Why does endurance performance decline sharply when ambient temperature rises above the thermoneutral zone during a marathon?

💡 Explanation

During exercise in high ambient temperatures, peripheral vasodilation occurs to dissipate heat via convection. This cutaneous vasodilation reduces blood flow and thus oxygen delivery to working muscles, because blood is redirected away from the muscles to the skin for cooling; therefore, endurance declines, rather than because of glycogen depletion or lactate buffering.

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