Why does endurance performance decline in humid heat despite a constant core temperature near the hypothalamic set point?

💡 Explanation

Cardiovascular drift, where heart rate increases and stroke volume decreases over time, occurs because sweat evaporation is reduced in humid heat, thereby limiting heat dissipation. This places extra load on the cardiovascular system to maintain skin blood flow, therefore limiting oxygen delivery to working muscles, rather than changes in fuel metabolism or vasoconstriction.

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