Exercise Physiology | Temperature Regulation during Exercise (Part 11)
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Welcome everybody to another episode of Dr. Matt and Dr. Mike's medical podcast. I'm your host, Dr. Mike Todorovic, and I'm joined today by my co-host, straight off the set of Fantastic Four, and the last of us, Pedro Pascal. I love you, Pedro. Nice mustache. When I was doing my cycle trip through Canada in the Rockies, I remember I was at this remote cafe and

And a grizzly bear came in and ordered a coffee, said, can I have please a short macchiato? The barista said, yes, but why the long pause? I was born that way. Wow. That's terrible. That's terrible. Get it? Yeah. Yeah. No, don't get me wrong. It's, I didn't laugh not because I didn't get it. Yeah.

How are you, Matt? You good? Not too bad. What's happening? What's new? Not a great deal. I went to a carrot farm on the weekend. Oh.

Just so everyone knows, the reason why I'm laughing here is because I asked Matt, hey, what did you get up to on the weekend? He goes, oh, it was great. Took my kids to a carrot farm. And I'm thinking, wow, dad of the year. These kids, imagine the memories these kids are going to have. It was actually quite interesting. We got to pick them. We got to see how they get processed through a factory, how AI selects the different types of carrots, the disfigured carrots. Your poor kids. Your poor kids. Wow. They're going to be farmers. Yeah.

They're going to be bullied. Um, well, look, I didn't go to a, I didn't go to, and then I invited you to go with your kids to go to an adventure playground. And you denied me. It would have been weird if you invited me and said, don't bring the kids. Mark, I'm going to an adventure playground. Leave the kids at home. We're going to have a blast. Um, well, I didn't do that. What did I do on the weekend? Uh,

I was raining most of the weekend. I wanted to do yard work. I've got all these stupid trees to cut down, which I think everyone's- I thought I'd cut- You need to come back because you haven't- Matt cut a whole bunch of trees. Matt's chainsaw, of course, he'll make a joke here, is bigger than my chainsaw and had to cut a couple of big fir trees down and a couple of yuckers down. But-

Stupid Matt didn't cut low enough down the trunk. So the stumps that I have left are too high for me to get a stump grinder in. And so, yeah, it's – I need your back. Or give me the chainsaw so I can do it. Or you could contact Kramer. He knows how to get rid of stumps. Does he? Yeah, muffin stumps. Haven't you watched the episode? I don't think they're called muffin stumps.

I don't think that's how they were referred to. Yeah, it was. As top of the muffin to you, but they didn't call them the stump. Because remember he said, and it's probably a very, you say, inappropriate joke now. He said something because he had a bus and he was getting rid of them that way. So he was picking them up in bags from Elaine. Elaine? Elaine. And then something like his...

saying something about the stumps, trying to get rid of the stumps. And then he said something about veterans. Oh, I don't actually remember that, but that was a good, but that's the top of the muffin to you episode. Very funny. Just selling the muffin top, but obviously they had to pull the muffin bottom off. All right, Matt, let's jump into this. We're talking about temperature regulation.

This is important for us to discuss because obviously cellular structures, metabolic pathways, they're all affected by temperature. If our body temperature goes up too much, it disrupts enzymes. If it goes too low, it disrupts enzymes and enzymes do all the functional things within the body so we don't want that to happen. Now, we've spoken to great extent about homeostasis, maintaining a happy, healthy balance physiologically.

Here, as human beings, we are referred to as homeotherms. Did you know that? Makes sense. Makes sense. So we maintain a core body temperature. And what we're trying to do is maintain heat loss with heat production. We want to get rid of the heat that we're producing to the point that we maintain our internal or core body temperature, which is what in Celsius? Nice that you bring that up.

As in the Celsius part. Oh, okay. Opposed to Fahrenheit. Or you could be Kelvin. We could be Kelvin. I'll be Kelvin, you be Frank. So what is it in Celsius, internal body temperature? 37. Do you know what it is in Fahrenheit? I don't. Almost 100. Oh, okay. Do you want me to give you the scales quickly, how they're devised?

What do you mean? How we made Celsius? I'm not going to give you the person's names. Yeah, okay. Yeah, no, go for it. Andres? You just said you weren't going to give us their names. I'm guessing that. He was Swedish. Why would you guess a name? It started with A, definitely. Andres or Andrea, something like that. Celsius. So he was Swedish, but he was a mathematician slash astronomer.

And interestingly, I think this is correct. So you don't know his name because he made it up. And now you're going to tell us a fact which you probably made up. Please correct me, listeners, if this factoid is incorrect, but I'm confident it's okay. So when he devised the Celsius scale, it was actually in reverse. So...

boiling of water, boiling point of water was zero and the freezing point was 100 because he was more focused on the freezing of water, not so much of the other properties because as a mathematician astronomer, he understood that more...

the properties of water became more stable as it become more and more frozen. And as you approach absolute zero, there's no more molecular movement. So he was more focused at the freezing end and he wanted to kind of refine that point. So he made freezing at a hundred degrees. Yeah. But then it was reversed after his death. Well, my thought would be, because if you made freezing a hundred degrees and then you made boiling at zero degrees, what then happens at below zero degrees?

You mean like above 100? Like 200, 300, 400? Well, yeah. If you're saying that boiling happens at zero degrees, then what happens to water at negative one degree? Negative 10? Just hotter? I don't know. Just the properties of the water molecules change. So he flipped it? He didn't flip it. Okay. They did after his passing. And what about Fahrenheit? Fahrenheit also around water. I guess both of them around water. What's their name? I'm not going to even attempt. Okay.

Can we say Frankie Fahrenheit? I think he was Polish. Okay. But also check that. So he... Check that. Zero Fahrenheit was the point at which water would freeze with a lot of salt in it. So salt, sodium chloride plus, I think, also ammonia, all right, or if that's possible. So...

A slushy kind of salty mixture. And when that froze, that was zero Fahrenheit. But when pure water freezes, it's 32. And then ballpark, human body's about 100 degrees, but probably more like 98.6 degrees Fahrenheit. Okay. Physiologically. And then I think the boiling point of Fahrenheit, 212. All right.

Well, look, I'm very glad we took that turn. Let's get back. I thought that was interesting. No, it is interesting. You know what I'm like. I just like hanging crap onto you because it's just easy. It hangs well. So what was your question? I didn't ask one. No, you did it starting the night. Oh, I said what's the core body temperature? Yeah, so 30...

No, 36.6 to 37.2. Let's just say 37 degrees Celsius. Great. Or 98.6 Fahrenheit. So a five-second answer into a 10-minute aside. A history of how temperature scales were created. At least you can bring up how dogs are incorporated into the process. So we have to maintain our internal... Dogs are homeothomes. Yeah.

