Interviewer: So the question is, can you build up a tolerance to heat exhaustion or even getting heat stroke as the summer progresses.
We're with Dr. Scott Youngquist. He's an emergency room doctor at University of Utah Health Care. So the question is, can you build up that tolerance or is it just always the same.
Dr. Youngquist: The short answer, Scot, is yes, you can build up tolerance to heat exposure, and this has been shown for some time now, experimentally, with human volunteer subjects, that you can take them and, typically, under conditions of exercise. So you put one group into an area where they're going to exercise under heat conditions, around 37 degrees Celsius or 98.6 degrees Fahrenheit. You have them exercise for 20 minutes and then have a 10-minute cool-down period, and you do this for 6 days, and they will tolerate passive heat exposure much better than somebody who exercises in the cold. So you can develop this.
When you're exposed to heat, a couple of things happen to try to cool your body and adjust to the heat stress. One of those is, you start to hyperventilate and that will reduce blood flow to your brain. So you start to lose the amount of blood going to your brain. That's why people can get altered mental status with heat stroke. We call it heat stroke, not because they're actually having a stroke, but because, sort of like a stroke, their brain is deprived of essential nutrients and oxygen. So that occurs.
You also have a diversion of blood flow toward the skin, so you sweat and also your skin heats up so you can radiate heat from the body and try to lose heat that way. But that also reduces your circulating blood volume and so you get a drop in your blood pressure, and that can be, in cases of severe heat stroke, that drop in blood pressure can lead to cardiovascular collapse.
And so you have a couple of compensatory mechanisms when you're exposed to heat, and at a cellular level, there are these proteins called heat shock proteins. The heat shock proteins are produced in response to this, and give you this tolerance. So people who are exposed to exercise under conditions of heat build up this tolerance by producing these heat shock proteins. And what you find is that they hyperventilate less, there's increased blood flow to the brain compared to the group that hasn't developed tolerance, and so they're able to compensate much better. They also increase their plasma volume, so they hold onto water a little bit more, anticipating they're going to be sweating and things like that.
Interviewer: So at the beginning of the summer when I feel like, "Oh man, I'm just having a hard time handling the heat," versus the end of the summer, where I'm running and cycling, and it doesn't bother me at all, all those things are happening inside my body.
Dr. Youngquist: Exactly. That's why you feel better as the summer goes along in the same amount of heat.
Interviewer: And I would imagine that everybody's a little bit different. Some people probably have a natural higher tolerance, right?
Dr. Youngquist: Yeah, absolutely. So if you are obese or overweight, it's going to make it harder for you to develop heat tolerance because you've got that extra layer of insulation.
Interviewer: If I'm interested in building up heat tolerance because I want to compete in some sort of an athletic event, is there a systematic way I should go about it, or is it just about getting out for longer and longer periods of time?
Dr. Youngquist: There are several protocols you can look at online. So if you do a Google search, you'll find several proposed heat tolerance regimens that you can adopt. But experimentally it's usually just a small amount of exercise, about 20 minutes a day for 6 days straight, in the heat, being careful to hydrate yourself well and to stop if you're feeling dizzy or excessively tired, and that should do it.
Interviewer: All right. Well, thank you very much. Indeed, you can build up a tolerance to heat exhaustion.
updated: July 16, 2021
originally published: August 6, 2015
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