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Exercise & Hot Weather

When you exercise, the working muscles in your body create heat, which is transported around the body by your blood.

  • As your body temperature increases, the blood vessels near the skin open up and the sweat glands work harder.
  • The body is cooled by the evaporation of sweat from the skin and the transfer of heat from the blood to the air.

In this way, the body tries to maintain its ideal temperature of 37°C.

Exercising in Hot Humid Weather

When the air is humid (already saturated with water), it limits the amount of sweat that can evaporate; instead, sweat just rolls off of your skin. When the air is hot, it does not cool the blood close to the surface of your skin. These conditions put you at risk of becoming overheated and dehydrated.


Fluid is lost from your blood when you sweat heavily while exercising in hot humid weather. When there is less fluid in the blood, your heart has to work harder to deliver blood and oxygen to exercising muscles.

Signs of overheating include:


Dehydration occurs when the body does not have enough fluid. Dehydration can occur in phases, with each phase becoming more serious.

There are 3 stages of dehydration.

Stage 1: Heat Cramps

Heat cramps may happen when you first start to become dehydrated.

Signs of heat cramps

  • ​Cramps in the calves and/or abdomen due to a loss of sodium from muscle cells.

Stage 2: Heat Exhaustion

Heat exhaustion can occur when you are exposed to high temperatures and you do not replace fluids.

Signs of heat exhaustion

  • ​Fatigue and weakness leading to dizziness.
  • Shortness of breath.
  • Nausea.
  • Vomiting.
  • Unsteadiness.

Stage 3: Heat Stroke

Heat stroke is a medical emergency. Heat stroke happens when the body’s temperature has risen to 39°C or higher.

Signs of heat stroke

  • Be unbalanced or unsteady on your feet.
  • Feel confused or disoriented.
  • Have bizarre behaviour.
  • Your body can no longer sweat!
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