Yes, that's true. Meaning they need to maintain a core body temperature and they need to match their heat loss with their heat production. Now, interestingly, Matt, what we're going to talk about today is the principles of temperature regulation during exercise. So we...

we'll talk about how temperature is or heat is produced in the body at rest, but we're also going to talk about it during exercise and then how we maintain internal core body temperature, but also how we remove that excess heat. And then a little bit about what happens when we train in the heat and train in the cold. All right. But importantly, which I think is an interesting way to look at it, our body is more like a furnace system.

Okay. Our body functions more like a furnace than it does like a refrigerator. So I'm not just talking about it's hot as opposed to cold. I'm saying that the body is- Controls heat. Yeah, it's better at- Controls temperature. Producing and then releasing the heat as to producing cold and maintaining warmth. It's like you've got a fireplace on and you're just throwing logs into it to increase the heat, but at the same time you're just-

allowing heat to dissipate by opening windows and so forth. Yes. Opposed to... Not trying to produce the heat and just maintain what we've got. Or you get in too hot and then you actively have to put the air conditioner on to cool the house down. Yes. It's easier to lose heat than it is to maintain body temperature. Okay. If that makes sense. So first question I want to ask you, Matt, is where does heat come from?

The sun. Okay, let me be more specific, smartass. Where does body heat come from? I guess you'd just say metabolic processes in the body. Yep, that's true. Through the generation of energy. Yeah, yeah. Generation and liberation. Yeah. ATP. Well, yeah, if we think about metabolic processes, like turning macronutrients into energy, it's not –

No. 20 to 30%. So things like a diesel engine. Right. About the same percentage of efficiency. Oh, okay. So 20 to 30% of macronutrients undergo metabolism. It's efficiency from... So if we take carbohydrates, for example, and we want to turn it into ATP...

Only 20% to 30% is efficient at doing that. The rest just produces heat. So we're very good at producing heat as a byproduct of metabolism. And then when you add on top of that of doing exercise, so your muscles are now actually generating work.

that process generates even more heat. And so now you go into an area of overheating. And so that's the muscles contracting and relaxing, utilizing ATP in that process. And again, heat is generated as a byproduct of energy. Correct. So during exercise, then we produce huge amounts of heat.

That's right. And so therefore we need a good system to be able to dissipate it, get rid of it. Cool. Okay. Now I think if we have a quick look at heat balance during exercise. So during exercise, our body temperature is regulated by making adjustments, right? In the amount of heat lost. That's effectively what we're doing, right? So we want to increase...

the heat coming to our skin to release it if we want to reduce our body temperature. But if our body temperature goes too high and we're too – so if our body temperature goes too high, we want the heat to get as close to our skin as possible to release it. And if our body temperature goes too low, we want to move it away from our skin. But how do we get it to the skin? That's the question. Yeah.

Right. So this would be kind of the idea that the body has a core and a shell and there's a gradient between the core and the shell. So it's like a Ferrero show. Yeah. Okay. We can go with that. Okay. So...

The core being the gooey Nutella on the inside. Yeah, that's where all your organs are. Yep. So we'll just call it your central system or your core. That's fine. And then the outer part, which is your skin, that's the shell. That's the vortex of your volume. And we have to kind of create a heat gradient between the core and the skin. So they're not the same temperature? No. Okay.

Okay. So what's the core temperature? That's that 37 degrees Celsius. So that has to be pretty stable. And there's good systems in place to maintain this. We have a good central thermostat, which is your hypothalamus. And that keeps it in close regulation. So there is two kind of temperature sensors that are located on your body or in your body. There are the...

The Michael's drinking from a water bottle and sounds like he's playing a drum at the same time. I don't know if we're doing this on the top of a mountain or where, I don't know, but the bottle keeps crunching and popping. Apologies if you're hearing that. So the thermoreceptors are going to be located on your shell, so your skin, but you also got probably more finely tuned ones in the

which is your spinal cord and the hypothalamus as well. Right, okay. And so they are giving you a very precise temperature readout to know exactly what the temperature is. But at the same time, if you go out into a cold or hot environment, ambient environment, you will perceive there's a temperature change. So your skin will pick that up. And so that will relay back to your brain to say, oh, this is a change. Beware or be mindful of it.

But it's probably more the core thermoreceptors that are going to be more profound in the way it changes physiological process to try to get rid of heat or retain heat.

So the core 37 degrees, what is the shell? What's the temperature of our skin? Well, that can change. So that can change depending on the outside environment. But the gradient, you'd need to really, particularly in the exercise side of things, and exercise physiologists and those who are working with athletes really need to ensure if they're trying to regulate temperature,

heat loss, so this is probably more of a concern than heat retention, they need to ensure that the gradient between the core and the skin is maintained because they have to keep dissipating the heat to get rid of it to regulate your temperature. Because as you said, if you're not regulating your temperature well and you are gaining heat,

your performance is going to start dropping. So generally speaking, the skin tends to be four degrees lower than the body temperature. But if you're in a really cold environment, it could be 20 degrees lower, right? Yeah. And effectively, this heat that's generated through metabolism is handed over to the blood and it's circulated through the bloodstream. So the circulatory system is the way that we sort of distribute the heat. Yeah, and that would be a form of convection resistance.

which is a process where the temperature, in this case heat, is being handed off to other things that have been moved away. So convection can be both in air but also in liquid. And as we see when we look at the way that the body employs certain processes to get rid of heat, convection is one. And one that's a lot more efficient is air.

opposed to air. So this will probably be more profound when we look at cold environment than heat. But if you were in the water, you would be able to, and it was cooler water, you would be able to control your body heat loss much better than if it was just air. It's like 25 times more, the word...

at taking heat away or temperature away? All right. Well, before we jump into the way we remove heat, let's just talk about how we produce it. So we spoke about producing it through metabolism, but we know that that's not the only way that we produce heat. So if our... So under normal...

Conditions, room temperature, normal physiological conditions where internal body temperature is 37 degrees, yes, metabolism is going to be producing that heat. But as we know, we can produce heat a couple of different ways. So we've got voluntary ways to produce heat, so that's exercise, and involuntary ways to produce heat, which includes shivering.

So when it gets too cold, our muscles will contract, relax, contract, relax, producing heat as a byproduct. But we've also got biochemical ways to produce heat. So this is feeding into what you were saying about the metabolism because –

In a way, we need metabolism to happen all the time. It's like an idling car, right? The car needs to just idle in order to maintain our body temperature. And that is controlled quite profoundly by thyroid hormone, but also the catecholamines, basically noradrenaline or norepinephrine. So these hormones can tweak it?

Yeah, they're sort of ensuring that the – so the way I think about it is that thyroid hormone is keeping the engine idling so that you can metabolically pivot when needed and maintain body temperature. But then if you really need to pump body temperature up, you can pump out some catecholamines, some noradrenaline, and that's sort of like revving the car, right? Excessively probably, right? Excessively. Because you know how sometimes when you're in the car and then you turn on some things like air conditioner, then you'll see the idling go up? Yep.

But then I guess if you really want to drive the car, then you need...

