Exercise Physiology | Exercise and the Immune System (Part 5)
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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 we are joined today by a special guest. And I mean, hate him or love him, it is a federal election year. We are approaching election time and we are joined by...

Leader of the opposition, head of the LNP, the Liberal Party here in Australia, Mr. Peter Dutton. How are you, Peter? Hi, Michael. Many people don't know this, but I'm the youngest of three. Oh. Both my parents are older. Right. Okay, Peter. Hi.

Good job, Pete. Look, I think we might. Thanks for coming. It was great to have you. Really great conversation. I might bring Matt back. Thank you. I think I actually sound more like Brita Harvey Canberra. Maybe, but don't forget to shut the door on the way out. Matty. Welcome back. Oh, there you are. Oh boy. You know, Peter Dutton was in here before. I saw him on the way out. Did you? Did you say hi?

Briefly, briefly. Oh, did you? I was going to say, I'm surprised you did. So we today, Matthew, my friend, we're going to be talking about exercise in the immune system. So this is part of our ongoing series, taking a look at exercise physiology. And

And we've spoken about a whole bunch at the moment. We're going on now, exercising the immune system. We're going to be talking about things such as... The immune system. Good point. But in addition to that, in what way does exercise affect the immune system? Does it improve it or is it a detriment? Does it change our risk of infection? And also, do different types of exercise in regards to their intensity and duration alter our immune system in any way? The answer is yes, it does. And...

And the age old question, Matthew, is should we train when we're sick? We'll leave that to the end just so everybody stays. Where do you think we should begin? Well, I think we should give an overview briefly of why we have an immune system. Right, because-

Right, because obviously our listeners are idiots and they have no idea why we have an immune system. But no, you know what, Matt? Let's be condescending to them and let's talk about why we have an immune system. You can do that. I'll sit back and watch. It's all about homeostasis, Michael. Well, it always is, isn't it, when it comes to health and medicine? It's boring, isn't it? Look, no, no, it's not because it's all about maintaining the happy, healthy balance. And if we don't maintain homeostasis, we get disease.

So, in what way does the immune system help us maintain homeostasis? Well, most people would assume that it does that by preventing us getting infected by microorganisms. Are they wrong? Mostly correct, but there's other...

aspects to it. So yes, that's true. We do have a lot of things growing on us and in us. Well, I mean, some you can't see, but when I look at you, I can be definitive about that statement. Shave that beard, please. So yes, we have microorganisms all over us and in us, which are important for our health. So we need those there. But at the same time, we've got to ensure that they don't become

Too dominant. Yeah. And they don't become pathogenic. So we have bacteria, we've got fungi, we've got even viruses growing on and in us. And to some degree, we need these, particularly the bacteria. And in your case, tapeworm? Well, yeah, Larry's been with me for a while now. I think, in all honesty, I don't know how much of me is me and how much of me is him. I don't know if...

I am a part of Larry or Larry's a part of me. Anyway, we'll talk about Larry later. But yes, you're right. We've got these organisms that live with us. And generally they are symbiotic, right? Okay. So we work in harmony. Yeah. We provide them with something and they provide us with something. Yeah. Yeah.

Oh, so keep going. Sometimes they become rogue. So that would be termed opportunistic. So they take an opportunity to then become, I guess you'd say, pathogenic. Like Staph? Yep. So Staph is a common Staphylococcus aureus, which is golden Staph. You did a good job. Okay. Usually is known to be a topical...

a type of bacteria that grows on our skin. But if we were to have surgical intervention, surgery, where the surgeon would put a hole in our skin, it has the opportunity to get inside. Yes. And in combination with a reduced immune system to help keep it at bay. So our immune system helps keep these potential pathogens at bay. Yeah. All right. So let's go into a bit more detail. And then you have the possibility of...

pathogenic microorganisms is coming in from the outside world into you. Yes. And that's where you need an immune system to prevent that. Now, outside microorganisms, there are other things that the body has to coordinate and that would be things like when cells aren't functioning as they should or they may actually be becoming quite...

or nasty like cancer-like. So the immune system is not only protecting us from invading things but also protecting us from within, from the body just creating some stuff that might not – so damaged cells that –

Might be produced in the body. Maybe when we reproduce a cell, we accidentally put in a mutation, a spelling error, and that could potentially lead to cancer. This happens a lot. So we need to be able to detect and remove. And so therefore we need a very vigilant immune system to get rid of that. And this is part of the reason why cancer, for instance, is more common in older age. It's because our immune system, as we get older, which is immune senescence,

is not as good and it can't clear it as well. In combination with the fact that the longer we live on this planet, the more likely we are to induce errors into our DNA. So let's talk about the immune system and its various divisions. Are we cool with jumping in now? Yep. Okay. So the immune system has two divisions, the innate immune system and the adaptive immune system. The innate immune system, how would you describe that?

