Training in Heat: Basic Guidelines

Training in Heat: Basic Guidelines

It’s important to bear in mind certain basic considerations in terms of thermoregulation when training in heat.

Many athletes, particularly resistance athletes, don’t know how our body works and how it regulates body temperature.

By answering these questions, not only will you potentially dangerous health scenarios, but you’ll have optimal performance abilities in hot climate conditions and/or with a high humidity level.

Runners training heat

Before giving you the basic considerations to take into account when practicing sport in hot conditions, let’s look at how our body works from the point of view of thermoregulation.

Basic Physiological Concepts

The human body is nearly completely water.

It’s present in our body to very high percentages: 75% in the muscles, 83% in the blood, 75% of the brain, etc…

The water remains in its designated place to maintain a perfect balance in normal conditions, but if that water balance ruptured, a series of processes are triggered that put the health of the individual at risk, even reaching fatal circumstances.

The natural temperature of the body is approximately 37º.

In this sense, the internal organs are more active than the peripheral ones (metabolically speaking), reaching higher temperatures; however, the superficial tissues suffer greater temperature variation.

Factors affecting body surface temperature variation.

  • Intense exercise
  • Metabolic changes.
  • Environmental temperature/humidity.
  • Air currents.
  • Sweat.
  • Changes in subcutaneous flow.
  • Heat from radiation.
When exercising, there’s an increase in body temperature (producing up to 500kcal/hour, vs. 75kcal/hour at rest).


Hence that heat production has to be eliminated in order to maintain the body’s base temperature.

How does the Human Body eliminate Excess Heat?

The body uses up energy when eliminating excess heat, and will be affected by the above factors.

That is, in cases where this heat cannot be eliminated, or where climatic conditions make this process difficult, different patterns must be taken into account whose ultimate goal is to maintain that body temperature while maintaining the water balance.

Otherwise, there is a substantial decrease in sports performance.

The body normally rids itself of excess heat by sweating, which eliminates electrolytes (sodium, potassium, chlorine, calcium).

When training in heat, we should be conscious that one of the consequences of this loss of minerals is dehydration. If you want to find out more about this, have a look at this article.

Those electrolytes, distributed in the extra and intra-cellular fluid, maintain an optimal state, that hydric balance necessary for the correct functioning of the body.

Heat Regulation Mechanisms

It’s important to know how our body reacts when training in heat:


This is in charge of regulating heat in our body.

It acts as a “Thermal Sensor”, which not only receives but measures the temperature information in every part of the body. It integrates this information and activates the necessary mechanisms to control it.


One of the heat control mechanisms is to eliminate heat through sweat.

It’s useful for athletes to have basic notions of how to measure sweat loss in given environmental conditions and before an exercise: weight loss during sport, and fluid intake during sport.


Sweat is a mechanism for regulating body heat


We also have other mechanisms:

  • Radiation;
  • Conduction (to be taken into account when practising sports in water (swimming), or in contact with air, such as cycling);
  • And also Convection, Evaporation.

How much Water does our Body contain?

At Rest

As an indication, in a state of rest we have a total of 2.5 litres of water, and it can be determined that:

  • 250ml is used for Metabolism.
  • 750ml is ingested in food.
  • 1500ml is ingested in drink.
In the resting state, water loss occurs mostly through urine (up to 1500 ml), through breathing (700 ml), and finally through sweat and faeces.

During Exercise

As mentioned above, most of the energy expenditure produced during exercise is used to maintain body temperature (metabolic heat, 75%- 80%), and the rest is used for muscle work.

Because of this, you should bear in mind that metabolic expenditure takes on special relevance during sports practice, since our organism tries to constantly maintain its base temperature.

There are also other factors to be taken into account when maintaining that base temperature, such as environmental conditions: heat, cold, degree of humidity…

They directly affect how the body will produce heat to maintain that body temperature, and therefore for sports practice should be considered and studied for the hydration plan.

You sweat more in a hot and humid environment than in a cold one, and the water and electrolyte losses are different; and therefore the supplementation and hydration strategy is different.

What can be done to reduce this Metabolic Heat?

One way is through sweating.

By sweating, there’s a loss of liquids that must be replaced to maintain the water balance and homeostatic state of the blood plasma at all times.

