Non-linear relationships between outdoor thermal comfort and recreational walking among older adults in subsidized housing: Insights from Strava

Extreme heat worsens heat-health risks associated with outdoor physical activity, particularly regarding recreational walking by older adults. Recent literature has identified a non-linear relationship between outdoor air temperature and physical activity, but the role of outdoor thermal comfort, which reflects the total energy exchange between the human body and its surrounding environment, has rarely been quantified in this context. Moreover, while multifamily residential areas require specific built environment features to support safe walking, the thermal comfort levels within subsidized housing neighborhoods, which are critical for the mobility of older residents, remain poorly understood. This study utilizes crowdsourced Strava activity data to examine the non-linear associations between thermal comfort and older adults’ recreational walking across Harris County, Texas (July-September 2023). Human-environment energy exchange was estimated using the COMFA-OA heat stress model, which is specifically calibrated for older adults. By deriving month-specific thermal breakpoint from fitted non-linear response curves, we compared walking behaviors between street segments surrounding subsidized housing and a matched sample of apartment areas. Notably, across the study period, walking activity persisted into relatively high levels of thermal stress, including ranges classified as high heat stress under the COMFA-OA framework (>165 W/m ² ) and, in some cases, approaching the “dangerous” range defined by the original COMFA framework (>201 W/m ² ), potentially reflecting delayed risk perception and/or acclimatization. Furthermore, subsidized housing areas exhibited higher walking intensity in lower and intermediate thermal regimes, but this greater intensity vanished under high thermal stress, with walking counts converging to similarly low levels in both examined environments. All told, by linking age-specific microclimate stress with non-linear changes in walking activity, this study offers a novel framework for prioritizing heat-resilient street designs in socio-economically vulnerable neighborhoods.