I’ve published an old version of this article in another website. The following is an updated version with additional references and information. Let me know if you would like to have access to any of the full paper in the references.
…….
It is a known fact that heat stress impairs aerobic performance and high temperature and humidity affects endurance performance negatively.
Some athletes may be affected more than others. Possible factors contributing to individual athlete response to heat response and acclimation are listed below (Casadio et al 2016):
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 accessible to the elites, but there are still some take-aways that we can use.
In the recent “Heat stress and sport performance” conference, Mujika (2015) divided the heat management strategies into the following categories:
-
- pre-cooling 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 out come which is “to enhance well trained athletes’ endurance performance in hot environments”.
Pre-cooling Strategies
Pre-cooling 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).
Pre-cooling 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 exercise.
It is currently the most effective method of pre–cooling 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.
- whole body cold water immersion : 30 mins at a water temperature 22-30C or lower body cold water immersion: at lower temperature 10-18C.
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 slight 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-days 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.
(Racinais et al 2015)
(Heavy sweaters can add 3.0g of salt to 0.5L of a carbohydrate–electrolyte drink , prior to and post training/competition to maintain sodium balance).
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, you can try to increase sodium supplementation to 1.5g/L of fluid if it is sodium-related.
Note: 1g salt ~ 400mg sodium, 1 tsp salt ~ 5g salt ~ 2000mg sodium
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 (taken from respective websites)
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”.
General guideline for proper hydration post-training is to replace 150% of body mass losses within 1 hr of exercise, 100-120% more realistic, through consumption of fluids with foods (salty foods) – carbs, proteins, sodium
Heat acclimatization/adaptation strategies
Heat acclimatization/adaptation strategies include passive and active acclimatization strategies that can raise body core temperature, skin temperature and sweat rate. Note that this has to be done repeatedly before the race and is considered essential for athletes participating in any event in a hot condition.
Passive acclimatization strategies involve any “passive environmental heat exposure” such as taking a sauna.
Active heat adaptation ideally would involve training in the similar hot and humid condition you will be racing in (“acclimatization”). If that is not possible, training indoor in a simulated hot condition will also work (“acclimation”).
Ideally, each acclimatization session would last at least 60mins/day (90mins is ideal or 2h broken into two, 1 hr exposures) for at least 2 weeks to induce the physiological adaptation required. It would take at least 1 week for the body to obtain the main physiological adaptations, but early adaptation will start as early as the first few days.
Of course individual adaptations will vary, with adaptations developing more quickly in highly trained athletes. The more aerobically fit athletes can induce heat acclimatization faster (as much as 50%) and retain its benefit longer.
During the heat acclimatization period, the body will continually adapt. Increasing the duration and/or intensity should be considered in the heat-training strategy.
For those living in temperate climate or do not have the opportunity/time to train in the heat for acclimation purposes, taking a hot bath (40C) for at least 15mins immediately after training has been shown to elicit heat adaptation response in endurance runners. (Zurawlew et al, 2016) The duration of hot bath should be increased by 5mins daily up to 40mins for at least 6 consecutive days.
Interestingly, heat acclimatization strategies have also been proven to increase racing performance in neutral conditions. It is possible to use heat acclimatization training as another training stimulus for experienced athletes to improve performance. Note that for beginners, training quality should not be compromised and be substituted with heat training.
A mixed high intensity sessions with a duration of 60 minutes each (at least 5 sessions) may improve aerobic-based performance in hot and temperate conditions. Peak anaerobic performance does not seem to be enhanced by this. (Charlmers et al 2014)
Both pre-cooling strategy (cold water immersion 20mins prior) and cooling strategy during event (cold water spray, 3x every 1km) have been shown to improve performance in a 5km running time trials performed on 9 trained runners, racing in 33C. (Stevens et al 2017)
Humid vs dry heat
Cooling takes place via evaporation of sweat. Another strategy that has not been proven to be successful but has a potential to be tested in a long distance event is “wearing sweatbands soaked in alcohol or menthol based liquid solution”. The increased rate of evaporation may contribute to a cooling effect on the skin.
References
Mujiko I, 2015, “Case studies about elite performance in the heat” <.http://www.inigomujika.com/en/2015/07/case-studies-about-elite-performance-in-the-heat>
You must be logged in to post a comment.