based intervention, offered in addition to usual care, compared to usual care alone, in people with depression: A study protocol for a randomised controlled trial and economic evaluation

OUTSIDE 2: Outdoor swimming as a nature-based intervention, offered in addition to usual care, compared to usual care alone, in people with depression: A study protocol for a randomised controlled trial and economic evaluation | medRxiv Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search OUTSIDE 2: Outdoor swimming as a nature-based intervention, offered in addition to usual care, compared to usual care alone, in people with depression: A study protocol for a randomised controlled trial and economic evaluation View ORCID Profile Heather Massey , View ORCID Profile Hannah Denton , View ORCID Profile Anna-Marie Bibby-Jones , View ORCID Profile Stephen Bremner , View ORCID Profile Mara Violato , View ORCID Profile Amy Burlingham , View ORCID Profile Rebecca Cunningham , Sabrina Hasnaoui , View ORCID Profile Mark Harper , View ORCID Profile Sam Robertson , Sandy Ciccognani , View ORCID Profile Kay Aranda , View ORCID Profile Amy Arbon , Gail Murphy , View ORCID Profile Chloe Bruce , Debbie Lambert , View ORCID Profile Clara Strauss doi: https://doi.org/10.64898/2026.03.17.26348590 Heather Massey 1 Extreme Environments Laboratory, School of Psychology, Sport and Health Sciences, University of Portsmouth 2 Sussex Partnership NHS Foundation Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Heather Massey For correspondence: Heather.massey{at}port.ac.uk Hannah Denton 2 Sussex Partnership NHS Foundation Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Hannah Denton Anna-Marie Bibby-Jones 2 Sussex Partnership NHS Foundation Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Anna-Marie Bibby-Jones Stephen Bremner 3 Florence Nightingale Faculty of Nursing, Midwifery & Palliative Care, Division of Methodologies Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Stephen Bremner Mara Violato 4 Health Economics Research Centre, Nuffield Department of Population Health, University of Oxford Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Mara Violato Amy Burlingham 5 Herefordshire and Worcestershire Health and Care NHS Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Amy Burlingham Rebecca Cunningham 6 Birmingham and Solihull Mental Health Foundation Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Rebecca Cunningham Sabrina Hasnaoui 7 Coventry and Warwickshire Partnership NHS Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site Mark Harper 8 Royal Sussex County Hospital , Brighton, UK 9 Sørlandet Sykehus , Kristiansand, Norway Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Mark Harper Sam Robertson 2 Sussex Partnership NHS Foundation Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Sam Robertson Sandy Ciccognani 2 Sussex Partnership NHS Foundation Trust Find this author on Google Scholar Find this author on PubMed Search for this author on this site Kay Aranda 10 School of Education, Sport and Health Sciences, University of Brighton , BN1 9PH Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Kay Aranda Amy Arbon 11 Brighton & Sussex Clinical Trials Unit, Brighton and Sussex Medical School , Brighton Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Amy Arbon Gail Murphy 11 Brighton & Sussex Clinical Trials Unit, Brighton and Sussex Medical School , Brighton Find this author on Google Scholar Find this author on PubMed Search for this author on this site Chloe Bruce 11 Brighton & Sussex Clinical Trials Unit, Brighton and Sussex Medical School , Brighton Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Chloe Bruce Debbie Lambert 11 Brighton & Sussex Clinical Trials Unit, Brighton and Sussex Medical School , Brighton Find this author on Google Scholar Find this author on PubMed Search for this author on this site Clara Strauss 2 Sussex Partnership NHS Foundation Trust 12 School of Psychology, University of Sussex Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Clara Strauss Abstract Full Text Info/History Metrics Supplementary material Data/Code Preview PDF Abstract Background Major depression affects at least 10% of adults, yet evidence-based treatments have modest clinical effectiveness and acceptability. In recent years, outdoor swimming has grown increasingly popular and emerging quantitative and qualitative evidence suggests potential as an intervention for depression, however, there is yet to be a full-scale randomised controlled trial (RCT). This is a protocol to assess the safety and test the clinical- and cost-effectiveness of an 8-session outdoor swimming course (in