More power. Yeah. So the thyroid hormone is sort of letting the car idle. It produces heat as a byproduct, maintaining core body temperature. But then if you really need to pump things up, you pump out some noradrenaline and that's going to put the foot on the accelerator while you're in neutral and it's revving that car up. And probably added to that, you also have thermogenesis through brown fat. That's true, yes. So explain a bit more about that. Well, this is just...

Fat, as we generally understand it to be as a tissue, is a storage site for calories, which you can use when you need to draw upon more energy. Now, that's usually referred to as white fat, right? But then there's another type of fat called brown fat, and that is seemed to be more prevalent in kids, right?

like infants and they utilize that to maintain their body temperature heat when they're

But we also have brown fat. We do have brown fat. And we probably realize we've got mixtures, more mixtures than just yellow, brown, and then there's in between. Now, infants utilize this process because I don't think they've fully developed their shivering process overly well. So they do rely on this a bit more. But this goes back to the electron transport chain, if you remember. That's right, yeah. And it's just the carrying of electrons through. And I think it's one of the proteins that...

In brown fat, it just decouples it. And instead of passing the energy through, it just generates more and more heat. It's

So instead of producing all that ATP at the end, it just generates more heat. And certain animals do this quite efficiently in hibernation. And that's how they keep their temperature stable over long periods. That's uncoupling. Yeah. So the process of uncoupling. So thyroid hormone uncouples, right? So thyroid hormone plays a role in brown fat and uncouples the electron transport chain. And like you said, it means that effective transfer of electrons and proton pumps don't

don't result in ATP. It just results in heat. So effectively you're wasting energy. That probably explains particularly with, you know, like primary school boys, right, where you see them in the middle of winter running around with T-shirts and shorts. They never get cold. Yeah. They have a lot more higher actin.

thyroid hormones and therefore their metabolism and they are hotter. Yeah. Yeah. Yeah. All right. So we're producing heat. We've got this voluntary, which is exercise, heat production, but involuntary, which is shivering. And then you've got what's called non-shivering thermogenesis and that's the thyroid hormone and the catecholamines. So now we're producing this heat, right? Now, if we think about producing the heat again through exercise, shivering or, you know, non-shivering thermogenesis, we're

We will hold on to as much as we need to maintain 37 degrees and then we need to lose it. We need to lose the excess amount. So then the question is how do we lose this heat? And there's a number of different ways. So you mentioned one before, which was convection, right? I think probably the best one is radiation.

Well, let's just name the four different ways and then we'll go into detail. So it's radiation, conduction, convection, and evaporation. So let's first start. You do radiation. Let's talk about what is radiation. Now, we know that radiation is light waves.

right, emitted from objects. But some of those light waves have a higher energy and have heat dissociated them. What is it technically called, like a radio spectrum? It's a radio wave. Yeah. Which are, they're light waves. And so some have higher energies, which means they have contained heat. And these include things like infrared. Yes, which is mostly, in this case, it's infrared. So when you look at the sun, the sun is producing so much thermal energy

that it is producing all this energy in a whole magnitude of wavelength. That's right. We can see some, which is the visual light spectrum, but also there's the infrared, which we can't see. We can use cameras. Some animals can see it or perceive it, but we can use cameras to pick that up. And I think, correct me if I'm wrong here, but I think every matter in the universe produces infrared unless it's at absolute zero. Right.

And that's the way that sometimes, cause I'm with Zarina who's four years old. She's learning planets at the moment. That's her daughter. My daughter. And so she's interested with Neptune and they. Not your anus. No. I hope not. So, um, they're talking about the temperatures at Neptune cause it's a, an ice giant. Yeah. And I'm thinking, how do they know that temperature when they've never been there? Yeah. Right. And,

And it's just through infrared spectrum. They just can see everything, even like ice still gives off infrared. Yes. Okay. Just obviously less than what we would as 37 degree humans. Yeah. But the infrared is emitting this form of radiation, which we can pick up. Yes. And so we are, so the form of radiation of,

Heat loss is we are radiating heat out of us. So I'm sure we've all seen infrared cameras where you can see different parts of your body with different colors. That would indicate higher energy amounts in the infrared spectrum. Yeah, losing heat via infrared. And so this is into the environment, into the ambient environment. So while we're sitting in the room, 60% of our heat loss is in this form. As long as the room is at a lower temperature as our cells are.

Yeah, and it's happening without any surface contact. No, that's right. As long as the walls and the roof and the floor and the ambient environment itself has a lower temperature, then effectively it's going to radiate off you into that room. That's right, in that gradient. Okay, so that's 60...

At rest, pretty much that's 60% of your heat loss is occurring through radiation. All right, let's have a look at conduction. So what is conduction? This is through physical contact with another surface. So let's just say, let me, hypothetical. We go hiking. You've convinced me to go hiking out in the...

Gold Coast hinterland in the middle of winter and you said, look, it's going to be a pretty hot day. Don't worry about wearing any jumpers or long pants. Just wear shorts and a t-shirt. We'll only go for a couple of hours. We'll be back soon. Typical you, we get lost. You don't bring a map. I think that's the other way around actually, but keep going. Shut your mouth. We get lost because of you. And then nightfall comes. It's getting dark. Sun goes down. It's getting cold. Our body heat, we're losing body heat through radiation, right? With the external environment.

We need to stay warm. You say, Mike, there's no other way of doing this. We need to cuddle. And so through our embrace, the body heat of one shifts to the other because one of us is hotter than the other one. I think we know who's who. And that is conduction. Yeah, probably. Yep. Yeah. Or your bum on the chair.

If you're sitting on a steel chair and you're bummed, you're porky pig in it on the chair, the heat's been lost through your skin into the chair. Onto direct contact with the other surface. As long as it's not a moving surface. That's my only...

Well, hopefully the chair's not... No, no. But I just mean like... Because I was thinking about this. You know, like if you were like lying on a waterbed or something, right? You're lying onto a surface of water, but that water could be moving within that surface. So that becomes then convection. Well, no. It's conduction because you have to conduct it from your body into the mattress. And then from the mattress through the water...

That's convention. But okay, so we've got, so radiation is basic. Radiation and conduction are pretty much the same thing except one is into the environment without contact and the other one is into the environment with contact. That's right. And in the case of particularly exercise, we rarely will rely on conduction.

Yes, of course, because what are you going to be touching? And then there's convection. This is what you were talking about before. So this is the air going past. So this is basically air or water going past. Like another medium, I guess. Taking the heat away via air or water. So this is why you at the gym –

running underpants with a big fan in front of you. Well, yes. And people complain and you're like, it's convection. Well, you always pay people to just blow on you while you're doing exercise. They're just standing, just blow. Matt, you could have a fan. It's like, I'm not paying these 14 people to blow on me when this is ridiculous. So,

Yes, that's convection, right? Is the wind going past taking that heat away via the air or going for a swim? If you're swimming in water, you probably notice that as you generate heat, that heat gets dissipated quite well through convection. As long as the water's cooler, yeah. As long as the water's cool. Everything goes from a higher to a lower, whether that be pressure or diffusion or temperature. And you could see this, like if you were to do...