Non-specific, always there. Okay. Does the same thing regardless of what the thing is it wants to get rid of. So whether I throw a bacteria at you or a virus at you, the- Or even just an injury. All these innate defenses will be the same. Yeah. Okay. And then how would you describe the adaptive then? Something that becomes specific to that organism, something that retains memory, something

A little bit slower. And it's sometimes referred to as the acquired. But I don't like the term acquired immune system because it makes it seem like it's not there and then it is. But the acquired is referring to...

an unknown antigen and then developing a memory to it. That's the acquisition that it's referring to. But I like adaptive because it is there and then it adapts and changes to what's happening. All right. So if we look at the innate division first, right? So there's two broad divisions within the innate division, which is external defences and internal defences. Can we start with the external defences? First line, second line.

maybe. Okay. You could say first line, second line. So first line defences, again, I'm throwing bacteria and viruses at you willy nilly. You need to defend yourself from it. You've got external defences. What are these external defences? Well, the most obvious is your skin, which is just like a brick wall of skin.

Keratin bricks. It may be for the thing from Fantastic Four. Yeah. So it's just layers and layers and layers of keratin and it makes it difficult for the bacteria to kind of get past that. That's the epidermis. Yep. And that is in conjunction with certain secretions like certain fat and high acidity, which are certain protective mechanisms to protect

Keep anything that wants to grow on your skin at the top superficial level. Yeah. And in addition to the skin, what else is there? Well, then we have...

Besides the things that are excreted onto the skin. We'll talk about that. Like oil and sweat. Sweat's usually done it for another reason, but that can also affect. We'll talk about that. What's the other one? But then you have all the orifices of the body, which is the vulnerable points of the body where there's no skin. Okay. So there's the ear, the eye, the nose, the mouth. I'm just trying to look at every part of you right now. Can't see all of them. The...

The rectum? If you could, this is probably one of the reasons why we're not filming. And the external urethral orifice. Yes. And then also for females, then I guess the vagina. Yeah. So if we were to travel into these various orifices, nose, ears, mouth, so forth, all of them, we are continually exposed to what you could argue as being, you know, phlegm.

for lack of a better term, the external environment as well, right? So because the epithelium continues for a certain amount of time and distance through those orifices. Yeah, pretty much. It's still surrounded and the surface. Covered by epithelium. Yeah, that's right, all the way through. But it's a different epithelium because it's a mucous membrane. Yeah, I mean, yes. If we focus on...

The two big orifice going down into tubes, being the respiratory tract and the gastrointestinal tract, they will be mucous membrane. Now, how much of our – if I were to ask you right now, I wanted to make a rug of you, a rug of your skin put on the floor, and then somehow I'm going to make a rug of your mucous membranes, a very slippery rug, and put that on the floor next to it.

What's the size? What's the dimensions of these rugs? The skin would be two metres by two metres. Okay, two square metres. Yeah. Whereas the mucous membranes of your respiratory, gastrointestinal tract, urinary tract would be more like a tennis court in a bit. Right. So in regards to a physical defensive barrier, your mucous membranes by far are...

offer a more extensive barrier. Yeah. Okay. There's more surface area there. Yes. All right. So we've got for the external defenses, predominantly we've got skin and mucous membranes, but like you alluded to before, as a part of the skin and mucous membranes, we've got other things that are there to help defend us from external and internal pathogens, right? So we've got things like obviously the epidermis, which you alluded to before, layers of brick walls filled with keratin or layers of skin cells,

We've got glands, like you mentioned. So we've got oil glands, so sebaceous glands. You spoke about the presence of fatty acids. So there's these unsaturated fatty acids which are in these oil glands. They're not a very nutritious source of energy for pathogens. So it's making the environment a little bit inhospitable. It also has a low pH of around three to five. So again, inhospitable environment. But we've also got sweat.

