While physical activity is critical to human health, most people do not meet recommended guidelines. More walkable built environments have the potential to increase activity across the population. However, previous studies on the built environment and physical activity have led to mixed findings, possibly due to methodological limitations such as small cohorts, few or single locations, over-reliance on self-reported measures, and cross-sectional designs. Here, we address these limitations by leveraging a large U.S. cohort of smartphone users (N=2,112,288) to evaluate within-person longitudinal behavior changes that occurred over 248,266 days of objectively-measured physical activity across 7,447 relocations among 1,609 U.S. cities. By analyzing the results of this natural experiment, which exposed individuals to differing built environments, we find that increases in walkability are associated with significant increases in physical activity after relocation (and vice versa). These changes hold across subpopulations of different genders, age, and body-mass index (BMI), and are sustained over three months after moving.The added activity observed after moving to a more walkable location is predominantly composed of moderate-to-vigorous physical activity (MVPA), which is linked to an array of associated health benefits across the life course. A simulation experiment demonstrates that substantial walkability improvements (i.e., bringing all US locations to the walkability level of Chicago or Philadelphia) may lead to 10.3% or 33 million more Americans meeting aerobic physical activity guidelines. Evidence against residential self-selection confounding is reported. Our findings provide robust evidence supporting the importance of the built environment in directly improving health-enhancing physical activity, in addition to offering potential guidance for public policy activities in this area.

翻译：尽管体力活动对人类健康至关重要，但大多数人未能达到推荐标准。更具步行适宜性的建成环境有潜力提升全民活动水平。然而，先前关于建成环境与体力活动关系的研究结论不一，可能源于方法学局限，如样本规模小、研究地点单一或稀少、过度依赖自我报告数据以及横断面设计。本研究通过利用美国大规模智能手机用户队列（N=2,112,288），评估了在1,609个美国城市中发生的7,447次搬迁事件期间，跨越248,266天客观测量体力活动数据所呈现的个体纵向行为变化，从而解决了上述局限。通过分析这一使个体暴露于不同建成环境的自然实验结果，我们发现步行适宜性的提升与搬迁后体力活动的显著增加相关（反之亦然）。这些变化在不同性别、年龄和身体质量指数（BMI）的亚群体中均成立，并在搬迁后持续三个月。搬迁至步行适宜性更高地区后观察到的额外活动主要由中等至剧烈体力活动（MVPA）构成，这与生命全程中一系列相关的健康益处相关联。一项模拟实验表明，显著的步行适宜性改善（例如，使美国所有地区达到芝加哥或费城的步行适宜性水平）可能使额外10.3%或3,300万美国人达到有氧体力活动指南标准。研究还报告了反驳居住自选择混杂效应的证据。我们的发现为建成环境在直接促进健康增强型体力活动方面的重要性提供了有力证据，并为该领域的公共政策活动提供了潜在指导。