addition to usual care) on depression symptom severity in adults experiencing major depression, in comparison to usual care alone. Methods This study is a pragmatic, parallel group, superiority RCT with 1:1 allocation comparing the outdoor swimming intervention (in addition to treatment as usual) with treatment as usual, aiming to recruit 480 adult participants meeting diagnostic criteria for major depression. Recruitment will take place across 21 sites with blind post treatment and follow up assessments. The primary outcome is depression symptom severity at T1 post-intervention, 12 weeks post-randomisation (the primary end point) using the Patient Health Questionnaire 9 (PHQ-9). Secondary clinical outcomes are anxiety (Generalised Anxiety Disorder 7 at T1 and T2 [38 weeks post-randomisation] and PHQ-9 at T2), mindfulness is measured as a potential mechanism at all timepoints (Five Facet Mindfulness Questionnaire 15). Health economic measures at all time points are: EQ-5D-5L, Recovering Quality of Life (ReQoL), Client Service Receipt Inventory and the Productivity Cost Questionnaire. A qualitative study will examine the experience of participants during and after the swim course. Discussion If the 8-session outdoor swim course is safe, clinically- and cost-effective, findings will support national implementation, offering an evidence-based intervention to those affected by depression, while potentially reducing healthcare costs. Furthermore, this may pave the way for other outdoor activities to support people with poor mental health to be developed and evaluated as interventions. Trial registration Controlled trial registration number is ISRCTN registration number 24759023. Registered on 21 February 2024 ( https://www.isrctn.com/ISRCTN24759023 ). Administrative information Note: Numbers enclosed in braces within this protocol correspond to SPIRIT checklist item numbers. The sequence of items has been adjusted to group related content together. ( https://www.consort-spirit.org/ ). View this table: View inline View popup Download powerpoint Background Depression is very common,with at least 1 in 10 people having an episode of depression during their lifetime. Many people believe that outdoor swimming can improve depression. There is some research that suggests outdoor swimming is helpful for depression, but we do not yet have enough evidence to be sure. OUTSIDE 2 is a large research study that aims to find out whether outdoor swimming can help people with depression. Aim The aim of this study is to find out if taking part in an 8-session outdoor swimming course, along with usual care, is safe, helps improve depression, and is good value for money. We will compare people who do the swimming course (alongside their usual care) with people who only receive their usual care. In our study we will also talk to participants about their experiences. We want to understand how the outdoor swimming course affects their depression, and how the activity itself might help them feel better. Describe your research plan, including People who are interested in taking part in the study can visit our website (outside2.co.uk) to read more information and sign up. Once someone agrees to join, they will be randomly placed into one of two groups available at their location to keep the study fair. One group will take part in eight one-hour outdoor swimming sessions in a small group. They will continue with their usual care for depression, which may include talking therapies, antidepressant medication, or community activities. The other group will continue with usual care only during the study. After the study ends, they will be offered the same outdoor swimming course, so no one misses out. The swimming sessions will be led by experienced swimming coaches who will help participants build confidence in the water and learn important water safety skills. During the study, all participants will complete questionnaires about their symptoms of depression, overall mental health, and use of health services. They will do these before they are put in a group, right after the swimming course or usual care period and six months later. Participants in the swimming group will also be asked to keep a diary about their experiences during the course. Researchers may visit some sessions to ask participants about how they are finding the swimming and how it affects their mood. Swim coaches will record attendance at each session and describe what activities were included. This helps the research team understand exactly what took place during each class. Knowledge mobilisation We want to make sure that the information we learn from