Which its primary function is for cooling down. Yes, via convection. But there's salt in that sweat. And that salt makes it, again, inhospitable. But also when we sweat, it sort of washes away whatever's on the surface. So it can wash away any pathogens on the skin. But we've got hair and cilia. How do they protect us? Like you've got a lot of hair on your face. So I would think that that would be a bed of pathogen growth. But-

In what way does our hair and cilia protect us? Well, they're two different kind of cellular projections. Yeah, hair...

I don't know. I guess you'd say that's probably more of a remnants of our predecessors. Yes. Does that mean you're more closely related to them? Which probably has. Look, I think if you grew your beard, you'd have a more pronounced beard than I would. No, it'd just be darker. But look how sparse this hair grows on my face. I can do a very good Italian moustache, but I can't do a very good beard. What about eyebrows? Oh, yeah. Could you join them? Oh, yeah.

Give me three hours. Give me three hours. I would be able to join Monobrow City. Oscar the Grouch, here I come. All right. So we've got hair. So hair can capture, right? It probably has more of a function of the regulation again. Yes. Or at least once did. But in part it would capture, right? But then do you remember that we – I don't know. I think this might have been an ABC –

we did where hair on certain body regions, let's say armpits, genitals, is more pheromone-based. Yes. So it has a smell. Different type of hair. Yes. So that has a different function. Yes, that's true. And that would also impact what's growing there. And I think the secretions that's produced particularly under the arms cause

causes a different bacteria to grow there, which then produces certain byproducts that give the... Scent. Less pleasant smell of... Hey, speak for yourself. Each to their own. Underarm smelling, whatever the term is. Scent. Didn't...

Napoleon tell his partner, wife, not to wash for a number of weeks on preparation of his return? Yeah. Because he liked the smell? He said, I'm coming back, don't wash. Which I just, I don't know if they put that in the movie with Joaquin Phoenix, but when I first heard that when I was little. You threw up? No, I didn't understand it. I'm like, why would, that's, that's.

And then I grew up and I'm like, that is still weird. But anyway, so we've got hair cilia captures particles or particulates which might be holding pathogens. Let's say nasal hairs. Yeah. Part of mucus is that we have tears and saliva as well and they tend to have enzymes in them that can destroy. Antimicrobial. Yeah. And we've also got our gastric. And I know that we're talking external here, but-

Your gastric membrane is still recognised as internal. And obviously that's got a very low pH of between one to three. As I say to the students, technically if you – you wouldn't attempt this, but technically if you swallowed a piece of yarn –

and allowed it to process. Once it's gone through eight metres of your tube, it's still outside your body. So you could actually kind of floss it. Oh, Jesus. Well, I remember I nearly got in trouble at work because I was doing a lecture. This was when I first started. This was like more than 12 years ago. I did a lecture on the gastrointestinal tract and I said, students, today we are going through mouth to anus.

And they all looked at me very, and I said, sorry, I meant to say we are going through the digestive tract, starting at the mouth, finishing at the anus. Oh boy, I'm getting fired for this, aren't I? Luckily, nobody complained. Now that's the external defenses. Let's just quickly talk about the internal innate. We're still in the innate immune system. Sorry, everyone. Still in the innate immune system. Now we've got internal defenses. Effectively, there's three types of internal defenses. We've got cells,

and physiological. So the cells are our white blood cells, right? Now I'm going to go through the white blood cells. I want you to tell me what they do, okay? So I'm going to say a mnemonic. You're going to tell our dear listener what each mnemonic represents for the white blood cells and what each white blood cell does. Are you cool with that? All right. So the mnemonic is never let monkeys eat bananas. Okay.

The first letter of each of those words, like a good mnemonic does, gives you the first letter of each of the words you need to memorize. It also gives you the order from most abundant white blood cell to least. So never. Neutrophils. Let. Lymphocytes. Monkeys. Monocytes. Eat. Eosinophils. Bananas. Basophils. All right. Now let's go through. Neutrophils, what do they do?

So again, these white blood cells can form the innate or the adaptive. Yeah. Okay. But I'll tell you which ones as we move through. So neutrophils are a part of the innate immune system. So they are going to be nonspecific. Okay.

Their functions would be to perform a function known as phagocytosis, so that's eating things up. But they're also their most abundant, so about 40%, 45% of your white blood cells are this form of white blood cell. They're very common. They are usually the first responders. They're the first on the scene when there's any kind of injury or invasion from a microorganism. So they will coordinate acute inflammation, which is an important thing

physiological part of the innate response. Yeah. Physiological for getting rid of the injury, getting rid of the injury.

