Why does marathon running in high humidity increase risk of exertional heat stroke, despite physiological thermoregulation?

💡 Explanation

High humidity reduces the vapor pressure gradient between the skin and the air, which dramatically reduces the efficiency of evaporative cooling from sweating. Because heat dissipation via sweat evaporation is the primary mechanism for cooling during intense exercise, this leads to heat stroke, therefore the cooling mechanism is overwhelmed rather than convection limitations.

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