Look at cycling. Yes. And do outside cycling versus stationary. I'll do neither. Okay. If you're working at the same level of intensity, because you're stationary, there's no convection. Good point. But if you're out in the road, there is air movement. So you're better at removing heat. Regulating, that's right. Okay, so that's convection. Final one, evaporation. This is sweating.

Yeah, but well, yeah, I suppose it's water vapour, right? And a big part of that is sweating. So this one becomes the most important?

in exercise because this one really ramps up to then control our heat loss. Yeah. At rest, evaporation is still 25%, right? So right now, even though 60% of our heat loss is happening through radiation, 25% is through evaporation, but that goes up significantly with exercise. So you're right. A lot of it is through sweat.

You know, various glands, eccrine glands, for example, producing sweat, which has a combination of both water but also electrolytes, so salts in them. And we need to evaporate that off. Now, there's a couple of... Just one final point I will make. Yes. The first three, radiation, conduction, convection, all...

they rely on the gradient to be there. Just like we had from the core to the skin. Yes. They also need the gradient. So the reason I'm bringing this up is if the temperature outside is the same as our skin temperature,

you're going to now lose the gradient. But all of them rely on the gradient, actually. That's true. But evaporation, as we'll see, you could be in a room that's hotter than your skin, but the process of the vaporization is a cooling mechanism and that can still cool you down. The issue that comes about with evaporation is when there's so much humidity and we can no longer break the molecule of the sweat that it

that it loses that cooling mechanism, but you could effectively be in a room or an ambient space of say 40 degrees and,

So it's hot but humid. You can't do the radiation conduction convection anymore because there's no gradient between your skin going out into the environment because the environment's hotter. If anything, you're gaining heat through the radiation of the outside environment. But if it's the dry heat, you can still rely on the evaporation process for heat loss. But if it's hot and humid... Yeah, then you're in a lot of trouble. You can't get evaporation either. Right. So...

All of them are reliant upon what the temperature and humidity is of the external environment. But in all honesty, effectively, because evaporation is about sweating, you, through exercise, will have triggers that will stimulate sweat. So the more you exercise, the more you will sweat. That's right. So effectively...

Evaporation is a product of exercise intensity while the other ones are simply a product of the ambient environment, right? In terms of their effectiveness, that's right. Yeah. Well, in terms of their effectiveness, but in addition to that, while you exercise and you produce more sweat...

it increases the likelihood of evaporation. But if, again, there's always like a threshold, there's always like a limit. If it is too hot or too humid, and we'll get to that, it will just stop that evaporation. Because if the environment is- Particularly the humidity, that's a big killer. That's the killer, exactly. All right, so evaporation via sweat, right? It depends on a couple of things. So this is sort of a nice little lead into. It depends on, again, the ambient conditions, so the temperature and the humidity. Okay.

It depends on the skin surface area. How much of your skin is exposed. That's right. Yep. So if... And then you'll see this with... You had a shirt on or didn't have a shirt on while you're running. Well, you'll see this in... Well, I'll throw it to you. Which sport do you think would need to produce the most sweat? Which athletes in which sport...

Do you think have the biggest issue with thermoregulation and therefore producing the most amount of sweat? Equestrian. For the horse? The horse, yeah. American football. Oh, right. Now, it goes to that principle of the amount of skin exposure. Yeah. Well, they're wearing big suits, right? A lot of suits, a lot of padding, helmets. Yeah. So they haven't got... A pair of underpants. Yeah, that's...

Well, you would have to in the size of those guys and then smash it into you'd be having to change your pants all the time. So they are at the highest risk potentially for overheating. And interestingly, I would never have thought it'd be possible. But some of these guys, because they have such a big volume to surface area ratio. So more volume to surface area. You're saying they're big blokes. Big blokes. Yeah. With a lot of padding. Yeah.

and a lot of skin covered, so they can't do a lot of these processes we spoke about for heat loss. They need to sweat, this is probably at the highest level, something in the region of four litres an hour. Four litres an hour? Yeah. I mean, we've only got...

six liters of blood in our body. Sure. We've probably got, you know, dozens of liters of water in the body, but that would mean that you're losing so much fluid that effectively, you know, if you lose 1% of your body weight, one to 3% of your body or one to 2% of your body weight in water, that's going to disrupt your performance significantly. If you lose any more than 2%, it's going to,

disrupt physiology. That's right. Heat. And heat stroke. It's called heat illness, which is a spectrum that ranges anything from kind of what's the lower, the worst is heat stroke, which is, um, can be lethal. Yeah.

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all the way down to the lowering, which could be kind of heat syncope, heat rash, those kinds of things. It's just not keeping heat, kind of gaining more heat than you should. But they're pushing that. They're pushing that, yeah. And I remember there was a case that we spoke about, I think we did a conversation article on this, and it was an NFL player who died from heat stroke. Yeah, that's right. And in pre-season. And it was just day after day of training him

high humidity. Yeah, I remember that. And just had the early signs, but then he didn't, I guess, replenish enough for the next day. And then he went into heat stroke, which is essentially the core temperature becomes over 40 degrees. Yeah. And you start to develop neurological symptoms. And then that goes down into coma, changes in cognition. And then if not rectified, then death. All right. So before we jump into how we replenish and all those things, um,

the way that evaporation via sweat, because we sort of took a bit of a tangent here, evaporation via sweat, that depends on, again, the ambient conditions, so the temperature and the humidity, the skin surface area that's exposed, hence why the conversation about the football players, but also the convection currents. So...

Is there a wind going past? Are you doing it in a closed room? Right? So are you doing it in a swimming pool? So those convection currents matter. So what's coming past to take that heat away? Humidity is by far the most important factor. You said that earlier, right? And the reason why is because of it reduces something called evaporation pressure. Or vapour pressure, yeah. And so this vapour pressure...

So sweating in itself doesn't cool the skin. No. Right? It's the evaporation. That's right. That's just putting water on top of your skin, isn't it? Yes, exactly right. So if you're in an environment that's too hot, too humid, and you're sweating like a pig, you may not cool down. You're just getting sweaty. One, you're losing fluid. So your performance drops. You might get sick or unwell if you keep doing this without replenishing and you stay hot.

Because you don't have, one, you don't have the lower humidity and temperature. Two, you don't have convection currents taking it away. And three, you don't have the surface area of skin exposed to the environment. So these are really important things affecting that evaporation. So...

Really interestingly, your body loses 0.58 kilocalories of heat per milliliter of evaporated water. So what that means is in one liter of sweat that evaporates, you're losing 580 kilocalories of heat. So that may not sound like...

anything relevant because it's kilocalories, but effectively kilocalories is energy and energy is energy and heat are effectively interchangeable. You could argue, right? So let's talk about, before we go into how we can cool ourselves down properly, right? Let's talk about storing the heat because whatever heat we don't get rid of through, you know, radiation, conduction, convection and evaporation,

By definition, we have to store. Yeah. Right? So how do we, you know, how does this heat storage affect the body? So what we know is the amount of heat required to increase the body temperature depends on the body size. So the bigger somebody is, right, is going to have an effect. And something called the specific heat. So Matt, can you sort of tell us what the specific heat is? Just it's the energy of just raising –

I mean, in this case, it's the tissue, the body tissue by a degree, right? Yeah, the amount of heat required to increase one kilogram of body tissue by one degree Celsius. And that's around about 0.83 kilocalories per kilogram of body mass. So, for example...