this study reaches many different people, not just scientists. To do this, we will share our findings in several ways. We will create a Podcast mini-series, an animated video as well as research papers. Using these different methods helps us share our findings with many groups, including adults in the community, mental health professionals, people working in the swimming industry, scientists, and policymakers. By sharing the results in several ways, more people can understand if and how outdoor swimming might support recovery from depression and mental health more broadly, and it increases the chance that the study will make a real difference, whatever it finds. Competing Interest Statement There are potential conflicts of interest as some of the authors of the research team are trustees (HM) or advisors (HD, AB & MH) to Community Interests Companies that support outdoor swimming, MH is also the author of a book about outdoor swimming. Therefore, the research team agrees to publish the results of this study, irrespective of the findings. Clinical Trial ISRCTN24759023 Funding Statement This project is funded by the National Institute for Health and Care Research (NIHR) [Policy Research Programme (ST-01-51), (ref. number NIHR203462)]. CS is partly supported by National Institute of Health Research funding awarded to the Applied Research Collaboration in Kent, Surrey and Sussex. MV was partly supported by the NIHR Oxford Health Biomedical Research Centre (award number NIHR2033160 and received funding from the NIHR Applied Research Collaboration Oxford and Thames Valley (award number NIHR200172). The funding bodies have not influenced the design, conduct, analysis or dissemination of this study. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, NIHR or the Department of Health and Social Care. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: National Health Service Research Ethics Committee (London - Hampstead) gave ethical approval for this work (23/LO/0942). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes hannah.denton3{at}nhs.net anna-marie.bibby-jones{at}nhs.net stephen.bremner{at}kcl.ac.uk mara.violato{at}dph.ox.ac.uk amy.burlingham{at}nhs.net rebecca.cunningham1{at}nhs.net sabrina.hasnaoui{at}nhs.net mark.harper{at}doctors.org.uk sam.robertson6{at}nhs.net SandyCiccognani{at}gmail.com K.Aranda2{at}brighton.ac.uk a.arbon{at}bsms.ac.uk g.murphy{at}bsms.ac.uk c.bruce{at}bsms.ac.uk D.Lambert{at}bsms.ac.uk clara.strauss{at}nhs.net Data Availability No underlying data or extended are associated with this article. The SPIRIT (2025) checklist for OUTSIDE 2: Outdoor swimming as a nature-based intervention for depression is available at https://doi.org/10.25377/sussex.3144518868 https://doi.org/10.25377/sussex.3144518868 Abbreviations AE Adverse Event BSCTU Brighton and Sussex Clinical Trials Unit CI Chief Investigator CSRI Client Service Receipt Inventory DMEC Data Monitoring and Ethics Committee EQ-5D-5L Euroqol 5-Dimension 5-Level instrument FFMQ-15 Five-Facet Mindfulness Questionnaire GAD-7 General Anxiety Disorder-7 GCP Good Clinical Practice GP General Practitioner HRQoL Health-related quality of life ISRCTN International Standard Randomised Controlled Trial Number LEAP Lived Experience Advisory Group MINI Mini International Neuropsychiatric Interview NICE National Institute for Health and Care Excellence PHQ-9 Patient Health Questionnaire-9 PIC Participant Identification Centre PIS Participant Information Sheet PPI Patient and Public Involvement RCT Randomised Control Trial REC Research Ethics Committee ReQoL-10 Recovering Quality of life - 10 items SAE Serious Adverse Event SMG Study Management Group SOP Standard Operating Procedure SPFT Sussex Partnership Foundation Trust TSC Trial Steering Committee Copyright The copyright holder for this preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license . Back to top Previous Next Posted March 19, 2026. Download PDF Supplementary Material Data/Code Email Thank you for your interest in spreading the word about medRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. You are going to email the following OUTSIDE 2: Outdoor swimming as a nature-based intervention, offered in addition to usual care, compared to usual care alone, in people with depression: A study protocol for a randomised controlled trial and economic evaluation Message Subject (Your Name) has forwarded a page to you from medRxiv Message Body (Your Name) thought you would like to see this page from the medRxiv website. Your Personal Message CAPTCHA This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. 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