Abstract
BACKGROUND: The benefits of physical activity are well-documented, and healthy habits established in childhood often continue into adulthood. Recent research has shown that schoolyards provide a valuable platform for children to be physically active, with greener spaces in particular enhancing both physical and mental well-being. The City of Stockholm has formally decided to reconstruct 20 schoolyards, incorporating more play areas and greenery. This study will evaluate the impact of these reconstructions, aiming to increase physical activity levels among schoolchildren across all socioeconomic groups, while also contributing to climate change mitigation in urban environments. METHODS: This study will utilize a stepped-wedge design, where each school undergoing schoolyard reconstruction will serve as both a control and intervention site. Over four years, from 2024 to 2027, five schools will have their schoolyards reconstructed each summer. Control data will be collected in the spring prior to the reconstruction, with follow-up data collected in the spring after the reconstruction. We aim to recruit 3 600 children aged 6 to 12 years. The primary outcome will be changes in physical activity, measured via accelerometers. Secondary outcomes will include changes in musculoskeletal fitness, perceptions of the schoolyard, and environmental impact. Given the 24-hour constraint of daily time, movement behaviors (e.g., MVPA, LPA, SB, and sleep) will be treated as compositional data. Log-ratio transformation will be applied and introduced as outcomes in general linear mixed models, with schools treated as random effects. DISCUSSION: This large-scale study has the potential to set new guidelines for physical health policies in schools across the City of Stockholm, potentially influencing the well-being of an even greater number of children. Additionally, the study could provide valuable insights into strategies for mitigating climate change through urban design, offering a model for sustainable school environments that promote both health and environmental resilience. TRIAL REGISTRATION: The trial has been registered on ClinicalTrials.gov the 19th of May 2023, with the reference number NCT05865782. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-026-26609-9.