Roland Garros has come to a close in Paris, with Alexander Zverev crowned the tournament champion, while the event also featured moments that underscored the toll extreme heat can take on high-performance sports. Jannik Sinner’s collapse during his match against Juan Manuel Cerúndolo on May 28 highlighted the risks of intense physical exertion in very hot conditions. With temperatures reaching nearly 33 °C and humidity running high on Philippe-Chatrier Court, a tennis court in Paris, France, weather played a major role in the athlete’s thermoregulatory strain.

Alejandro Lucía, MD, PhD, professor of exercise physiology at the European University of Madrid in Madrid, Spain, explained to El Médico Interactivo, part of the Medscape Professional network, what happens in the body during high-intensity exercise in extreme temperatures and why a collapse can occur. “In these highly stressful circumstances, the ambient heat is added to the large amount of metabolic heat already produced by the muscles,” said the expert. Thus, to prevent an excessive and, therefore, “dangerous” rise in body temperature, the body activates heat-dissipation mechanisms: sweating, followed by evaporation, and increased blood flow to the skin. However, when conditions are extremely demanding, such as high ambient temperatures, humidity, or prolonged exertion, these mechanisms may become insufficient.

As a result, the internal temperature can rise above safe levels — above 39 °C — a condition known as hyperthermia, which compromises both the central nervous system, which is highly sensitive to elevated body temperature, and the cardiovascular system, which loses plasma volume through sweating, reducing the heart’s pumping capacity. In extreme cases, this can lead to physical collapse or heatstroke, a potentially serious condition that requires immediate attention — that is, cooling the body as quickly as possible and then rehydrating.

Individual Factors and Heat Tolerance

Lucía stated that fitness level is one of the factors influencing an athlete’s ability to tolerate exertion in hot environments. Acclimatization is another key factor. Progressive exposure to heat improves sweating efficiency and cardiovascular stability.

Another key factor is pre-exercise hydration. According to Lucía, starting out well-hydrated is essential, and even more so if the body is acclimated to sweating more and sooner.

Genetics also influence sweating, heat tolerance, and cardiovascular efficiency. In addition, body composition must be considered. A higher percentage of body fat hinders heat dissipation.

Other factors to consider include age and sex, both of which can influence the body’s thermal response. In general, men tend to dissipate heat more effectively through sweating, which can be an advantage during exercise in extreme heat, while women are generally better at conserving fluids, a benefit that may support performance during longer workouts.

As for age, children generally have a lower capacity to sweat than adults, which increases the risk of overheating. In turn, older adults also have a reduced ability to lose heat not only through sweating but also through cutaneous vasodilation. This, combined with a poorer cardiovascular response and the fact that in many cases they take diuretics — which reduce plasma volume — means they are less able to dissipate heat than younger adults and are therefore at greater risk of heatstroke and dehydration.

Finally, underlying health status can also raise the risk. Certain diseases and medications make it harder for the body to cope with heat, particularly heart conditions such as heart failure; metabolic disorders including obesity, diabetes, and hyperthyroidism; and neurological, skin, and kidney diseases, as well as burns. Medications such as diuretics, beta-blockers (which are more commonly used with age and can reduce the heart’s pumping capacity), and antidepressants, because of their effects on the central nervous system, can also increase vulnerability. Alcohol adds to the risk as well by promoting dehydration.

Most Effective Strategies

Lucía reveals the strategies that can help prevent the effects of extreme heat: heat acclimatization, adequate hydration, and cooling strategies. Training in hot conditions for 1 or 2 weeks to help the body adapt — as is done in cycling, such as riding on a trainer with heaters and plenty of clothing, or going out on a bike ride wearing dark clothing, which absorbs more radiation; staying hydrated before, during, and after exercise, including electrolyte replacement; and cooling strategies, which we’ll see a lot of in the upcoming Tour de France.

Cooling strategies include pre-cooling measures and interventions during exercise. Among the former are the use of cooling vests, the consumption of cold beverages, or the application of crushed ice to areas with high blood flow, such as the back of the neck, with the goal of reducing body temperature before exposure to physical exertion. During exercise, these strategies rely on drinking cold water, applying ice, and seeking shade to limit the cumulative heat load.

During the recovery phase, staying in cool environments, along with the use of passive or active cooling strategies (including cooling vests), facilitates the return of body temperature to normal and reduces postexercise physiologic stress.

Other interventions include adjusting exercise intensity to reduce the workload under extreme conditions; wearing appropriate, lightweight, and breathable clothing that promotes sweat evaporation — preferably in light colors to minimize solar radiation absorption; planning exercise appropriately by avoiding midday hours and monitoringconditions such as temperature and humidity.

Finally, athlete education is key, with an emphasis on the early recognition of warning signs such as dizziness, disorientation, weakness, or decreased performance, which may indicate the onset of heat stress or imminent heatstroke.

This article was translated from El Médico Interactivo on Univadis, part of the Medscape Professional Network.