Heat, altitude: challenges and opportunities of environmental constraints for athletes
What will the temperature be like during the 2024 Olympic Games in Paris? With global warming, the number of sporting events taking place during summer heat waves is increasing. Athletes' exposure to heat is also increasing with the emergence of new nations hosting major competitions in hot regions, such as Qatar for the 2019 World Athletics Championships, the United Arab Emirates with the 2022 World Triathlon Championship Series final, and Senegal with the Youth Olympic Games in Dakar in 2026.
Jonathan Rubio, University of Montpellier
While specific protocols and regulations are beginning to emerge within various international federations allowing events to be canceled or modified in the event of extreme conditions (the most recent example being the Rugby World Cup match between France and New Zealand, for which cooling breaks were held between the two halves), athletes must also prepare specifically for the heat, otherwise they risk impaired performance in endurance disciplines, or even medical problems, including death from heatstroke in some cases.
When preparing for an important sporting event, endurance athletes such as triathletes usually spend several weeks training at altitude: since the 1968 Olympic Games in Mexico City, the benefits of altitude training have been scientifically documented. The main expected effect is improved performance through an increase in hemoglobin mass, allowing for better oxygen transport in the body and to the muscles, thereby contributing to energy production.
However, before competing in hot conditions, it is necessary to undertake specific preparation, involving staying in the same type of conditions, or at least training in them, which not only enables athletes to cope better with the heat, but also protects their health.
Environmental stressors in training can be beneficial... if used correctly.
Incorporating environmental stressors such as heat or altitude into training plans is not without consequences. When coaches plan training camps for athletes and add environmental stressors, these 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. Too much physiological stress causes fatigue, which prevents the body from adapting.
Today, to ensure that preparations for competitions run smoothly, athletes are closely monitored, with their condition recorded using various physiological parameters.
Training for competitions in hot conditions
When it comes to heat, athletes train in 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.
The desired heat stress is quantified, i.e., both the target temperature and humidity (generally around 38°C and 50% humidity). The recommended daily dose of heat is relatively low, around 60 to 90 minutes per day for daily training.
Athletes are equipped with capsules that they swallow several hours beforehand in order to monitor their body temperature in real time. This allows for better control of the risks of heatstroke and verification that the hyperthermia necessary for cellular adaptation is present (the goal is to reach 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, urine density to check that there is no excessive dehydration, electrolyte losses ([Na+], useful information particularly in the case of long-distance events, in order to compensate for losses with sodium-enriched supplements), hematocrit level (volume occupied by red blood cells in the blood), and exercise heart rate, the latter reflecting the overall state of acclimatization.
Perceptual markers 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 individualize protocols
The dosage of hypoxic training is much more complex and requires much more caution than heat training in order to achieve results, especially in endurance athletes who already have very high hemoglobin levels. While exposure time is limited in heat training, the aim is to spend much more time in hypoxia.
In the past, athletes were classified as "responders" or "non-responders" to hypoxic stress (i.e., some do not produce additional red blood cells after being exposed to a hypoxic environment), whereas we now know that an athlete who does not respond at a certain altitude and with a certain training program can become a responder by changing the dose of hypoxia, i.e., either by increasing the exposure time at the same altitude or by maintaining a similar exposure time but at a higher altitude. But things are not simple... because the dose must be increased for some and decreased for others.
This individual adaptation to hypoxic stress conditions optimizes erythropoietic responses (i.e., red blood cell production). It is with this in mind that endurance athletes today can sleep at higher altitudes than their place of residence, thanks to hypoxic chambers. Constant adjustments are made to the altitude regulation of the chambers in order to control the amount of daily hypoxic stress induced, thereby optimizing the athletes' fatigue levels.
The latter benefit from equally specific monitoring, notably with pulse oximeters that collect theirO2 saturation data during the night. When preparing for a competition that will take place immediately after the training camp, for example, 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 minimized. Overall fatigue is assessed each morning by analyzing heart rate variability, allowing the day's training loads to be adjusted if necessary. In order to check the athletes' hydration status, the same procedure as for heat is carried out on urine samples, combined with morning weigh-ins. The athletes are monitored using questionnaires on their fitness level and even altitude sickness. Their blood sugar levels are also monitored using patches stuck to the skin, which indicate whether the athletes are experiencing prolonged nocturnal hypoglycemia, which can cause fatigue during the training camp. This allows their diet to be adjusted by changing the composition of the sugars consumed during the last meal.
Key points of adaptation and outlook
Ultimately, the question of training intensity in relation to environmental stress is a key factor in the success of training camps. Each athlete's physiological response is taken into account to ensure that the body adapts well without becoming overly fatigued.
Individualized dosages are essential for elite athletes to maximize their performance benefits.
Finally, the advantage of environmental stressors such as hypoxia and heat is that they induce physiological responses that are beneficial for endurance performance (increased red blood cell count in the case of hypoxia and increased cardiac contraction due to an increase in plasma volume in the case of heat). The idea of combining these two stresses in order to combine their respective benefits is tempting. New research conducted by CREPS Montpellier is currently underway on this subject.
This article is published as part of the Fête de la science (Science Festival), which takes place from October 6 to 16, 2023 in mainland France and from November 10 to 27, 2023 in overseas territories and internationally, and of which The Conversation France is a partner. This new edition focuses on the theme of "sport and science." Find all the events in your region on the Fetedelascience.fr website.
Jonathan Rubio, PhD student in exercise physiology, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.