Non-linear effects of the urban green space on promoting restorative physical activity among older adults living with different chronic disease status in semi-arid area: a case study of Lanzhou, China

Introduction In the context of an aging society, promoting restorative physical activity for older adults with chronic diseases is of significant importance. This study focuses on the main urban area of Lanzhou, China, as a case study to explore the non-linear relationship between urban green space and the restorative physical activity level of older adults. Methods Utilizing community health physical examination data from 2021, we selected a sample of 1,773 older adults from 14 communities and categorized them into three levels of restorative physical activity. The research employs a Genetic Algorithm to optimize the CatBoost model. By controlling for individual characteristics and comprehensively incorporating built environment and green space indicators, the GA-CatBoost model was utilized to analyze the non-linear impacts and threshold effects. Results The results indicate that the influence of green space varies significantly among older adults with different health statuses. The restorative physical activity levels of healthy older adults are primarily affected by built environment factors, whereas older adults with chronic diseases are more influenced by green space. For instance, when the distance to a park exceeds the threshold of 400 meters, the restorative physical activity levels of older adults with chronic diseases experience a dramatic decline. It was observed that when the park distance is within 220 meters, the restorative physical activity levels of healthy older adults show a positive correlation with distance; however, beyond this threshold, the correlation becomes negative. Conclusion The study reveals that excessive greening intensity may inhibit activity among older adults, while a moderate and continuous green environment is more conducive to promoting activity among older adults with chronic diseases. Our findings provide valuable insights for policymakers and planners into optimizing green spaces to mitigate chronic disease risks among older adults in arid regions. This research serves as an empirical reference for enhancing urban environmental quality to promote healthy aging.