Injurious agent, but also clearing things up for repair. Right, right. Okay. So neutrophils, first in, gobbling stuff up. Brilliant. Lymphocytes. Lymphocytes, they're the adaptive ones, so they can be made of T and B cells. We'll talk about that specific shortly, but they are more adaptive, so they're more specific to the organism. Okay. Monocytes. Monocytes, they are, well, they are a white blood cell that will mature naturally.

they'll mature into macrophages, which is a big eater. So they'll do certain similar functions to neutrophils, but you could make an argument that they are the...

They're like the bridge between the innate into the adaptive so they can be part of, because they're doing the phagocytosis, they can be also presenting the antigen to the lymphocytes. Yes. So the way I say to the students is that monocytes are monocytes in the bloodstream. Then when they jump out, they mature into macrophages and they can be fixed or they can be wanderers. So resident or wanderers. Yeah. Eosinophils.

So these guys... There's a lot of overlap with eosinophils and basophils, right? Yeah. I guess you'd say with eosinophils, they will have a role in parasitic infections, but they will also have a role in chronic inflammation and specifically from a hypersensitive. So it's an immune-driven response. Like asthma, for instance, you'd see a lot of eosinophil accumulation in the bronchioles.

Basophils? Basophils, they can elicit an immune response, but particularly an allergic immune response. Right. Okay. Brilliant. That's great. Now, they're not the only cells. There's another cell type, which sort of doesn't fit within these categories, but it is part of the innate immune response and internal defenses. These are the NK cells, the natural killer cells. Want to tell us a little bit about these cells?

Well, it's all in the name. So they are innate. Natural born killer cells. They'll just go around killing anything that they deem as questionable. Right. So whether it's a cell that's infected with a virus, they'll then kill. If it's a cell that's not your own. So this is an important point in the immunity or the immune system is self, non-self. And if you are deemed...

To be non-self as a cell, you'll just get destroyed by probably these guys. They'll just see. They won't have certain receptors that they should that would indicate, hey, this is us, and they'll destroy it. If you are an immune, sorry, if you are a cell that's infected, they'll kill you. Or if you're a cancer-like cell, you'll get killed.

And one of the – well, two things that they can do, these NK cells, is that they have perforins and granzymes. So perforins put holes in, and if you're an invading pathogen –

you're going to have a cell membrane. You've got an internal environment, which generally is of a different concentration to your external environment. So if you poke holes in it, things will either spill out or stuff will rush in. Either way, it triggers the cell to die. And the granzymes actually also trigger the cell to die through a certain means called apoptosis, which is I think Greek for when the leaves fall off the trees in autumn. Lovely. Which is beautiful, very poetic.

But effectively, it means a programmed cell death. And that's what you want. You don't want to trigger these cells to just die by any means. Because like you said, if you tell them to just explode, then all their cellular products go everywhere and they can in themselves be pro-inflammatory, right? And cause pain. And cause pain and issues, a whole range of things. So you want to tell that cell, time...

time to die, and then it will trigger itself to die through a means of apoptosis, which basically just it slowly degrades its products so that it's not just spilling out into the environment. And so NK cells can also help with that. So they're the cellular components. We've also got chemical components. So what are some of the chemical components of the innate immune system?

Well, you'd say the chemicals that the white cells communicate through. So...

I guess broadly you would call this cytokines, which are cellular doers. Probably mostly are peptide-based, would you say? But saying that, they can also be fat-based like prostaglandins. They can also be glycoproteins. So I wouldn't classify them according to any structural means, just through their functional means broadly. But generally they are done through a communication method. That's the way that the cells can talk to each other from...

long distances. At the same time, you have certain chemicals that are released from the liver all the time. Some of these known as complement proteins or kinin, are they proteins? Peptides? Which some are released only during like inflammation and injury, and some are released all the time, but only get activated during injury and inflammation. So these are

chemicals that can complement, so they complement proteins, which I think is about 20 different proteins that kind of work together to do a number of things. They can, again, smash holes into pathogens or they can put like, you know how they, with the military, they just put those smoke grenades? Yeah. And that...

says, hey, this is where the problem is and then the immune system comes in and kills it off or they release a whole lot of chemicals in that area and the

the immune system comes in and can find their way into the specific region. The way I think about, so, you know, you've got the complement proteins and cytokines and both complement other aspects of the immune system, right? So the way I think about it, and, you know, it's a bit of a, again, painting with broad brushstrokes here, but the complement proteins tend to call in the innate immune system. So the phagocytic cells like neutrophils, for example,

and the cytokines tend to call in the adaptive immune system more so. Now, there's obvious overlap, but broadly speaking, that's how I like to think about them. But they both do very similar functions. All right, so they're the chemicals, the complement and the cytokines. What about the physiological way that we, through the immune system, can innately defend from invaders or issues? Well...

