Exercise in the heat series: The risks

Written by Jared Kauffman:

When talking about temperature regulation in the heat, there are a few things you need to be aware of about temperature and humidity. 

  • The body’s main defense against rising internal temperatures is to sweat. 
  • The evaporation of the sweat off the skin cools the body off. 
  • An issue occurs with this process when the temperature and/or the humidity are high enough that sweat does not evaporate.
  • At around 60 percent humidity, evaporation is inhibited, and around 80 percent humidity it stops altogether.


The most common dangers of exercising in the heat are dehydration from excessive sweating, and hyperthermia either from your body running out of sweat, or the humidity being so high that the sweat does not evaporate.   It is important to stay well hydrated!  When your body becomes excessively dehydrated, blood volume decreases so much that the circulatory system can stop working.  When the body cannot cool itself down, due either to dehydration, or a too high level of humidity not allowing the water to evaporate, heat stroke can occur.


There are three stages leading to heat stroke:

  1. Heat cramps - isolated or multiple muscle cramps or pains, and can be treated with fluids and moving into a cool environment.
  2.  Heat exhaustion - characterized by profuse sweating, slightly elevated body temperature, nausea, dizziness.  Heat exhaustion can quickly become heat stroke and should be treated as a medical emergency.
  3. Heat stroke - characterized by lack of sweating, very high body temperature, loss of consciousness, rapid and strong pulse.  If heat stroke is suspected, call 911 immediately. 

Ways to prevent heat illness:

  • Take time to become acclimatized.
  • Stay hydrated with water and some electrolytes,
  • Use the real feel temperature (combination of temperature and humidity) as your guide for exercising in the heat.
  • Wear loose fitted clothing.
  • Workout in a well ventilated environment. 


Stay tuned, next week, we’ll discuss hydration guidelines and the safest way to acclimatize to the heat.

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