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Training in the Heat

Author: Shane Brown, Director, head mentor and Senior Physiotherapist at The Physio Movement

Training in the heat

As we move into the hotter months of the year, it seems important to discuss the effects of training in the heat on performance, and how to best manage our training while in this environment. Learning to perform in the heat is a difficult task which has been well researched. This blog will focus on three main areas:

  1. What happens to our body during training in the heat
  2. How to manage our fatigue in the heat
  3. How to use heat to aid performance
  • What happens to our body during training the heat?

The effects of increased skin temperature and increased core body temperature alone and combined reduce maximal oxygen uptake, or what some know as VO2max. This, in simple terms, causes that specific exercise to become harder, and as we all know when a workout is more difficult, we can’t sustain it for as long.

For example:

Mr Green goes for a run at 5:00/km pace for 6km in 20deg Celsius heat, and finds it a lot easier than running at 5:00/km pace for 6km in 30deg Celsius heat.

Greater “relative intensity” essentially causes increased cardiovascular strain, which invariably makes our session feel harder perceptually to us. Therefore, constant-rate exercise is a lot harder to maintain and can only be performed for shorter periods or requires reduced pace. Most studies have found that maintaining a constant pace is more difficult due to increased strain, rather than mainly CNS fatigue (i.e. brain/spinal cord) or skeletal muscle metabolism.

Sweating is the way that we try and reduce our body temperature, and obviously this accelerates in hotter environments. Sweat losses therefore tend to exceed our fluid intake, and once we have lost greater than 2% of our body mass, dehydration becomes a further factor in heat stress. Dehydration works by reducing plasma volume and increasing hyperthermia, therefore further reducing VO2max.

For example:

Mr Green starts his run at 75kg and finishes at 73kg, meaning he was in relative dehydration at the end of his run and unable to keep up fluid intake. This impaired his performance.

Now, whilst there are mainly CV effects during heat training, there are certainly some CNS effects involved as well, which should be taken into consideration in extreme conditions.

So overall, in this brief summary of what happens to our body under extreme heat conditions, we can see that unfortunately we do have to alter our training during the warmer months. But in the end, there are ways we can use heat to our advantage as we

  • How to manage fatigue during the heat:   


The process of rehydration is impacted by a wide range of external and internal factors. Firstly, there is the degree of environmental stress – e.g. temperature, wind, humidity etc. Changes in these measures directly influence physiological changes, such as sweat rate. A study proposed that fluid intake rapidly increases above 25deg Celsius, with a large increase in environmental stress. Not only does environmental stress elicit physiological changes, but also psychological.

For example:

When going for a run and it is 35deg Celsius – do you prefer to have a cooler or a warmer drink to quench your thirst?

Also, there is the idea that athletes who have previous experience in rehydration and performing in the heat have a better understanding of how much fluid intake is required prior to dehydration occurring, therefore can be better equipped to manage their fluid intake. In addition, consider the beverage and it’s characteristics – whilst we would all love to be having a beer, this isn’t really the first thing we are thinking about to assist in rehydration on a run (in most cases). The taste, salinity, sweetness and other factors impact how much fluid we can and will consume in difficult conditions.

Pre-exercise Hydration

Athletes who perform a large amount of exercise can be chronically dehydrated, causing physiological changes such as increased cardiovascular strain and increased core temperature. The American College of Sports Medicine has recommended that 500mL of fluid be consumed at least two hours prior to exercise with adequate time for urination to ensure adequate hydration. Electrolytes through food and fluid also become important, due to the sodium loss within sweat, altering electrolyte levels. It has been recommended to maintain hydration better that we combine water with glycerol for improved effects

Rehydration during Exercise

Physiologically, rehydration helps dissipate heat and sustain cardiac output (among other things). Plasma volume is better maintained in the heat with rehydration than without, and also rehydration limits the hyperthermia (overheating) we experience in warm conditions. To manage fluid loss, most studies recommend simply trying to replace the amount of fluid lost through sweat, through rehydration. However, athletes often find this concept difficult, even though studies have shown that our bodies are able to tolerate this level of fluid. To make this concept easier, trial using different drinks with different tastes to make it more appealing. In addition, the stomach should always have about 400-600mL of fluid to maintain appropriate gastric emptying, with about 6-8% of this in carbohydrates (higher than this limits fluid absorption).

Rehydration following Exercise

In what may seem like an odd theory, studies show that water may not actually be the best fluid for rehydration following exercise. Consuming water alone decreases osmolality, which decreases the drive to drink and increases urine output. Including carbohydrates in your post-exercise formula can help with absorption. This will also come through your post-exercise meals in most cases. Whilst trying to replace sweat loss following exercise is great, you may still find yourself dehydrated using this formula. It has been suggested that aiming for 150% of weight loss with a high sodium content may be better for replacing fluid.

Using heat to aid performance:

Recently there has been fierce debate regarding the benefits of heat vs. altitude training. Everyone has seen their favourite athletes living it up in Europe or Falls Creek each year trying to get the benefits that altitude training gives. However, in more recent years, it has been found that heat training can also give us some benefits, with different effects. Below is a few tables adapted from Synergy Fitness which gives some insight into the benefits, recommendations and disadvantages of heat and altitude training.

Recommendations for Heat and Altitude training:


Altitude Training

Heat training

Optimal Range: 2000 – 2500m Temperature > 36C/Humidity >50%
21-28 days exposure 7-14 days exposure
Minimum 12-18hours/day 90-100min per day (short exposure) or every 3rd day (long exposure)
Exercise intensity appro 50% VO2 max


Benefits of Heat and Altitude training:


Altitude Training

Heat Training

Increased EPO, Red Blood Cell count/haemoglobin, lactate clearance, metabolism, oxygen to muscle Increased plasma volume, sweat sensitivity, blood flow to skin, endurance
Reduced lactate production Reduced HR during exercise, loss of salt in sweat
Maintained for 12-28 days Maintained for 10-28 days

Performance benefits of heat and altitude training:


Altitude Training

Heat Training 

Improved aerobic performance/CV fitness Increased aerobic capacity and cardiovascular efficiency
Improved repeated high intensity effort ability Maintained electrolyte balance
Increased fat loss Increased body internal cooling effect, and glycogen sparing
Increased recover rate

Disadvantages/Risks of Heat and Altitude Training:


Altitude Training

Heat Training

Doesn’t work for everyone Heat Illness
Altitude sickness Dehydration (acute and cumulative)
Training intensity may decrease due to greater energy demands Need to right temperature and humidity range to get the benefits
Increased impact on immune system


This information is designed to provide the facts for an informed decision. Different sports and environments will require different training methods. For example, if you are an athlete going to race in Kona, heat training could be beneficial to assist with your performance in the heat. While other endurance athletes may find more benefit from altitude training due to their prior experience in the area.

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