Purpose Cities are applying reflective coatings on streets in an attempt to mitigate urban heat. These coatings are also being used to try to reduce heat stress during outdoor sports. This study models the progression of heat strain in elite marathon and race walk athletes competing on traditional dark asphalt, reflective pavement, or shaded asphalt in past and future Olympic Games [Tokyo (Sapporo), Paris, Los Angeles]. Methods Observed weather (Sapporo) or expected climate conditions for each city, along with modeled mean radiant temperature (TMRT) differences across the three surface types, were fed into the joint system (JOS-3) thermoregulation model. Resultant changes to heat strain parameters of core temperature (Tcr) and mean skin temperatures (Tsk), as well as skin wettedness and cardiac output, were modeled. Results Reflective pavement slightly increased the average TMRT (1.2-2.2 °C), which caused higher overall radiant heat loads on athletes and thus slightly higher (yet insignificant) Tcr and Tsk. These changes in simulated heat strain (worsening the situation) are the opposite of what is expected from a heat mitigation technology. Shading the athletes resulted in lower predicted Tcr (- 0.37 °C) and Tsk (- 0.68 °C) across events compared to sun-exposed asphalt, also decreasing cardiac output. Conclusion The minor increase in TMRT over reflective pavement transferred a negligible difference in simulated athlete heat strain over a 2-3 h intense competition. Overall, the large impact of solar radiation (even in the morning hours) should be decreased via design strategies that block the sun rather than strategies that increase radiant heat load.
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