In the case of sweating caused by intense exercise as well as high ambient temperatures, the amounts that can be lost through evaporation varies greatly, and can become very high (1.5-2 litres of sweat an hour).

It’s important to point out in relation to the heat loss produced when sweat evaporates that, if it does not evaporate, heat absorption and cooling of the skin does not take place. In other words, it is not the sweating itself, but the evaporation of that sweat.

Hydration with HSN

Without sweat evaporation, there’s no loss of sweat.

What happens in Humid Environments?

This is particularly relevant is humid environments, as the evaporation happens much slower and the internal body heat increases significantly.

In such event, it’s extremely important to cool yourself down: pour water on areas such as the wrists, the back of the neck…

If a good hydric balance is not kept, there is a:

  • Decrease in the plasma volume (see picture above)
  • Big increase in body temperature; and, therefore,
  • An increase in the amount of sweat as a thermoregulator;

How does Heat affect our Physical Performance?

Along with the other processes, it also increases the heart rate and, at the same time, greatly increases the perceived effort during exercise

All this, without a good water balance, will cause and enormous drop in performance.


It’s true that every individual has their own rhythm of sweating.

For women, the body generally sweats less, meaning the body temperature increases and and sensation of heat too.

That’s why it is recommended in resistance tests that women be kept well cooled, to reduce that feeling of heat and suffocation.

As set out by the ACSM (American College Of Sports Medicine) in 2007, when exercising, we should re-hydrate so as not to exceed a loss of more than 2% of our body weight.

When the loss is greater than 2% of our body weight, sporting performance suffers greatly.

Basic Advice for Training in Heat

Period of Heat Acclimatisation

Between one week and 15 days: control the volume and duration of training, and take special care with fluid intake (drinks that include sodium, potassium and magnesium).

Keep yourself well hydrated

A good indicator of optimal level of hydration is the colour of urine.

The clearer it is, the better hydrated you are.

Frequent cooling

It’s advisable to run in places where you can cool yourself down, doing so not only by drinking water but by lowering your body temperature by through water over your wrists, back of the neck…

Consume mineral salts according to the degree of sweating and duration of exercise.


  • Up to 60mins: it’s necessary to calculate the dose of isotonic drinks, as not only water should be drunk, but lost electrolytes should be recovered too.
  • Over 90 minutes: and if they are resistance tests, in addition to water they should contain not only electrolytes but also carbohydrates.

Hour of training

Try to take advantage of the coolest hours of the day for sports practice (especially for those high intensity sessions).


The heat produced through energy metabolism during exercise can be extremely high, and it’s eliminated through the skin by a number of mechanisms.

In a hot environment, the majority of heat is lost through sweat evaporation.

If the environment is also humid, the evaporation of sweat and the elimination of heat is minimal, and a progressive hyperthermia can occur.

With the progressive dehydration due to the loss of sweat, there’s an increase in the internal temperature and a limitation in the cardiocirculatory system.

Run heat

In addition, during exercise, the body needs to carry blood to the skin as a thermoregulatory system.

As such, maintaining an optimum level of hydration prior to training, as well as maintaining a water balance during exercise, are indispensable factors in delaying the onset of fatigue, maintaining an optimum performance level, and avoiding health and/or medical problems caused by an excess or lack of electrolytes.

Bibliographic References

  1. Armstrong L.E., Maresh C.M. “The induction and Decay of heat acclimatisation in trained athletes”, Sports Medicine 12 (5):302-312, 1991.
  2. Haymes E.M.,Wells C.L. “Environment and Human Performance” Humena Kinetics Publishers, 1986.

Related Entires

  • For Heat Training, a Glycerol Supplement will help maximise Hydration. We tell you everything you need to know at this link.
  • Do you know the importance of replacing mineral salts? We invite you to go deeper by clicking here.
Review of Training in Heat

Basic physiological concepts - 100%

Regulating body temperature - 100%

Advice - 100%

Conclusions - 100%


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About Isabel del Barrio
Isabel del Barrio
Sport runs in the blood of Isabel, which she has proven since she was very little up until now. She wants to share that passion with all those who are passionate about sports.
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