If I want to know how much, you know, how much heat is required to increase my, I'm 70 kilos, my body temperature by one degree, you basically go 0.83, which is, you know, the kilocalories per kilogram by 70 and it's 58.1 kilocalories. So what that's saying is that,

For every 58 kilocalories of heat I hold on to, my body temperature goes up by one degree Celsius, right? So it's just a – it may not have a lot of relevance to the listener, but it's an important fact to understand. Yes, that's right. And as you said earlier –

Once you just start to incrementally increase this temperature by a couple of percentages, then you're starting to diminish performance. Yeah. But you also get into a point if it starts to approach in terms of your core temperature,

Yeah. Yeah.

What triggers those processes to occur? So obviously, yes, it's a temperature gradient that's required from internal to external. But we also need, we know that we sweat. So we need something to trigger the sweat. We need something to tell the blood vessels to dilate at our skin, right? So that more blood gets to the surface of the skin. What is it that triggers that?

and vasodilation, you know, cutaneous vasodilation to occur. Yeah, it goes back to the thermoreceptors and also the thermostat. So it's the hypothalamus being the kind of central conductor of it all. Just like in an orchestra, this is the one that's kind of controlling it. And the information that's being fed from both the skin and the central receptors, thermoreceptors, need to be controlled

send in appropriate signals that it's receiving to know what kind of temperatures both centrally and peripherally. And then the way that it responds, it has different systems to work with. So it's got a vasomotor system, which is a neurological system that controls blood vessel diameter, but also it can then go to skeletal muscles. You want it to shiver on the opposite end or in the case of

Heat loss. Then we go to sweat glands. And there's different sweat glands, but I guess the most important one for us is eccrine. How do you pronounce it? Yeah. I say eccrine, yeah. Which are the most abundant on the overall surface area of the skin. Yeah. But they release their water into... Sweat.

The area, but the area of the skin that's away from hair follicles, whereas the other one, which is the apocrine, they actually release a sweat into a hair follicle. And so that's, you know, the scalp or in the axilla or the groin, they would be apocrine sweat glands, but they wouldn't be so useful for thermoregulation. They probably have other pheromonal factors.

Uses maybe. Yeah. Yeah. Totally agree. Totally agree. All right. So we've got the thermostat being at the hypothalamus, helping us sweat, helping us phasodilate once that's been detected. Like you said, if the temperature is too low, we shiver, increase the release of catecholamines or we can vasoconstrict at the skin or increase the amount of thyroid hormone being released. And we know that we've spoken about in other podcasts that fever can sort of tweak this. And so we,

We know that if you've got pyrogens released from invading pathogens... Or your own immune cells. Yeah, that's right. It can sort of just change that thermostat. That's the set point. That's right. Now, when you exercise, you can't really change that thermostat. Exercise doesn't really change the thermostat. So let's talk about the fact that when we exercise, we produce heaps of heat. So heat production is a product of exercise intensity.

So the more intense your exercise is, the more heat you produce. And so your body attempts to try and return your core body temperature to its set point, but it can't.

If you're doing moderate intensity exercise, you might be able to get close to it, but effectively when you continue to exercise, your body temperature will continue to go up and your body will continue to do all those things we've spoken about to try and maintain the body temperature. So

At lower temperatures, right? And when I say temperatures, I mean ambient temperatures. So if you and I are doing a workout now and the ambient temperature around us is lower, let's say 22 degrees Celsius, right? So a room temperature. You said this earlier, convection and radiation...

heat loss is far better. Yeah. Right. But as the temperature goes up, the ambient temperature goes up, they become pretty useless. You mentioned that earlier, right? Once the temperature, once the ambient temperature is so high that it's a sort of equivalent to our body temperature,

We can't release the heat through radiation and convection. So that's when we start relying on evaporation for heat loss. So we mentioned earlier that the more we exercise, it's a stressor. It stimulates the sympathetic nervous system. The body temperature goes up. It stimulates the hypothalamus. Those things together increase the amount of sweating and then evaporation goes through the roof, right? And so that is really important because

unless the humidity is too high. Then we can't evaporate because humidity is just the water concentration in the atmosphere around us. Yeah, so just to underscore that, so let's say you're in an environment of 50% relative humidity versus an environment of 100% relative humidity. If the temperature at the 50% was 30 degrees, your vapor pressure of the ambient is 15.9 millimeters of mercury.

Okay, now you compare that to 100%. It's now doubled it. That's the vapour pressure. So that's the pressure that's required for the water to go from a liquid phase into a gaseous phase. Yeah, a bigger push. That's right. It's a lot more difficult. So if we on our skin had a vapour pressure of 32...

Well, let's just say 35. Okay. That's what the vapor pressure on our skin is. 35. That does tell you at an environment of 100% humidity at 30 degrees Celsius, you've only got a gradient of about three. What's the vapor pressure? 32. 32.

So the vapor pressure of the atmosphere is 32. That's right. The vapor pressure on our skin is 35. So it's only going to go in a three millimeter mercury direction by a push in pressure, let's say. But you compare that to 30 degrees at a 50% humidity, it's only 15. So you've got now...

20 difference. So the gradient is so much more. So your ability to break the water molecule into a gaseous form and that reaction is a cooling reaction. So the blood under the skin where the reaction has occurred, it will cool it. And then that itself will be a form of kind of convection because it's kind of bringing hot temperatures to your skin. You have the evaporation and then you have heat transfer. Yes.

Yeah, in a way it's a tricky concept to get. I mean it's intuitive because we all undertake it, but water vapour can be a tricky concept to understand. But yeah, I think knowing that it's a product of your body temperature, like your skin temperature,

and the temperature of the environment around you effectively, you just have to think about it as though the, the closer you are to the temperature around you, the harder it is to evaporate. Right. And that's it. And if you're training in a cold temperature, the easier it is to evaporate. Um,

And then that humidity also comes into play. So what if we're exercising in a hot environment, right? So obviously you're increasing your risk of hyperthermia, not hypo, hyperthermia and heat injury as the temperature goes up, as the humidity goes up. Yeah, that's right. You said before that an American footballer can lose four to five liters of sweat per hour. Right.

Which is phenomenal. Which is insane. But it's also different per person. So yes, it's different by sport, different by intensity, but different by person. So you might sweat more than me at the same intensity. So genetics seem to come into it. It used to think that it was sex difference between male and females, but that's been kind of disproven. Once they kind of look at...

all the other contributing factors and have been attributed to that, particularly acclimation, because some athletes might be better heat

what's the word, acclimated than others, and that's going to play a difference. But genetics is obviously big, an important player, but also surface area to volume ratio is also important. That's where, say, infants, they would have a greater surface area to volume than adults, so that might be a little bit better advantage

getting rid of heat and that probably becomes more of a problem in the cold environments because they can lose heat quicker than adults. Yes, absolutely agree.

