Strategies to improve endurance racing in the heat – Part 1

Strategies to improve endurance racing in the heat – Part 1

by Elvia Suryadi

It’s a known fact that high temperature and humidity affects endurance performance negatively. Some athletes may be affected more than others. What are the strategies that can be implemented to minimize the negative impacts of racing in the heat?

In this article I am providing you a summary of the latest research on strategies to improve endurance performance in the heat.
Not only have all these strategies been tested in the labs, many are currently used by elite athletes and sports teams around the world.
Some of these strategies may seem to only be accessible to the elites, but there are still some take-aways that we use.

In the recent “Heat stress and sport performance” conference, Mujiko (2015) divided the heat management strategies into 3 main categories:

  • precooling interventions – during race
  • optimal hydration practices – before, during and after exercise/race
  • heat acclimatization/adaptation – before race, to prepare athletes coping with heat stress

Each strategy works differently with the same outcome which is “to enhance well trained athletes’ endurance performance in hot environments”.

Precooling Strategies

Precooling strategies include any strategy that can help to lower body core temperature BEFORE exercise. It can be further divided into skin-cooling (which will reduce cardiovascular strain during exercise) and whole-body-cooling (to reduce organ and skeletal muscle temperatures).

Precooling has been proven to improve endurance performance and prolong endurance capacity in hot condition.

Some of the applications include:

  • whole-body cold water immersion : 30 mins at a water temperature 22-30C or lower body cold water immersion: at lower temperature 10-18C. This will definitely help to lower body core temperature but at the same time cooling the muscles which may not desirable before race. It is currently the most effective method of precooling to improve endurance performance in hot conditions, if muscle cooling is not an issue.
  • using cooling garments: iced towel or special cooling packs or vests. Fanning and staying in a cold room will also help. This is ideal for skin-cooling strategy which reduces skin temperature without reducing muscle temperature.
  • drinking cold water. Interestingly, cold water could improve performance if ingested before but not during exercise.
  • drinking ice-slushy. This method is proven to be more efficient in cooling prior or during exercise than drinking cold water. It is also the second most effective method after whole-body cold water immersion.
  • mixed methods of any of the above.

Hydration Strategies

Hydration strategies are something that we often associate with race day hydration. Maintaining and practising hydration strategies during training is essential to maintain fluid balance before the race.

The latest recommendation to maintain adequate hydration status is for athletes to consume 6mL of fluid per kg of body mass every 2-3 hr before training or racing in the heat.

Another interesting note: If you ever consider losing some (water) weight before your cycling race in order to gain a higher power-to-weight ratio, don’t. Mijuko pointed out that such “benefit” is more detrimental than “dehydration-induced hyperthermia” or having an increased body core temperature due to dehydration.

The notion of dehydration leads to reduced performance has not been conclusively proven. The latest finding by Cheung, et al (2015) states that 3% body mass loss due to dehydration-induced hyperthermia does not lower hydration status nor perception of thirst in the “sustained submaximal exercise performance in the heat for a healthy and fit population”. Current recommendation still stands that up to 2% of body mass loss due to dehydration does not hinder any aerobic performance. Drinking to thirst is highly recommended for most endurance events, unless you are taking part in a very hot long distance event or multi-day events. Daily morning body mass and urine colors may be used to monitor dehydration status.

Athletes training in the heat have higher sodium requirements than the general population. Heavy sweaters may increase sodium (salt) intake prior to and after hot weather training and racing. (The recommended intake is to add 3.0g of salt to 0.5L of a carbohydrate-electrolyte drink).

For exercise longer than 1 hr, you should aim to consume a solution containing 0.5-0.7g/L of sodium. If you are prone to muscle cramping, it is recommended to increase sodium supplementation to 1.5g/L of fluid.

When calculating your sodium intake on race day, you should consider ALL intakes (from gels/drinks/tablets/bars). Below is the sodium composition of some popular electrolyte tablets.

Product   Composition
Carb g/100ml Sodium
High 5 Zero Electrolyte Tablets 1 effervescent tablet added to 750ml fluid negligible 0.2 g/tablet
High 5 Zero Electrolyte Extreme Tablets 1 effervescent tablet added to 750ml fluidContains 65mg caffeine negligible 0.2g/tablet
Nuun 1 effervescent tablet added to 500ml fluid negligible 0.36g/tablet
Shotz Electrolytes 1 effervescent tablet added to 500ml fluid negligible 0.43g/tablet
Salt StickCaps 1 capsule 0 0.215g/capsule

Some studies have shown that hyperhydration (or overhydration) “prior to prolonged exercise in the heat” might be beneficial. It is something you can consider in training and see if it works out for you.

Over-hydration should be avoided in races as it may result in “water intoxication” or hyponatraemia that has very serious consequences.

One interesting hydration strategies mentioned is glycerol hyperhydration. It involves adding glycerol to the water consumed (before and during race) whose purpose is to increase water content in the body. This method does not seem to decrease the body core temperature but some studies showed that it decreases the water loss that often leads to dehydration.

Glycerol is chemically an alcohol, technically a sugar alcohol. It is a component of stored fat (triglycerides), is present naturally in blood plasma as free glycerol and is obtained from oil or fats. Analysis of some studies in this area indicates that “endurance athletes intending to hyperhydrate with glycerol should ingest glycerol 1.2 g/kg BW in 26 mL/kg BW of fluid over a period of 60 minutes, 30 minutes prior to exercise”

That’s all for now. I will continue with Part II to talk about rehydration, heat acclimatization and some practical recommendations.


Cheung SS, et al, 2015, “Separate and combined effects of dehydration and thirst sensation on exercise performance in the heat” Scandinavian Journal of Medicine & Science in Sports, May, vol.25, Suppl, pp 104-111

Jones P, et al, 2012, “Pre-cooling for endurance exercise performance in the heat:: a systematic review” BMC Medicine, vol 10 no 166

Mujiko I, 2015, “Case studies about elite performance in the heat”<>

Racinais S, et al, 2015, “Consensus recommendations on training and competing in the heat” British Journal Sports Medicine, Jun, vol.0, pg 1-10

Rosendal SP, et al, 2012, “Guidelines for Glycerol Use in Hyperhydration and Rehydration” Sports Medicne, Oct, vol 40 no 2, pp.1130139

Stevens CJ, et al, 2013, “Ice slurry ingestion during cycling improves Olympic distance triathlon performance in the heat” Journal of Sports Sciences, vol 31 no 12



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