Is working out in the heat really dangerous?

Can heat actually be harmful?

In short, yes! Heat can be harmful and even be deadly if you do not take the necessary precautions.

What happens when you exercise?

The temperature of our deeper tissue is in a dynamic balance between heat loss / gain. If because of exercise or external influences this equilibrium is interrupted the core temperature rises. In elite athlete the temperature can raise by 1.8° F / 5-7 min if exercising at intense aerobic levels.
Your body cannot let this go on indefinitely without taking damage therefore regulatory processes take place.

Ways of transferring heat away from the body

  1. Radiation (we radiate electromagnetic heat waves through the air to solid cooler objects in our environment)
  2. Conduction (is the heat transfer directly from one molecule to another, hand to air, or hand to water for example)
  3. Convection is dependent on the air or fluid exchange surrounding our body. If the air does not move, it functions as insulation after heating up to body temperature. This is the reason why a fan works so well :-).
  4. Evaporation is the major player in the fight against overheating. Water vaporizes from the respiratory passages and skin surfaces which continually transfers heat to the environment.

How does your body activate its cooling mechanisms?

We have an increased circulation to our face and skin in general. in extreme heat 15-25% of our cardiac output goes to the skin. This increased blood flow improves our ability to give heat off to air molecules.

Sweating starts within a couple of seconds of intense exercise. It takes about 30 min before it reaches an equilibrium  with the exercise load. The increased circulation combined with the effects of conduction and evaporation lead to cooled blood flowing back to the core and taking on more heat to transport off. Additionally hormonal changes regulate down the salt content in sweat which prevents early onset of cramping.

What happens when it is hot and humid outside?

In high temperatures radiation (emitting heat waves) , conduction (molecule to molecule) and convection (air heating and it’s replacement) won’t work anymore. If the outside temperature is higher than the core temperature you might actually gain heat from those three.

Now if humidity comes out to play it gets even worse. Now we have another problem. Humidity will take out our major player, Evaporation.  The air around us is more saturated with water and our sweat will no longer evaporate. Instead it will run down without having a cooling effect and we run into the danger of overheating and dehydration. Individuals are actually capable of resisting relatively high temperatures as long as the relative humidity is low.

What effect does your clothing have?

Changing from wet to dry clothing actually does not help. dry clothing usually slows down heat exchange. Moisture wicking clothing can help to optimize heat transfer especially in intense exercise during hot weather.

If you ignore the heat

Bad things will happen if you ignore the heat. Your performance drops because huge amounts of blood are diverted to cool you off. Renal and liver complications are common during exertional heat stress. The core temperature raises to dangerous levels which reduces the drive to exercise leads to fatigue in order protect your body from damage.

How does it show?

Heat cramps, heat exhaustion (weak, rapid pulse, headache, dizziness, general weakness) and heat stroke (failure of heat-regulating mechanisms) are a clear sign of overheating In case of a heat stroke the circulatory system collapses (absence of sweating, altered mental status) and a person can die. Medical intervention is crucial. The person should replace fluids, be cooled down by ice packs to the neck area.

I know the summer is almost over but we are still having hot days

Woman is receiving help after having a heatstroke

You don’t want to be caught unaware by the heat

. So please pay attention. No training session is worth risking your health or life. Cut the training short, choose to change the location or ease off.

Have an awesome day,


McArdle et al. (2007). Exercise Physiology – Energy, Nutrition & Human Performance. 6th Ed. Lippincott Williams & Wilkins.

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