know the risks of high temperatures

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practice exercises hot yoga or cryotherapy, subjecting the body to extreme heat or cold, can bring harm to health. Even the risk is even greater for people who have cardiovascular problems.

On a March morning, when the thermometers marked 3°C in Aarhus, Denmark, the city’s pier was crowded. During this time of year, the sea temperature in the region does not usually exceed 2°C.

Before swimming, most visitors spend a few minutes at around 60°C in the seaside public sauna – it was packed on a sunny Sunday. Then they take a few steps out onto the deck and into the icy ocean water.

It sounds crazy, but diving into the cold sea after a sauna session, as many Danes do every week, is a habit that is becoming increasingly popular in other countries too. Other practices that involve changes in temperature, such as hot yoga, in which postures are practiced in rooms heated to up to 38°C, or cryotherapy sessions, a technique that uses cold water to relieve symptoms of sports injuries, are also becoming popular in the United States. last years.

Despite this, experts warn that subjecting the body to extreme temperatures can bring serious risks. According to cardiologist Luciana Janot, from Hospital Israelita Albert Einstein, swimming in the icy sea, as many residents of Scandinavian countries do, can be risky for those with cardiovascular problems.

Risks and benefits of thermal practices

“This scare of cold water will cause an immediate constriction of the vessels, because we try to make the body lose less heat, so there is a narrowing of the vessels and an increase in blood pressure. At this time, an arrhythmia may occur, because there is stress for the heart. For those who already have a previous cardiovascular problem, this is not indicated at all”, explains Janot.

Doctor Mike Tipton, professor at the University of Portsmouth, in England, is one of the main researchers of the effects of immersion in cold water, or Cold Water Immersion (CWI), as ice diving became known in English.

For the specialist, although the practice has many supporters, there is still no scientific evidence that the low temperature is responsible for the supposed health benefits attributed to “cold plunge” (cold dip).

“We still need to have a definitive and controlled scientific experiment done properly, that is, an experiment that isolates the cold water factor from the other aspects involved in practice”, explains Tipton.

“Most people who are going to practice cold water diving go to a beautiful place to do it, they go with friends. So, they have socialization, they have visual stimuli, they exercise. Therefore, cold water is only one aspect”, says the expert.

“What we need are studies that say, okay, is it the cold? Is it the fact that you’re floating on water? Is it physical activity? Is it socialization? Is it the feeling of accomplishment for having survived an extreme experience?”, asks the professor.

Scientific evidence do Yoga

Although the benefits of cold diving in the sea have not been proven, the use of cold to treat specific problems already has solid scientific evidence. This is the case of using ice for sports injuries, for example. This principle is what lies behind a technique called cryotherapy, in which parts of the body are subjected to very low temperatures to reduce tissue inflammation.

“In the case of cryotherapy, it was created because we know that the use of local ice in small amounts has analgesic power, that is, it relieves pain, and is anti-inflammatory”, explains sports doctor Karina Hatano, from Hospital Israelite Albert Einstein.

“Among the sports recovery protocols, the one we have the most support for is the use of ice, for up to 20 minutes, in the area that was trained”, he adds.

However, there is still a lack of scientific evidence to justify the use of ice in other contexts, in addition to topical use for 20 minutes, and to support the use of contrasting temperatures in the recovery of athletes, according to the doctor.

Check-up before starting the practice

Although they do not bring risks to most people, when practiced occasionally, these activities can be dangerous for some individuals. So it’s important to check if your health is up to date before joining them.

“What is most delicate about these strategies that are in fashion is that they carry a series of risks. It is always important to have medical advice and a checkup before adopting more intense physical activities or recovery strategies. You have to be careful with these fashionable practices”, evaluates Hatano.

In addition to a prior assessment, experts also recommend gradually adapting to extreme temperatures. In the case of sauna or hot yoga, for example, the ideal is to start with short periods and reinforce hydration before and after practice.

