Lower youth steps/day values observed at both high and low population density areas: a cross-sectional study in metropolitan Tokyo

BACKGROUND: Physical activity among children and adolescents (collectively, youth) is important to ensure adult health. Population density is a factor that affects physical activity via various environmental factors. However, the relationship between population density and physical activity among youth is not fully understood, especially in extremely high density area. The aim of this study was to examine the relationship between population density and physical activity of youth using pedometer-determined step data. METHODS: A total of 13,688 youth between 6 to 15 years of age were identified from the 2011 Tokyo Metropolitan Survey of Physical Fitness, Physical Activity and Lifestyle. Participants were divided into five subgroups according to the population density of their municipality of residence. The population density’s fixed effects on in-school, out-of-school, and daily total step count adjusted for gender and school grade were estimated. RESULTS: The lowest (< 2500 people/km(2)) and highest (> 10,000 people/km(2)) population density subgroups had significantly lower daily total step count and out-of-school step count than those of the reference population (5000–7500 people/km(2)). In contrast, in-school step count did not significantly differ according to population density. CONCLUSIONS: Both low population density and also high population density were related to lower step count. Low physical activity in high density areas has not been well documented in previous research. Considering population growth in urbanized area globally, these results suggest the importance of continued research of physical activity determinants in high population density areas. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12889-018-6028-y) contains supplementary material, which is available to authorized users.