"You drink pure water? That's nonsense," says the doctor

• In the video: Better than water: These three drinks should be drunk in summer

With the current hot summer temperatures , outdoor pools, lakes, and beaches are packed ; however, the gym is completely empty. Joggers are also increasingly leaving their running shoes in the closet – perhaps because they fear circulatory collapse in the heat.

Sport is certainly possible at temperatures around 30 degrees, says Wilhelm Bloch, professor at the German Sport University in Cologne, in an interview with " Stern ".

After all, the body can adapt to the warm weather within a few days and adjust sweat production, which then cools the body down. "However, this only applies to middle age; in children and the elderly, thermoregulation usually takes longer, so you shouldn't put too much strain on them in the heat," says Bloch.

But you shouldn't overdo your training. "Give your body a few days to adjust to the heat. And don't forget to drink."

To ensure adequate hydration, the professor recommends drinking plenty of fluids before training. "Because it becomes difficult to replenish lost fluids during exercise." Relying solely on your own thirst, however, is not a good idea. "Those who rely on their thirst when training on hot days are drinking too late," warns Bloch.

The choice of thirst quencher also requires careful consideration. "You drink pure water? That's nonsense," the professor told Stern magazine. "I recommend an isotonic mixture, which has roughly the same number of electrolytes as your blood, plus around 50 to 90 grams of carbohydrates per liter."

An alternative is to mix two parts water with one part fruit juice and add a pinch of table salt. "With pure tap water, however, you risk hyponatremia, a salt deficiency in the blood, which can lead to nausea, headaches, and vomiting," says the professor.

Bloch also advises endurance athletes, in particular, to consume carbohydrates before running. These not only provide energy to the muscles—they also bind water, acting as a kind of water reservoir.

"For example, I like to eat Chinese fried noodles before a long-distance run. The next morning, I easily weigh three kilograms more than usual, which is an advantage," says Bloch. His tip: "Go into the race heavy! Most of it is water, which is then released when the carbohydrates are burned."