So how do we avoid, you know, this process of dehydration, right? We said that if we lose one to 2% of our body weight in sweat, it decreases performance. But if we lose 3% or more, it's going to result in heat injury, which you mentioned earlier. So what can we do to avoid dehydration? I know that, you know, one of the things we can do is drink 400 to 800 mils of fluid, you know, in that three hour period.

time period prior to exercise, but what else can we do? So that would be kind of, you knew that you're going to be exercising in a hot human environment. You'd have to preload yourself, prehydrate yourself before any kind of activity. You would want to also be mindful of when you're doing the exercise, if you can avoid it. So if you were wanting to train, um,

In the summer months. Yeah, at 12 o'clock in the afternoon. You'd choose it in the cooler parts of the day. Right. You'd have your breaks. You would have drink breaks. You'd have breaks to sit down in a cool, shady environment because, again –

The sun is producing radiation. The concrete or the outside surfaces are producing radiation. So you're getting in the opposite direction. So you could be gaining heat through radiation from the outside environment. So you're going to be mindful of that as well.

Yeah, and just be mindful of the amount of fluid loss you're having. So sometimes athletes will weigh themselves before and after a session, and if they notice that there's a weight loss, they would have to replenish that weight with fluid by 150%. Yes. So if you lose a kilo, you would assume that's a kilo loss of fluid, so you'd have to – a liter and a half to replenish that. Yeah, and –

If you are exercising intensely, right, in hot temperatures, try and consume 150 to 300 mils of fluid every 15 to 20 minutes during that exercise. That also goes to the choice of liquids. So again...

You'd have to choose. I do hot chocolates. Yeah. So they seem that the best choice of fluid is something that's cooler and something that you like a taste of. Makes sense. So something a little bit more sweeter. Now, that's not me trying to say, oh, therefore you should load it up with any particular agent. But generally speaking, something that you like and it

and more likely to engage with something that you're more likely to drink. Yeah. Yeah, absolutely. And this kind of also speaks to the production of Gatorade, right? So Gatorade being a sports drink that was developed for NFL. Yes, that's right. And so that now makes sense that, so the Florida Gators being in Florida, hugely humid down there. And I'm guessing this probably come about in their preseason, which is summer. And Gatorade,

they are losing so much fluid through sweat and there are scientists that are working with them. I think that was associated with the University of Florida. We're trying to figure out what liquid is the most efficient at hydration. Now, obviously water is great and we should be generally trying to drink most of our fluids through water. But when you're losing so much amount of fluid like that,

Water's not as efficient as other liquid supplements, let's say, because as we spoke about previously, if you ingest water with electrolytes like glucose and salt, it will actually promote the movement of water more efficiently than just water on its own. And that's where the electrolyte drink Gatorade came from, which is named after the football team. Yes, yes, exactly. And it's going to increase hydration. So it's a big factor.

Let's have a chat about how training in a hot environment impairs performance. So how well you're performing during that exercise. So let's talk about what's happening to decrease performance in the heat. So three things happen, right? Let's try- Or three effects on systems. Yeah. And these are the things that tend to influence fatigue. So one is when you train in the heat, you're accelerating muscle fatigue.

So we spoke about muscle fatigue in a previous episode and all the various factors that influence it, you know, the pH, the ATP production or ADP production, lactate, all these various molecules sort of influence muscle fatigue. Number two is cardiovascular dysfunction. So the cardiovascular system can change, but then also central nervous system dysfunction. They don't sit in isolation. No, they all happen together. Yeah, and affect each other at the same time as well.

So again, muscle fatigue. What's happening to increase muscle fatigue?

during exercise in hot temperatures or hot environments? Well, they found that there's an increased rate of glycogen breakdown. So this is the stored energy within muscle. And we found that in higher intensity exercises, that when you are performing these activities, the muscle is utilizing glycogen more predominantly than

than other energy sources. So if you burn through the glycogen, in this case, heat is having an impact on the way of the amount of glycogen that's available for energy production during this

exercise. Therefore, as you burn through it all, your ability to keep performing an exercise starts to drop. At the same time, we're seeing that there's more lactate within the muscle. Now, I'm not sure if it's the result of lactate being there or the processes that's leading to the generation of lactate that diminishes. The latter. Yeah, it's definitely the latter. Yeah.

And then we also just have free radicals being produced, which oxidizes certain muscle proteins that then diminish the performance or the efficiency of the contractile proteins. Just to talk about that lactate, when...

the presence of the lactate is probably more so just indicating the presence of an acidic environment. So it's probably more so the acidic environment than it is the lactate that's contributing to the muscle fatigue. So yeah, increased rate of muscle glycogen consumption, decrease in pH, so acidic environment, and an increase in the free radicals that are being produced, which we know can steal electrons off the proteins, including the contractile proteins. So that's accelerated. So heat,

Can do that, can increase all those things. What about the role of heat on the cardiovascular system and how that then impairs performance? Well, as one thing we spoke about, we're sweating a lot here. Yeah, true. So as you're losing a lot of fluid, you're going to slowly take away your volume of blood that's returning to the heart.

So that just means we've got less preload coming to the heart. Therefore, that directly impacts stroke volume and that then directly impacts cardiac output. So just our ability to keep, particularly if this is an ongoing in duration, we're going to slowly drop the efficiency as we continue the exercise. Now, adding to that,

A bit like what we saw, I think it was the respiratory system when we said that as you start fatiguing your respiratory muscles by higher intensity, you're taking blood away from the exercising muscles to the respiratory muscles. The same goes here with thermoregulation. You're taking blood volume away from the muscles to the skin because you're trying to get rid of the heat.

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Oh, there's a competition. The muscles are contracting saying we need the oxygen and nutrients, but at the same time you're producing so much heat, which can only be dissipated by the blood that it says, yeah, but I also need to go to the skin to get rid of this heat. So now you've got a trade-off and more blood has to go to the skin to get rid of the heat.

So the muscle doesn't get it fatigued. That's right. That makes sense. And putting these two together, you're starting to fatigue your central nervous system. So the central nervous system is going, well, this is getting really hard. That's because it's detecting all these things as well, right? So afferents are being sent. Yeah, afferents. So you're getting all the sensory signals coming from the muscles. So this could be thermal as well as chemical. It goes to the brain, which then impacts the primary motor cortex, which kind of says, hey,

Just slow it down a bit, you know, and then you've also got the psychological motivation to do the activity. Oh, that's true. Yeah. Which also you'd have to be a very strong mental individual here to kind of push through all this. So most individuals will slowly drop the want and will to continue the activity. Yes. Oh, that makes, I mean, those things make total sense. So heat's influencing all that. So then my question is Matt, can we,

you know, and I'm going to speak on behalf of athletes, you know, considering I am one. I wish I was. Can we acclimate to the heat and therefore reduce those effects? So can I... Can I ask you a question before that? Yeah. What about hack? Can we do any hacks to help this in the short term? So this would be like pre-cooling.

