Children’s physical activity during six weeks of school recess in hot weather: Associations with perceived and measured heat

Regular physical activity supports children’s health, yet extreme heat threatens outdoor movement opportunities during school, particularly in regions prone to hot weather. We examined fourth- and fifth-grade students’ self-reported physical activity and associations with perceived and objectively measured heat during outdoor recess across the first six weeks of the 2024–2025 school year in five elementary schools in the Phoenix Metropolitan Area (Arizona, USA), where temperatures frequently exceed 37°C. Students (n = 170) completed 981 brief paper questionnaires twice weekly post-recess, reporting activity intensity (sedentary, light, moderate-to-vigorous) and perceived heat (“not at all,” “a little,” “a lot”); air temperature data were collected from nearby weather stations. On average, 35% of students spent most of recess sedentary, 43% in light activity, and 23% in moderate-to-vigorous activity, with 45% of responses rated as the highest perceived heat category. Cumulative link mixed models showed activity levels did not change significantly over time. In perceived heat models, higher perceived heat was associated with increased odds of higher activity ( β = 0.89, SE = 0.34, p = 0.009); students who reported feeling “a little” or “a lot” hot were more active than those who reported being “not at all” hot. In objective heat models, higher temperatures were similarly associated with greater activity ( β = 0.20, SE = 0.10, p = 0.045). For each 1°C increase, the odds of reporting the next higher perceived heat category increased 8% (OR=1.078, 95% CI:1.01-1.15). Contrary to expectation, children did not reduce activity intensity in relation to heat; higher perceived and measured heat were instead associated with greater activity, highlighting a potential mismatch between behavior and heat-related risk. Proactive strategies like shaded areas, schedule adjustments, adequate hydration, and heat adaptation plans should be considered to safeguard children’s health. Future research should include device-based activity and physiological measures, longer observation periods, causal study designs, and additional youth age groups or thermal conditions to inform best practices.