Dose-response associations between a walkability index and adults' domain-specific walking: A study of 95 cities in Japan

We examined dose–response relations between a Japan Postcode-level Walkability Index (JPWI) and total walking, walking for leisure; and walking for transport, among adults living in 95 cities across the country. This nationwide cross-sectional study included 40,286 adults (males 50.5%, 49.4 ± 15.6 years) residing in a wide range of urban and rural settings, who responded to a web-based survey conducted in 2021 using quota sampling. The JPWI was calculated by generating a 1000 m road network buffer from a representative point within each postcode boundary using the mean of z-scores summarizing the population density, intersection density and number of destinations within this buffer. JPWI scores ranged from −1.848 to 2.590. There was a non-linear positive association between JPWI and total walking, with an inflection point at a JPWI of 0.78 (95% CI: 0.69, 0.87), below which the association with walking time was minimal (B = 22 [11,32]), but above which walking time increased significantly (B = 118 [106, 129]). Similar patterns of associations were observed in both leisure walking and walking for transport, with inflection points at JPWI values of 0.78 (95% CI: 0.69, 0.86) and 0.64 (95% CI: 0.42, 0.86), respectively. Findings highlight the potential utility of considering how the JPWI (and potentially related measures for other countries) of local areas compare with such empirically-identified inflection points when developing strategies for improving the built environment to promote physical activity.