Why running in the heat can be a real danger and how to optimize the training

Can we run in hot weather? Yes, the trainings can be continued in summer, you just need to know how to do it. The “art” of running in the heat is more than just drinking enough water. In such conditions it is necessary to remember that training begins not from the first step, but much earlier.

Running in the heat: risks

Running in the heat – sauna-like environment can be a serious health risk. Usually the blood flow (consisting mainly of water) cools the body. The flow reaches the sweat glands located on the skin. They form drops of sweat that transmit heat to the outside of the skin, where they evaporate. “These drops are like small containers for heat,” says Dr. Douglas Casa of the University of Connecticut.

When you are running in the heat, the organs and muscles need more blood than usual, which complicates the cooling system. The situation is further exacerbated by high humidity, as it limits the evaporation of sweat. And as if that isn’t enough, the body in case of hard running in the heat quickly dehydrates so that the blood becomes less liquid.

problems of running in the heat

When the body temperature reaches 40 degrees Celsius, the risk of heat stroke begins to increase dramatically. Continued intensive efforts in this situation can lead to the fact that the cardiovascular system will stop its thermoregulation function. Hyperthermia will weaken the heart, disable the kidneys and liver, and lead to cell damage. So a light heatstroke is done.

There is the article of “The neurological and cognitive consequences of hyperthermia” there the high body temperature risks are described.

If the temperature exceeds 40.5 ° C for more than 30 minutes, the enzymes in the body change their conformation, other proteins, no less important for our body, begin to curdle, and because of this, the entire metabolism strays, which leads to disorders in the organs, sometimes fatal. Moreover, it affects the brain tissue. At temperatures above 40 degrees, there are changes in the physical properties of nerve cells, and accordingly. They cease to perform their functions. Neurons of the brain in the transition through the “critical” temperature die instantly and irreversibly. All this leads to the death of the brain and the man. Read about it at

Different reactions to the heat

The situation is further complicated by the fact that everyone reacts differently to the load while running in the heat. The average body temperature at rest is less than 37 ° C. the norm during running in the heat at high temperatures is 38-39 ° C.  But with this temperature some people may feel worse, while others will be great.

When the body begins to produce more heat than it is able to neutralize, the reactions of the body may be different. You have to watch them carefully.

sick while running in the heat

“Dizziness and headaches, nausea, painful cramps , severe fatigue , the feeling that everything seems heavier than usual – signals that you can not ignore. The body struggles hard to cool down and you shouldn’t force it to train,” he says. Dr. Douglas Casa. The best solution in this case is to stop the training and relax in shade.

What to do if feel bad while running in the heat?

Heat stroke and other overheating-related problems while running in the heat can be prevented. All you need to do is to listen to the signals your body. However, if you had not pay enough attention and became ill, you must take the measures described below.


Painful spasms that occur during or after intense exercises.

  • Cause: muscle fatigue, loss of water and sodium
  • Symptoms: dehydration, cramps, fatigue
  • What to do: massage, drinking water


Overload of the circulatory and cardiovascular system and depletion of energy resources make it impossible to continue the training.

  • Cause: overload in hot and humid environment, dehydration
  • Symptoms: fatigue, irritability, nausea
  • What to do: relax in the shade with your feet up, applying ice, drinking plenty of water

what to do when feel bad running in the heat

Heat stroke

Danger with a body temperature above 40° C.

  • Cause: high temperature overload lasting more than an hour, usually in poor physical condition.
  • Symptoms: hyperventilation, confusion, dizziness, nausea
  • What to do: full immersion in cold water (2-15 ° C) for 30 minutes

Loss of consciousness

Fainting, occurring at high temperatures, most often in the first days of hot weather.

  • Cause: sudden stop immediately after intense exercise can cause blood to flow to the legs to the detriment of other organs, particularly the brain
  • Symptoms: dizziness, tunnel vision, pallor, weakness, low heart rate
  • What to do: lie in the shade with your feet up, drink a lot

How to optimize your training according to the weather forecast

Heat (above 30C) + low humidity (less than 30%)

  • Risk: the cooling system directs blood to the skin, which reduces the amount of blood in the muscles.
  • Solution: reduce the training by 20%.

Heat (above 30C) + high humidity (above 60%)

  • Risk: increased body temperature, dehydration – less blood liquid, humidity prevents sweat evaporating.
  • Solution: cut down the training, running at lower speed or goinig to the gym.

how to running in the heat

Water replenishment: test

Do not act at random, just count how much you need to drink water. Proper hydration means you have to replenish what’s gone with sweat while running in the heat. To determine the amount of liquid lost per hour:

  1. Weigh yourself.
  2. Run at a starting pace for an hour and pay close attention to how much you drink during that time.
  3. Weigh yourself again.
  4. Subtract the weight after the run from the weight before it.
  5. Add to the result the amount of liquid drunk (provided that 1 liter is 1 kilogram). If you weigh 0.5 kg less and drink 0.5 liters of water, the total loss of fluid was 1 liter.
  6. The test determines the fluid loss in the conditions relevant to a particular situation. So you can repeat it in different weather, temperature, humidity and see how the changes affect sweating.


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