#480 The Science of Saunas: How Heat Boosts Fitness & Longevity - Brady Holmer MSc

Brady Holmer (0:00)

Dehydration is actually one of those signals that then forces your body to sort of upregulate all of those processes. When you become dehydrated, when you're sweating more, that forces your body to say, oh, we gotta uptick production of say EPO, and we gotta increase our plasma volume expansion. So if you're in the sauna and you're chugging a gallon of water and really not letting your body reach that dehydration point, like dehydration is kind of the point of the sauna sometimes. You don't get like a plateau where, oh, I'm not benefiting from the sauna anymore because I've been doing 30 minutes three times a week for years. You're still going to keep getting those benefits. Unlike exercise where at a certain point, you're going to kind of plateau in your benefits. You need to add more exercise. I don't really think that that happens the same way with the sauna.

Siim Land (0:40)

Brady, welcome back to the show.

Brady Holmer (0:42)

Siim, thanks for inviting me back on. Happy to chat.

Siim Land (0:45)

Yeah, we did our first podcast about VO2 max and aerobic fitness like a year ago. And yeah, this time I wanted to bring you back so that we could talk about something very interesting, in my opinion, which both of us have written about on online and in our books, which is a heat acclimation. And how does it relate to cardiovascular fitness and how can we leverage that for better performance and health as well? So maybe you can start with giving an introduction to heat acclimation and what does it actually entail? Sure.

Brady Holmer (1:22)

So heat acclimation sometimes goes kind of by the other names like heat acclimatization, but all the things mean pretty much the same thing. So essentially, you're training your body to perform better in the heat, and there are several ways to do it, and then there are several adaptations that occur. So how to do it, it seems pretty obvious. I'm sure we'll talk about some of those strategies, but the typical strategy is to exercise in the heat. Endurance athletes use it a lot, not just endurance athletes, I'm sure other types of athletes use it too, but exercising in the heat, an environment that is hotter or as hot as, say, the environment that you're going to be performing in. It's a strategy because, say, if it's winter and you're going to be performing at the Tokyo Olympics next summer or something, or you're training in the spring, well, it's going to be really hot there, and if your body is not ready to handle it, obviously, the heat is a huge stress.

So, exercising in the heat, typically, you can also wear some layers with that or add extra humidity. Athletes will typically do that to prepare themselves to perform in hot conditions. And the classical adaptations that occur, several adaptations occur when you do these strategies. I'm sure we'll get into some of the strategies. But the first one is, and maybe paradoxically, some people, but you will sweat more and you will start to sweat earlier. That is one of the main adaptations to heat acclimation. So it's funny because a lot of the times, you will say, you know, if somebody's outside and it's maybe a little bit hot and they're sweating a lot, you might think, oh, that person's like out of shape. Why are they sweating? But really, the more heat acclimated you get, you're going to start sweating earlier and you're going to sweat more. And that makes a lot of sense from a physiological perspective, because what is the point of sweating? Well, we sweat and that sweat evaporates and it cools off the body. It helps us cool down. So, the earlier you can start sweating when you're exercising in the heat, and the more that you can sweat, the better that you will be able to perform, and you'll be better able to handle the heat and regulate your body temperature. So, earlier on, instead of sweating, more sweating, that's kind of one of the classic signs of heat acclimation. There's probably also something that goes on, and I'm not too aware, updated on this, but like with the sodium content of your sweat as well, because obviously, if you're sweating a lot and sweating out a lot of electrolytes, that's not a good thing. You want to replace those. So sweating is one of the key adaptations as well. Several things also happen though in the body, and this will relate to the cardiovascular performance stuff that we're going to, I'm sure, get into later, but your plasma volume expands. So you get more plasma volume, you're just, that expands as well. And your red blood cell volume also maybe expands a little bit in addition to that, which would, you know, higher hemoglobin, higher hematocrit, so higher percent of your blood becomes red blood cells. Very similar to something that occurs with altitude training, which is kind of neat. There's some really interesting data on that. So overall, those are kind of the two key adaptations. Your heart rate in the heat during exercise is going to be lower due to that expansion of plasma volume, and just the fact that you can better regulate your body temperature. So those are kind of the two key adaptations that occur. And when you say somebody's being acclimated to the heat, that's what happens to allow you to just handle the heat better at rest also. But key is during exercise as well.