This research stems from the worldwide public health problem of childhood obesity and insufficient physical activity (PA) among adolescents. Studies have shown that both social networks and the built environment could affect PA, but how do they jointly exert influence? Understanding the scale and mechanism of this joint impact could shed light on developing an effective intervention to promote PA. The goal of this dissertation is to try to disentangle the joint influence of social networks and the built environment on changes in PA through social network analysis and test a novel intervention based on the findings from the social network models. This study uses two waves of Add Health data from two sample schools. Chapter Two investigates how school-based friendship networks could influence Physical Education (PE) class enrollment. Chapter Three examines the influence of home location, neighborhood characteristics, as well as the demographic characteristics and change in PA of peers who were nominated as friends in the Add Health social survey on high school student’s friend selection and PA dynamics between two academic years. Chapter Four presents a spatial agent-based model that was derived from the social network model and integrates a location-based mobile game similar to Pokémon Go as a PA-promoting intervention to test different intervention scenarios. Through this research, I demonstrate that friends’ PE enrollment status has a weak influence on the change of individual’s PE enrollment in two consecutive years. Another observation is that student’s total PA change can affect their PA behaviors. Contrarily, the built environment of the neighborhood did not prove to exert significant influence. Due to social influence, students participating in an intervention program may cause a change in PA of non-participants, i.e., we can observe a spillover effect of the intervention program. This dissertation enriches the field of health geography by integrating social network analysis and spatial thinking to jointly investigate the influence of environmental and social spaces and to facilitate a more comprehensive understanding of the complex system of childhood obesity. It also extends existing models and provides a spatial agent-based model as an intervention exploration tool that can be calibrated for research and education by other scholars.
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