Sports in the heat – “Ignoring warning signals during exercise can be dangerous” – knowledge


Sweat, sweat, sweat: Sport is healthy, but high temperatures can really take a toll on the body. When does it become dangerous? Answer from the sports medicine doctor.

Sport is healthy and in fact we should do it more often. According to the Sport Schweiz 2020 survey, one in four exercise too little.

But how do we train in high temperatures and sunshine without negative consequences for our health? Tips and tricks from sports physician and senior physician Johannes Scherr.

John Scherr

Specialist in internal medicine, sports and nutritional medicine

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Among other things, Johannes Scherr accompanied the German delegation to the Olympic Winter Games three times as team doctor. The chief physician heads the center for prevention and sports medicine at the Balgrist University Clinic in the canton of Zurich.

SRF Knowledge: What are the biggest mistakes people make when playing sports in the heat?

Johannes Scherr: If you do not adapt your training to such temperatures, you are definitely doing something wrong. When it’s over 30 degrees, you shouldn’t run a ten kilometer long route at the same speed as in spring when it’s 15 degrees.

Training intensity is often maintained, however, because one has the feeling that only those who train hard achieve the desired effect. It’s not true! I recommend using this rough rule of thumb as a guide: the warmer it is, the more moderate your exercise. In other words, to significantly reduce the intensity and duration.

Another common mistake is to keep going when you feel dizzy, nauseous, have a headache, or are breathing fast. These are clear warning signals from the body. Ignoring them can be dangerous.


Because it can lead to cell damage in the brain, coma or even death. If you do not know what day it is during training or are otherwise disoriented, you should immediately go to the shade and take a break there, cool your body with water and drink.

What happens to the body when it’s really hot

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With high temperatures and sunshine, our body has to work hard to maintain the temperature. In hot weather, body temperature can be regulated in this way:

  • Heat is released through sweat.
  • The body craves water and salt. You feel thirsty.
  • The kidneys produce less urine to conserve water.

But if you move outdoors for too long and intensively, and these mechanisms reach their limits, it has far-reaching consequences for your health.

Direct sunlight can lead not only to sunburn locally, but also to sunstroke on the head. The meninges or brain tissue becomes irritated.

In extreme cases, cells can become so damaged that short-term memory or orientation to place and time deteriorates.

In addition, sports in the heat also have an impact on overall processes: combustion no longer functions optimally, stress hormones are released. The heart can no longer pump blood properly through the body, and in the worst case heatstroke can occur.

At what temperature does it become dangerous to exercise?

There is no fixed value, it varies greatly from person to person. Acclimatization is a decisive factor. If someone has trained in hot Spain for weeks, even months, that person can handle high temperatures better than someone who grew up and trained in Norway. How fit you are also plays a role.

Basically, the better you are trained, the more you sweat. And has a different sweat composition. You lose a lot of fluid, which increases the cooling effect, but you sweat out less salt.

The risk of having too little sodium in the blood is therefore slightly lower than in less healthy people. They are more likely to experience symptoms such as nausea, confusion or headache.

Summer sports: the most important rules of thumb

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Adjust duration and intensity: Exercise less and don’t push yourself to the limit. The sports doctor advises against completing interval units. For example, sprint at full speed ten times for several minutes.

Choose the time of day consciously: Do not go for a walk in the burning sun at noon, better in the morning when it is even cooler. If you only have time at lunchtime, move the training inside.

If you have any warning symptoms, stop immediately: Stop exercising if you are extremely thirsty, tired, excessive sweating, dizziness and confusion, headache, nausea, unusually fast breathing or fast heart rate, or dark yellow urine.

If warning symptoms occur, move to the shade and cool the body, especially the head. Consume fluids with sodium.

A number of studies show that heat takes a particularly toll on older people and young children. Do you generally advise these risk groups not to exercise?

No, but you should be more careful again. I would recommend older people to go for a walk in the woods rather than run around town.

In older people, the vessels are less elastic, which is the key to dispersing heat. They often have a different sense of thirst and drink less. This makes the blood thicker. Veins and arteries can become clogged, which in the worst case can lead to stroke or heart attack.

And why are children less able to compensate for heat?

Children generate more metabolic heat and generally sweat less than adults. Therefore, they can emit less heat.

The ratio of body surface area to weight must be taken into account. The more skin surface area to weight I have, the better. Conversely, obese people are more susceptible to heat.

Nina-Lou Frey conducted the interview.

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