Training in the Heat: 4 Tips to Avoid Collapsing!

June 28, 2018 , ,

It’s finally summer, we can strip off and train outside. But heat and humidity can have a negative impact on your performance if you are not careful. Here are four tips to help you avoid collapsing when you practice an outdoor sport this summer.

1. Slow down

It’s normal that your perception of effort during a similar training session increases when it’s hot. When we’re hot, blood is forced towards the skin to cool the body through sweating. This means that there is less blood available to transport oxygen towards muscles, which limits how much effort you can make. Heat and humidity can also slow down your recovery post-training, because your body will use its energy to cool down rather than to transport nutrients to the muscles. So, leave your GPS watch at home, start your workout slower than usual, and accelerate in the second half if you feel good. Your body needs one to two weeks to acclimatize to the heat. It will adapt by reducing its cardiac frequency and temperature and by increasing its sweat rate. Some studies suggest that training in hot weather, by creating adaptations, can enable you to improve your performance once the cooler temperatures return.

2. Hydrate

Hydrating properly is important, especially when it’s hot. Sweat enables you to lose heat and therefore to cool down. However, sweating is less efficient if the weather is hot and humid, and when we become dehydrated. It’s simple, the more dehydrated we are, the less we sweat, the hotter we feel and the more our performance diminishes! It’s important to begin your workout or competition well hydrated by drinking regularly. The recommendation is to drink around 5 to 7 ml of fluid per kilogram of body weight within the four hours before your workout or competition, and if your urine is still dark, to drink another 3 to 5 ml of fluid per kilogram of weight in the two hours before. During your workout, you need to drink regularly but respect your thirst and not drink too much. If your workout is longer than one hour, go for a sports drink. A drink that contains sodium and carbohydrates in adequate amounts allows a better hydration than water alone. However, a drink that contains too many carbohydrates (over 8%) can have the opposite effect by diminishing gastric emptying and therefore reducing the quantity of liquid available for absorption, and can also cause gastro-intestinal issues. It should be noted that when it’s hot and the skin’s temperature goes beyond 27oC, dehydration becomes a limiting factor to endurance performance. For each increase of 1oC, performance diminishes by around 1.5%. Therefore, proper hydration is essential when it’s hot. You should know that pouring water over your head has no beneficial effect on performance and doesn’t help the body to cool down, you’re better off drinking it!

3. Limit alcohol

If you were intending to have a few drinks the evening prior to your race, you should know that alcohol can impair your performance. Alcohol is a diuretic, which means it increases the production of urine and can cause dehydration. It also causes a reduction in antidiuretic hormone (ADH) and triggers the body to eliminate more water than it absorbs. What’s more, calories in alcohol are not used to produce energy and are not useful to athletes. Alcohol also impacts on the quality of your sleep, muscle and glycogen synthesis, and recovery. You should always avoid drinking alcohol before or after a workout or a race, but even more importantly when it is hot outside, since heat and alcohol will have cumulative effects on causing dehydration and poor recovery.

4. Establish a hydration plan

Water and sodium losses vary greatly from one person to another, so it’s important to prepare a personalized hydration plan and try it out before a competition. If you want to estimate how much fluid you need to drink before a race or sporting event, it’s important to know your own water losses and to aim to lose no more than 2% of your body weight during your competition. To do that, you can weigh yourself before and after a long run or workout and calculate your fluid losses.

Here’s an example of this calculation. My weight Sunday morning was 60.9kg. I ran 14km, didn’t drink anything and my weight post-run was 60kg. I therefore lost 0.9kg = 0.9L = 900ml. So, to replace this fluid loss, I need to drink a total of 900ml. I can estimate that if I run a marathon (around three times that distance) in the same conditions (speed and temperature), my water losses will triple, so 2.7L. I need to aim to lose no more than 2% of my body weight during my race: 00.2 x 60.9kg = 1.2 kg = 1.2L. So, during my marathon, I should drink at least 2.7L – 1.2L = 1.5L of fluid in total.


  • Burke et Deakin (2015) Clinical Sports Nutrition, 5th Edition, McGraw-Hill Education, 828 pages.
  • Tyler CJ et coll. (2016) The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Med; 11:1771.


Kathryn Adel
Kathryn holds a Bachelor Degree in Nutrition as well as a Bachelor and a Master Degree in Kinesiology, all from Laval University. She is a Registered Dietitian and active member of the Ordre professionnel des Diététistes Nutritionnistes du Québec (ODNQ) and of the American Academy of Nutrition and Dietetics. She holds the Monash University's certification for the FODMAP diet and IBS, and has considerable clinical experience in that area. She is also an accomplished athlete, having ran track and cross-country at a national level. Kathryn specializes in sports nutrition, weight loss, diabetes, as well as heart and gastrointestinal health.

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