“When you practice hot yoga, for example, there is a great risk of dehydration, and this can even lead to fainting, for example. In extreme cold, such as in an ice bath or a dip in cold water, there is a risk of hypothermia and vasoconstriction”, explains Hatano.

Cardiologist Luciana Janot also points out that practices in very hot environments bring two combined risks: intense exercise and extreme temperature.

“In a hot and humid environment, like hot yoga, we have vasodilation, and this causes us to have an increase in heart rate and a drop in blood pressure. Who is already hypotensive [tem pressão baixa], or sensitive to heat, in such an environment there will be a great chance of feeling sick. Is everyone sick? No. Are there people who get used to it? Yes, but you have to be careful”, explains Janot.

In addition to staying hydrated, another important precaution when exercising in high temperature environments is to reduce the intensity of the activity to avoid injury.

“The heat can give a feeling of release, of analgesia, and we have more relaxed muscles. This way, we can do longer stretches, for example, and it is easier to pass the point”, says the cardiologist.

In the case of ice baths or cold water dips, it is essential to have an up-to-date medical check-up before venturing out on your own. Still, it’s important to remember that many more subtle cardiovascular problems can be missed in routine tests.

“Even with health up to date, we know that it is not for everyone. For those who have never ventured out, the time in the water has to be shorter. It will also depend a lot on the prior tolerance to the cold of each one: if it is a person who normally has difficulties, I think it might not be pleasant”, evaluates the cardiologist.

For diving in cold water, the ideal is to start with intermediate temperatures and gradually increase the bathing time, never exceeding the 10-minute mark.

“There is no reason to stay longer than 10 minutes [na água gelada]. The benefits won’t be greater if you stay longer, and there’s no point in basing it on how you feel, because after a while the body gets used to the cold water, but the body continues to cool down at the same rate, which can be dangerous,” explains Tipton.

It is also necessary to be extra careful with the temperature contrast, that is, with exposure to cold right after heat, or vice versa. This is what happens to people who practice ice diving right after leaving the sauna, for example.

“For healthy individuals, taking a sauna before the cold plunge probably reduces the cold stimulus in the initial immersion, so it becomes easier to get into the cold water. However, if you suffer from cardiovascular disease, the sauna can be dangerous in itself, and so can immersion in cold water,” says Tipton.

“If you combine the two practices, you are doubling your chances of having a problem”, completes the doctor.

Others health benefits

Studies linking extreme temperatures and health benefits are often based on positive reports from people who already practice these activities. Therefore, it is still difficult to assess the effect of these temperatures in unbiased research, explains Professor Mike Tipton of the University of Portsmouth.

“There are many studies where researchers ask people who swim in cold water, ‘Do you think it’s good for you? And how do you think it’s good for you?’ And of course they say yes, because it would be really dumb to do something that you don’t think is good for you,” says Tipton.

“If you ask a runner, ‘Do you think running is good for you?’ The chance of him saying no is very small”, exemplifies the researcher.

Even if they don’t have proven benefits, practices that involve extreme temperatures, such as hot yoga or diving in cold water, are gaining followers around the world because they bring an immediate feeling of well-being. In addition, another factor that may explain the popularity of these activities is the stimulus of experiencing temperatures with which the human body is no longer used.

“Unconsciously, people have noticed that they have become very static not only in terms of physical activity, but also in temperatures. Environments these days are so controlled that we almost never feel too cold or too hot, and that’s not good for us. People want a new stimulus in this regard”, assesses Tipton.

According to the main studies on the subject, the benefits that practitioners of these activities most report are related to stress reduction and a generalized sense of well-being.

“One of the advantages that practitioners report is feeling more awake, more alive, and that feeling lasts after the activity. This is common because cold temperatures cause the body to go into an urgency mode and release adrenaline,” reports Tipton.

Technical review: Alexandre R. Marra, researcher at the Instituto Israelita de Ensino e Pesquisa Albert Einstein (IIEP) and permanent professor at the Graduate Program in Health Sciences at the Faculdade Israelita de Ciências da Saúde Albert Einstein (FICSAE).


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