Abstract
A substantial body of research has linked the built environment to obesity risk in older adults, with physical activity reducing obesity risk. Most studies have focused on temperate and subtropical regions; however, results can vary due to different climate characteristics. This study examines Lanzhou, a representative of arid Northwestern China, to explore the nonlinear relationship between the built environment and physical activity among older adults, focusing on the role of green spaces. By using the XGBoost method, we analyze how green spaces and the 5D built environment affect physical activity levels among the obese and standard-weight elderly populations in Lanzhou. Results indicate that green spaces significantly influence physical activity in both groups, with their effect surpassing other environmental and sociodemographic factors. Obese elderly individuals are more influenced by green space quality and accessibility, while standard-weight individuals are more affected by the overall quantity and coverage of green spaces. Obese individuals also rely more on street greening compared with their standard-weight counterparts. In addition, a diverse urban environment and appropriate public transportation distances are crucial for promoting physical activity among the elderly. Low temperatures inhibit physical activity more in obese elderly individuals. Our findings provide insights for policymakers, planners, and designers on optimizing green infrastructure to reduce obesity risks among the elderly in arid regions, ultimately enhancing the urban environment's effectiveness in promoting healthy aging.