Every race requires a bit of planning but racing in the heat requires a bit more thought. When the ambient temperature is extremely high and your working muscles are generating additional heat, it's very important to externally keep your body cool and to replenish what you lose from sweat. During a race, when your metabolic and heat production rates are high, core temperature increases. This isn't too much of a worry in cool conditions but if it's hot and humid outside, the body then has to cope with the environmental heat and the heat produced by the working muscles. To keep you from overheating, the first priority of your body is sending more blood to the skin to help with cooling – leaving less oxygen-rich blood for the muscles and less blood for your gut to help with digestion. As a way to help cool yourself, your body increases the sweat rate to remove heat from your body through evaporative cooling. As you become dehydrated (from water loss), blood volume decre...
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