Association of indoor thermal environment with children’s physical activity in summer and winter

Indoor environments play an important role in children’s health and behavior, yet the impact of thermal environments on physical activity remains insufficiently understood. This study investigated the association between indoor thermal environments and children’s physical activity in summer and winter in Japan. Detailed indoor thermal measurements and objective accelerometer data were collected from 26 children aged 4–12 years, each measured in both seasons under parental supervision to ensure data quality. Significant associations were found between temperatures in living areas and physical activity intensity. Warmer indoor environments in winter were associated with higher activity intensity, whereas cooler indoor environments in summer were associated with lower activity intensity. A new indicator, the seasonal activity ratio (SAR), defined as the ratio of winter to summer activity intensity, was developed to assess the degree of seasonal variation. The SAR showed an overall seasonal decline (mean SAR: 0.96 ± 0.06). Children living in homes where non-living areas maintained cooler environments in summer and warmer environments in winter exhibited significantly smaller seasonal declines in activity compared with those in other environments. These findings demonstrate that even in modern, high-performance homes, a thermal design strategy is required that addresses both living and non-living areas in order to promote children’s physical activity year-round and to mitigate typical winter declines. The results of this study provide objective evidence to inform residential design and policies aimed at fostering healthier indoor environmental quality for children. • The indoor thermal environment is associated with children’s physical activity. • Warmer indoor environments in winter are linked to higher physical activity levels. • Cooler indoor environments in summer are linked to lower physical activity levels. • Seasonal activity ratio is used to assess seasonal variation in activity. • Thermal environments in non-living areas help mitigate winter declines in activity.