2023-08-04 12:11:21
Sweat, redness, fatigue: heat has multiple effects on our body. But why do these effects vary from one individual to another? Can we even get used to more and more frequent heat waves? The duty asked a specialist regarding it, who isolated several factors that can influence our ability to withstand high temperatures more or less well.
When exposed to heat, our body produces sweat — allowing it to cool as it evaporates. The heart also starts beating faster, which brings more blood to the skin’s surface — hence the redness it can cause. Both of these responses are automatic mechanisms, called “physiological responses”.
“Our physiological responses depend on the amount of heat we produce and the amount of heat we potentially gain from the environment,” explains Daniel Gagnon. This physiologist at the University of Montreal is a specialist in the effects of heat on the body. He is also the co-author of a literature review on the subject published in 2022 in the journal American Physiological Society.
A question of morphology
This amount of heat generated by the body varies in particular according to morphology, he specifies. The researcher takes the example of two people walking on a treadmill, one weighing 50 kg and the other 100 kg. This exercise will require the second person to carry a more substantial mass, therefore will require greater energy, which will cause him to generate more heat.
Depending on the physical form of a person, the heat thus produced can then be evacuated more or less well by the body. “If we train, we will be able to do exercise intensities that are higher and higher, so we will produce more heat,” points out Daniel Gagnon. The researcher adds, however, that an athlete is able to evacuate heat from the body better; therefore, although it will produce more heat, it will not necessarily be hotter.
Other factors to consider
In addition to these differences, there are also variations according to age or biological sex, for example. The researcher explains in particular that because of its very small size, internal temperature changes in a baby occur much more quickly than in an adult. “Before the age of two, infants aren’t going to really sweat, so they’re not able to expel as much heat as we are,” he says. Same thing for seniors: “As we age, we produce less sweat, so we are less able to evacuate it,” he says.
The two mechanisms of sweating and increased heart rate that cool the body also have different impacts on individuals, depending on their heart and kidney health. “If the heart is not able to support this additional work, it can predispose to a heart attack”, warns Daniel Gagnon. The same goes for the kidneys: people who have kidney disease might find themselves dehydrated. In fact, “electrolyte imbalances and kidney failure are the number one cause of hospitalizations during hot weather,” he says.
A physiological response that varies
The researcher points out, however, that two people of the same age, the same sex and whose morphology is similar can also sweat or struggle more or less when faced with the same exercise.
These variations may be due to the way our receptors perceive the ambient heat, to the way our brain interprets this information. It can also be at the level of blood vessels or glands that produce sweat. “It’s a bit of a mix of all that so that the answer can vary,” sums up Daniel Gagnon.
Different feelings
In addition to the physical differences between individuals, the researcher also points out that two people do not always tolerate heat in the same way. “You can have the same physiological stimulus, but two people will perceive it completely opposite,” he says. We see it in the laboratory, when we invite people to come and expose themselves to heat. Some love it, some hate it. We don’t really know the exact reason for this. »
Athletes, in particular, have a greater tolerance for high internal temperatures. “They are able to tolerate internal body temperatures of 39, 40°C, which for us would be intolerable — that’s close to heatstroke. But these very high level athletes are probably able to suppress the cues that tell them “I’m hot, I have to stop”, because they’re so motivated that they’re going to be able to push themselves through it. for their performance,” he said.
A possible adaptation?
Our reactions and our tolerance to heat are therefore highly variable from one individual to another. The good news, however, is that this tolerance is not set in stone. “If you’re exposed to heat on a regular basis, you become able to adapt, and probably tolerate it better. That has been fully demonstrated,” says the researcher.
In a context of climate change, Daniel Gagnon is therefore optimistic. “We will probably have to change our behavior, our lifestyle. But the good news is that we are able to adapt and tolerate the heat a little bit more,” he points out.
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