So we spoke about certain hacks to get around the acid-base balance with some of those supplements. Bicarb. Yeah, bicarb and then also hyperventilating. Could we do the same with temperature here? Could we just jump into an ice bath?

and get our core temperature down to, I don't know, 35 degrees before we do the exercise? I mean, theoretically, yes. But you need to realise that, again, the –

diminished performance occurs on both ends of the temperature spectrum. So it's not just high temperatures reduce performance, but cold temperatures reduce performance. So what you want to become is just more efficient at maintaining core body temperature, not be as cold as possible before you begin. Because as we know, if your muscles are cold, they're not going to contract well enough because blood flow is going to be reduced.

Blood flow to the hands. Dexterity is going to be reduced. If you're playing something like football or cricket and you need to catch a ball or hit a ball with a bat, it's going to be reduced. So you just want to be better at maintaining core body temperature. So therefore, you need to be better at –

without removing the excess heat. Have you ever come across people that kind of use like ice vests or things like that? Yes. Yeah. I mean, if you're using the ice vest during the exercise, then of course it's going to help because it's going to help with the, that's going to be part of that convection, right? Or conduction, you could argue, because it's in contact with your body. You know, running with a shirt off,

is going to be superior than running with a shirt on in regards to heat loss because you've got more skin exposed for evaporation to the convection, so the air that's moving. Depending on the time of the day and the sun as well because there's a couple of variables there because you don't want to be getting third degree sunburn at the same time. No, of course not, but I'm just talking from a pure perspective of heat loss. Skin exposure, yeah. Right? So...

So a bit like the supplements in the acid base, there's probably some benefit there, but again, it has to be very well controlled and thought through. Definitely, definitely. So let's talk about, can we talk about heat? Yes, sorry. No, no, no, that was a great question. Heat acclimation, right? So let's first just define acclimatization and acclimation. Effectively, they're the same thing, right? They're physiological adjustments to the natural environment, but what's

But one is over a long period of time, that's acclimatization, and then one is a short period of time, and that's acclimation. So let's talk about acclimation mostly. Let's just say you're an athlete. Thank you. Again, hypothetical. You're an athlete and you live in Victoria.

Australia, it's winter, it's cold, it's windy, it's wet. It's not nice. Sorry, Victorians. But you now need to go to Honolulu. You need to go to Hawaii. The Ironman. Straight away to do the Ironman, right? Now, same time of year, it's summer there, winter here. So you decide to go a week early, right? Let's say maybe you were intelligent enough to go 10 days early.

Can you train in that temperature and get your body acclimated so that you perform better? Meaning you're acclimated so that you don't overheat the way that you would if you simply just went straight from Victoria to Honolulu and did it the next day.

Is it possible? Yeah, yeah, definitely. To give you an answer, yes. And it can be done relatively short term. So we're talking seven to 14 days. So this 10 days is a good time period then? Almost like I'd plan that. Yeah. And all individuals theoretically have that ability to acclimate.

I think the main important stimulus is just core temperature. So as long as you are, when you're training, able to get your core temperature higher, therefore your body physiologically will acclimate to that stressor.

Yeah, it makes sense. You expose your body to the stressor so that it can respond to it so that next time it's exposed to the stressor, it doesn't have such an issue, right? And there's a wide range of different physiological things that is going to occur with the acclimation. Yeah, so before you talk about those things, the whole goal of the acclimation is to...

drop core body temperature and reduce heart rate, right? Like that's predominantly all the things you're about to say that are the physiological adaptations that occur in acclimation is to reduce your heart rate and reduce your core body temperature. Pretty much. So-

Processes that get rid of heat and maybe processes that generate less heat. Yes. So what are these? What does your body do, Matt? You go to Honolulu, you start training for those 10 days for that Ironman. What does your body do to acclimate? One of the first physiological things you'll notice is you'll get a change in heart rate. So your heart rate...

will drop. So like resting, but also performance heart rate will drop to a lower amount. And that's important because as we spoke about, I think in the cardiovascular, if your heart rate's higher, this was a big difference between an athlete and a non-trained person. If your heart rate's higher to keep that cardiac output, the heart is actually working hard and that's generating metabolism. Therefore it's causing, in this case, a higher temperature. So if you can get the engine to work less,

That's going to produce less heat. So heart rate amount quantity is going to be less in a person who's acclimating. That's one. Another one is just the amount of plasma volume that's in your system. You will produce or have more plasma volume

percentage-wise as you start to acclimate, which is again good because that gives you more ability to distribute heat through sweating and those processes by also retaining more

volume or cardiac output whilst performing. Then you're going to go more to the sweating side of things. So as you start to acclimate, you also will sweat earlier. You're almost pre-sweat. So you're kind of pre-cooling in a way before you perform the exercise, but then also your sweat rate, the amount of sweat that you perform is higher in the activity. So you're becoming more efficient.

Now around that, because you're sweating more, you're losing mostly water, obviously, but also the electrolytes. And you need to be able to be better efficient, more efficient at retaining the electrolytes. You don't want to be losing all the sodium chloride. So you become more efficient in your...

hormonal regulation system and this is aldosterone which is holding on to salt holding on to water so your kidneys are doing some stuff here as well finally you've got heat shock proteins which are stressor hormone stressor proteins right so this could be through any kind of injurious agent

the cells will be releasing these proteins to kind of protect the cell from being injured and dying. This can come from a number of things, but in this case, this is thermal damage. So the cells just become better equipped at being exposed to high temperatures. So let's say you do all these things. You have these physiological adaptations that occur to acclimate. You perform the race, you head home, back to Victoria,

Do you maintain that acclimation so that if you were to go back six months later, can you just go back to Honolulu six months later and then do the Ironman again the next day so you don't have to go and do the 10 days again? No. Short answer, no. So you lose the acclimation. Pretty quickly. How quickly? Probably as quickly as you gain them. So again, probably all gone within a month. Wow. Okay. That's interesting, isn't it?

That goes back to the use it or lose it phenomenon. Yes, very true. Very true. The body generally doesn't want to hold on to things that are useless, not beneficial in the time because all these would probably just require more energy to keep them going.

What about when we train in the cold, right? So obviously when the temperature is, we've spoken about the heat so far, biggest factors, temperature and humidity, right? When we're training the cold, yes, we know that we can shiver. That's an involuntary muscle contraction that's occurring that generates heat, but we've also got the thyroxine and catecholamines that can produce heat. But when we're training in the cold, right?

