How to Train Effectively in the Summer Heat

Kovács Ferenc Soma, Hungarian national record holder in middle-distance running

Summer has arrived, and with it the heat has returned to the Northern Hemisphere. Across Europe, days with temperatures of 36–40°C are becoming increasingly common. For most endurance athletes, this creates a major challenge: how can you maintain—or even improve—your fitness for the summer and autumn racing season? Fortunately, with thoughtful planning and targeted preparation, this is entirely possible. This article explains how the body’s physiology changes in hot weather and how athletes can adapt to these extreme conditions.

First of all, it is completely normal for runners to feel less fit in extreme heat. After the ideal conditions of spring, the body essentially has to relearn how to perform in higher temperatures. This process is known as heat adaptation. During running, metabolic processes generate additional heat, which raises core body temperature. The body regulates this increase through two main mechanisms: it transports heat from the core to the skin through the circulatory system, and it cools itself through sweating, as the evaporation of sweat removes heat from the body. Our bodies constantly strive for homeostasis—a state in which heat production and heat loss remain in balance. During exercise in extreme heat, however, this balance is disrupted: body temperature begins to rise as soon as metabolic activity increases, while the thermoregulatory system struggles to keep up. The good news is that the thermoregulatory system can be trained to respond more quickly and efficiently. That is precisely what happens during heat acclimatization. As a general rule of thumb, around four to six hours of moderate-intensity exercise in the heat may already be enough to initiate meaningful heat adaptation.

Above all, the most important factor is adequate hydration, both in quantity and quality. Fluid intake helps the body dissipate excess heat and also supports the proper functioning of its thermoregulatory systems. It is equally important to replace lost electrolytes and mineral salts. An isotonic sports drink mix is one of the most practical solutions for this. Fortunately, in the 21st century it is now possible to monitor fluid, salt, and electrolyte losses during exercise. I previously wrote about this in more detail in an article on conscious hydration. If a runner can see in an app exactly how much of each substance they have lost during a workout, it becomes much easier to replace what their body actually needs. Dizziness, severe fatigue, or difficulty maintaining orientation can occur if you lose more than 4% of your body weight through sweating. In addition, severe fluid and/or electrolyte losses can lead to muscle cramps. This is why it is particularly important during the summer months to pay attention to magnesium and potassium intake, potentially including supplementation where appropriate. Both play an important role in normal muscle function.

Elite runners also like to expose their bodies to passive heat stress before travelling to hot climates for training camps or competitions. I previously covered heat training in detail in my article “Poor Man’s Altitude.” Sauna and steam rooms are both forms of passive heat exposure. The main difference between the two is humidity: while a sauna typically has around 10% relative humidity, a steam room can reach 95–100%. Both methods can enhance heat adaptation, but they produce somewhat different physiological responses. In a sauna, the high temperature triggers intense sweating, while the dry air facilitates sweat evaporation. In a steam room, by contrast, the high humidity inhibits sweat evaporation, meaning that the body experiences a greater thermal load at the same temperature. For this reason, beginners should generally start with shorter 10–15-minute sauna sessions, while steam-room use requires greater caution, particularly after high-intensity training. Passive heat exposure should always be performed in a well-hydrated state, and it is practical to incorporate it within 30–60 minutes after training. Research suggests that 2–4 sauna sessions per week, lasting 20–30 minutes each, can produce measurable improvements in heat tolerance within just a few weeks: resting and exercise heart rate may decrease, plasma volume can increase, sweating may begin earlier, and the electrolyte composition of sweat can become more favourable. These adaptations are beneficial not only during hot-weather running but may also contribute to improved endurance performance in more moderate conditions.

During summer training, however, it is important to consider not only the heat itself but also when you train. Whenever possible, avoid long runs or high-intensity sessions during the hottest part of the day, roughly between 11 a.m. and 5 p.m. Temperatures are generally lower in the early morning or late evening, placing less physiological stress on the body. If you have no choice but to train during the day, reduce your pace and regulate intensity primarily by heart rate or power rather than trying to maintain your usual kilometre pace. In the heat, the same running pace can impose a substantially greater physiological load.

Finally, it is important to remember that heat is not an enemy. It is an environmental stressor to which the body can adapt. Gradual heat acclimatization, adequate hydration, electrolyte replacement, and intelligent training planning can work together to ensure that the summer months do not set back your progress, but instead lay the foundation for a successful autumn racing season. If you patiently complete the adaptation process, after a few weeks the same temperature will place considerably less stress on your body, and you will once again be able to perform at your best.