Benefits and harms of structured outdoor physical activity for people with somatic or mental diseases: A systematic review and meta-analysis

Objective: To examine the benefits and harms of structured outdoor physical activity (PA) for people living with one or more somatic or mental diseases. Methods: We identified articles from inception until Marts 2023 in MEDLINE, EMBASE, CINAHL and CENTRAL and citation tracking in Web of Science. We included randomized controlled trials (RCTs) and observational studies examining structured outdoor PA reporting physical function, health-related quality of life (HRQOL), pain or mental outcomes. We used random-effect meta-analyses and investigated heterogeneity in subgroups, sensitivity and meta-regression analyses. Observational studies and studies with insufficient data were summarized narratively. Certainty of evidence was assessed with GRADE. Results: From 4098 hits, 20 studies (19 RCTs and 1 cohort) were included (n: 1759 participants). Studies varied in type of disease and intervention. End of intervention results suggested a small effect on HRQOL (k = 10, SMD = 0.45, 95%CI: 0.19 to 0.71) and physical function (k = 14, SMD = 0.39, 95%CI: 0.13 to 0.64), while effects were moderate on mental outcomes (k = 13, SMD = -0.52, 95%CI: -0.82 to -0.23) favoring the outdoor intervention over comparators (no intervention, usual care, indoor PA or outdoor intervention without exercise). We were not able to conclude on outdoor interventions' effect on pain. Four studies reported adverse events including nonserious (pain, falls, fatigue) and serious (hospitalization, pneumonia). Certainty of evidence was overall very low. Conclusion: Structured outdoor PA may improve HRQOL and physical function, as well as mental health outcomes. The very low certainty of evidence calls for high quality RCTs to determine benefits and harms of structured outdoor PA.