Heat, Altitude: Challenges and Opportunities Presented by Environmental Constraints for Athletes
What will the temperature be like during the 2024 Paris Olympic Games? With global warming, the number of sporting events taking place during summer heat waves is on the rise. Athletes’ exposure to heat is also increasing as new nations host major competitions in hot regions, such as Qatar for the 2019 World Athletics Championships, the United Arab Emirates for the 2022 World Triathlon Championship Series final, and Senegal for the 2026 Youth Olympic Games in Dakar.
Jonathan Rubio, University of Montpellier
While specific protocols and regulations are beginning to emerge within various international federations that allow for the cancellation or modification of events in the event of extreme conditions (the most recent example being the Rugby World Cup match between France and New Zealand, during which cooling breaks were taken midway through both halves), athletes must also prepare specifically for the heat; otherwise, they risk impaired performance in endurance sports, or even medical problems—including, in some cases, death from heatstroke.
When preparing for a major sporting event, endurance athletes such as triathletes typically spend several weeks training at high altitude: since the 1968 Olympic Games in Mexico City, the benefits of high-altitude training have been scientifically documented. The main expected benefit is improved performance through an increase in hemoglobin levels, which allows for better oxygen transport throughout the body and to the muscles, thereby contributing to energy production in the muscles.
However, before a competition in hot conditions, it is necessary to undergo additional specific preparation, which involves spending time in those same conditions—or at least training in them—to not only help the athlete cope with the heat as effectively as possible but also to protect the athlete's health.
Environmental stressors during training can be beneficial… if used properly
Incorporating environmental stressors such as heat or altitude into training plans is not without consequences. In fact, when coaches plan training camps for athletes that include environmental stressors, these stressors are added to all other types of stress, particularly that related to training load. For example, excessive heat stress or hypoxia without adjusting training intensity and volume can undermine the expected benefits. Indeed, too much physiological stress leads to fatigue, which prevents the body from adapting.
Today, to ensure that competition preparations go smoothly, athletes are closely monitored, and their condition is tracked using various physiological parameters.
Training for Competitions in Hot Conditions
When it comes to heat, athletes train under natural or controlled conditions. In other words, in a room specially designed for hot environments, where athletes perform their exercises, ranging from weight training to cycling on a stationary bike or running on a treadmill.
This involves quantifying the desired heat stress, that is, both the target temperature and humidity (generally around 38 °C and 50% humidity). The recommended daily heat exposure is relatively low, ranging from 60 to 90 minutes per day for daily training.
The athletes are given capsules to swallow several hours in advance so that their body temperature can be monitored in real time. This allows for better control of the risk of heatstroke and ensures that the hyperthermia necessary for cellular adaptations to occur is present (the goal is to maintain an internal temperature of 38.5 °C for more than 30 minutes).
Other physiological parameters specific to heat acclimatization are monitored, such as sweat rate and urine specific gravity to ensure there is no excessive dehydration, electrolyte losses ([Na+], particularly useful information in long-distance events to compensate for losses with sodium-enriched intake), hematocrit level (the volume of red blood cells in the blood), as well as exercise heart rate, the latter reflecting the overall state of acclimatization.
Perceptual metrics based on sensory scales of comfort and thermal sensation are also recorded for each session.
Training with Less Oxygen: A Textbook Example of the Need to Tailor Protocols to the Individual
Determining the appropriate intensity for hypoxia training is far more complex and requires much greater caution than heat training in order to achieve results, especially among endurance athletes who already have a very high hemoglobin mass. While exposure time is limited in heat training, the goal in hypoxia training is, on the contrary, to spend much more time in hypoxic conditions.
In the past, there was a tendency to refer to athletes as “responders” or “non-responders” to hypoxic stress (meaning that some do not produce additional red blood cells after being exposed to a hypoxic environment), whereas we now know that an athlete who is a non-responder at a certain altitude and with a certain training regimen can become a responder by adjusting the hypoxia dose—that is, either by increasing the exposure time at the same altitude or by maintaining a similar exposure time but at a higher altitude. But things aren’t that simple… because the dose must be increased for some and decreased for others.
This individualized adaptation to hypoxic stress conditions helps optimize erythropoietic responses (i.e., red blood cell production). It is for this reason that endurance athletes today can sleep at a higher altitude than their home environment, thanks to hypoxic chambers. Constant adjustments are made to the altitude settings in these chambers to control the amount of daily hypoxic stress induced, thereby managing the athletes’ fatigue levels as effectively as possible.
These athletes receive equally specific monitoring, particularly using pulse oximeters that record theirO2 saturation levels overnight. For example, when preparing for a competition that will take place immediately after the training camp, it is estimated that an average oxygen saturation level of 90–91% (compared to 100% at sea level) is sufficient to induce altitude-related adaptations without causing excessive fatigue.
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During the acclimatization phase (between 3 and 8 days), training intensity is kept to a minimum. Overall fatigue levels are assessed each morning through an analysis of heart rate variability, allowing for adjustments to the day’s training loads if necessary. To monitor the athletes’ hydration status, the same procedure used for heat stress is applied to urine samples, combined with a morning weigh-in. Athletes are monitored using questionnaires regarding their physical condition and even altitude sickness. Their blood glucose levels are also tracked using patches applied to the skin, which help determine whether athletes experience prolonged nocturnal hypoglycemia, which can cause fatigue during the training camp. This allows for adjustments to their diet by changing the composition of the carbohydrates consumed during their last meal.
Key Points on Adaptation and Outlook
Ultimately, the question of how to balance training intensity with the level of environmental stress is key to the success of training camps. Each athlete’s physiological response is taken into account to ensure that the body adapts properly without becoming overly fatigued.
Tailoring dosages is essential for elite athletes to maximize their performance.
Finally, the benefit of environmental stressors such as hypoxia and heat is that they elicit physiological responses that are beneficial for endurance performance (an increase in red blood cell count in the case of hypoxia, and increased cardiac contractility due to a rise in plasma volume in the case of heat). The idea of combining these two stressors to leverage the benefits of each is appealing. New research conducted by the CREPS in Montpellier is currently underway on this topic.
This article is published as part of the Fête de la Science (which takes place from October 6 to 16, 2023, in mainland France, and from November 10 to 27, 2023, in overseas territories and internationally), of which The Conversation France is a partner. This year’s edition focuses on the theme of “sports and science.” Find all the events in your region on the Fetedelascience.fr website.
Jonathan Rubio, Ph.D. candidate in exercise physiology, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.