My thought would be that, well, effectively when you exercise, you're producing heat and the colder the ambient temperature is, the better you are removing the heat. So training in cold environments are probably in a way better for heat loss. So maintaining internal body temperature. But obviously you can have it so cold, right, that it's –

going to have some detriments. So for example, it might be so cold and you haven't worn the appropriate layers or whatever it might be that the cold air will

really significantly influences blood flow, right? Particularly to the peripheries, hands, feet, right? That can lead to not just pain, but loss of dexterity, might alter the way that you run, might alter the way you capture, hold things, use things within your hands. So for sports that rely on dexterity, like we mentioned earlier, probably not a good thing. Is there anything else that the cold temperature can affect

Yeah, like you said, if you're exercising particularly at a high intensity, you're generating so much heat and chances are in a colder environment, not super sub-zero, you have a better way of dissipating the heat. It allows you to probably perform the exercise better. But at the same time, because your outside body is exposed to an element, you don't want to be going the opposite way where it's going to cause damage to the outside body. So frostbite would be a concern. So you'd still want to...

in an appropriate fashion that you're not exposing your body to the elements. But at the same time, you don't want to put so much clothing on that it then hampers the dissipation of heat. Yes. So frostbite becomes an issue. Hypothermia. Yeah. But generally in the air, when you're just exposed to the air as convection, it's not going to be such a bigger impact than what

It's cold water. So if you were doing cold water, like 15 degrees, it doesn't have to be that cold. Like it doesn't have to be. And I think this is where the cold immersions come into now. Like once it was like ice baths, but I think the evidence is starting to go now. It doesn't have to be that cold under 15 degrees is maybe enough.

Celsius. Yeah, Celsius, to change that relationship. So even being long duration swims in 15 degree water could be enough to change your inner body temperature because you're losing too much heat to the outside, but you're also bringing cold into your body. Yes. So can we acclimate to cold temperature the way that we can with hot temperature? We can. Okay.

But from my understanding, it's not as profound. So certain things can take place. What was the method of generating heat? Shivering and non-shivering thermogenesis. Yes. So those processes you...

Probably become more efficient at, but you don't rely on shivering at a particular temperature. What your body can actually do is it can kind of conserve heat better. It's idling at a higher reverent. That's right. Before it has to kick in the shivering compared to non-acclimated individuals, they can kind of conserve heat better. You see that, right? I go to Tasmania.

And I'm shivering before my friend that lives in Tasmania does. Right? Same temperature. Our skin's probably the same temperature, but it's triggering my shivering because I haven't acclimated to that temperature. And then also the body composition plays a role here. That does have an insulation effect. And so individuals that have a bit more body fat will be better at conserving heat. That's generally why they usually say women are better in the colder environments because

than men because they have a little bit more subcutaneous fat proportionally. Yes, and the way it's distributed. That's right. And then finally, even this one I wasn't aware of, but sleep in the cold. If you are shivering, you're not going to have a very good sleep. Well, that makes sense. Just don't sleep in the cold. So individuals who are cold acclimated generally have better quality sleep, which probably then impacts their performance. That makes sense to me. But I remember...

Working in the States, when it would get really cold, so under zero Fahrenheit and beyond, we would be out skiing and you'd be all covered up, but where your face was exposed, particularly in the kids that I was instructing, they would start to get, their cheeks would go rosy red. Oh, yeah. And then they'd start to get white spots, which is the starting point of frostbite. Really? Oh, boy. So you can only really be outside.

That was, you know, in really cold snap periods, like negative 20 plus. Negative 20? And below. I've never been in negative 20. You'd only be out for half an hour to an hour and you'd have to get inside, be starting to get frostbite. Wow. I mean, I remember when I was doing my PhD, I lived with a bunch of Europeans and in old Queenslander houses, which, you know, you can see through the floorboards, right? So it's not a well...

temperature regulated, right? It doesn't have great insulation. At least for the cold, right? At least for the cold, exactly. I mean, it's built for the heat so that the heat through... Convection. Yes, exactly right. Airflow.

But that would say to me, these Europeans who obviously have very cold winters, the coldest they've ever been is in Queensland. Perceptually, yeah. Because the buildings are not made for the cold temperatures and it would be freezing. And you put a heater on, it dissipates the heat because that's what the buildings are made to do. And it is. It's freezing and you don't get a good sleep. Very true. Maddy, that is...

To be honest, we spoke for a lot longer than I thought we would go into on temperature. It's an interesting topic, but at the end of the day, you know, in order to – we're better at losing heat than we are maintaining cool, if that makes sense. So we generate it, we get rid of it, but it's hard to get rid of if the ambient temperature and humidity is too high. That makes total sense. And we said that particularly here, right? Yeah.

Where we live in Queensland. It's hard to find in Queensland. It is humid in summer and it's... Yeah, go for a run. Even just like doing activities outside in summer. Yeah, hard work. Hard work, but also, I'm not sure about you, but you lose the motivation of wanting to do it. Not me. I've never lost motivation once to do anything, except maybe record this podcast with you. Luckily, you're acclimated to it over the last seven years.

Seven years. I reckon it's close to eight years now. We've been doing this for a while. All right, Matty, thank you. Everybody, thank you so much for listening. This is, I don't know, episode 10, I think, of our special editions. Potentially the last. Maybe the last. We'll see.

Please, if you want to send us an email, do so. It's admin at drmattdrmike.com.au. There are a couple of emails there I still haven't got back to. I do apologize. If you have a question for us that you'd like to address on a Q&A, please do so. But remember that we are not medical doctors. We are not here to give you health advice. We are here to provide health information. We are only...

I'm here at Thames. That's right. That's right. Well, not only. We do many other things, but we're here to help educate, and that's our job. So we want to teach anatomy and physiology, and to do so, please send us questions. Please give us a five-star rating for the pod. Please go onto our YouTube channel and subscribe. Watch our videos, like it, comment, share with friends. It's wonderful. I love hearing students from all over the world.

Can I tell you a very quick story, Matt, about- I think you can go on anyway. I was at a staff retreat this week, start of the week. So it was a planning day for the next few years for the health group of the university that I'm at. It was a great event and there was a colleague who their first day was that day, right? Oh, okay. So that was their very first day and I was talking to her and she said that her daughter is at another university studying biomed. Right.

right? Biomedicine. And their first year. And I said, I bet you that your daughter has watched my videos on YouTube. And she's like, oh, okay. I said, my videos are pretty popular. I said, I think most students who are studying health in some regard, at least in Australia and the US have watched these videos. And she goes, okay. I said, send her a message. I said, ask her if she's watched Dr. Matt, Dr. Mike.

And she goes, oh, okay. Like she's very like, you're a weirdo. I'm unimpressed here. And then, you know, five, 10 minutes goes past. I'm off talking to somebody else doing something. She walks up to me. She goes, oh my God, read this. And she holds her phone up to my face. And there's about 10 texts going, oh my God, Dr. Mike saved us through our medical degree, saved us through the first year of our degree. Those videos are awesome. Take a photo, send it to us. And it was great. It was really nice that these students

students are watching what we're doing, watching our videos. The first time. I'm appreciating it. A colleague of yours had respect for you. And that is where I say goodbye, my friends.

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