One of them is Fever. So Fever is a physiological response. Good song. And that's usually- Michael Buble's version of Fever. Very good. Better than the original? Yeah, I think so. Because he's just got that- Ba-ba-ba-ba. Voice. Ba-ba-ba-ba-buble voice. Okay. Do you want to start singing it? Moving on. Fever.

Fever in the morning? Yep. Fever all through the night. Fever. That's right. Anyway. So the way that fever is generated, obviously the control center for temperature is your hypothalamus. So that's miles away if you got an infected big toe. Or if you live in another state. Which is the big toe. Yeah. So-

How does the big toe signal to the hypothalamus, hey, we need the temperature turned up. We need to get hot in here. Chemicals? Oh, Nelly. All right, keep going. Now you're going to sing Nelly. So what basically happens is the immune cells that are first on the scene, like the neutrophils, they will be releasing certain chemicals. Broadly, these are turned pyrogens. Pyro meaning fire. Ogens means what to do. And these can be both...

exogenous but also endogenous. In this case, these would be endogenous, meaning made by your own self, but some bacteria can produce toxins which are also... Pyrogenic. Pyrogenic. Now, that goes into the bloodstream. Now, it's supposed to coordinate inflammation and...

in the big toe, but if you release it into the blood... Well, only if the big toe in this instance is... Well, that was my example. But it goes into the blood and so this is going everywhere and then it goes to the hypothalamus. The hypothalamus says, look, there's an injury somewhere in the body. I'll just turn the temperature up. Now, by turning the temperature up to instead of 37 degrees, now it's 40. This is going to... Well, 39. This is going to make the immune system more efficient, but it's also going to make it harder for pathogens to grow. Yeah.

So the fever's one. Another good one is inflammation. So inflammation is an innate response to any kind of injury. The reason why we have inflammation is to bring more blood to the area, more fluid to the area, which brings more white cells, but also to promote healing. So can I just say that inflammation is not necessarily a bad thing? No, it's a good thing. And so let me just say that...

Inflammation, well, you say that, but inflammation's like Matt. I invite him over for lunch. It's fine. We chat. We have a good time. But then he overstays his welcome. He's there for too long. He's no longer good fun. He's annoying. He's a pain and I need to get rid of him.

That's like inflammation in which in the short term, it's great because it triggers a whole flood of chemicals that can trigger not only the cleaning of the area, removal of any debris or bacteria, but also the stimulation of growth and development to regenerate that tissue. So inflammation can be good, but if you've got constant inflammation...

then all you're doing is just flooding the area of these chemicals that can actually ultimately impede growth of that tissue. So basically what you're saying is you invite me over for lunch, you want me to clean your house and repair some things, but just because I want to stay a bit longer, you're now thinking I'm a detriment.

You are coming over next weekend to chop some trees down. So just keep – this was a bit of a hint that once you're done, get out. All right? So that's inflammation and inflammation is a requirement. We need inflammation. But because inflammation has those cardinal signs, redness, heat, pain, swelling –

they can sometimes be annoying, hence why people take medications to reduce the symptoms of the heat, redness, pain and swelling. Probably not the pain really, anything. Generally it is pain that bothers people. All right.

So we've got our innate defences. Our adaptive, we're not going to spend as much time on, but because effectively the adaptive immune system is comprised of two, well, one broad category of those white blood cells, which are the lymphocytes, which are the T and B cells. So let's just talk very quickly about the T and B cells and how they are different to the innate division. So what makes the T and B cells adaptive? Yeah, so in terms of the B cell...

They're named B because they mature in the bone. Okay. Now, they are produced from the same stem cell.

as the others. Yeah. But they just kind of go down a different lineage. That's right. They go down more of a lymphoid lineage. That's right. So you've got your hematopoietic stem cell, which is sitting in the bone marrow. Yeah. And that cell can turn into every single blood cell basically. So that includes not only the white blood cells, but the red blood cells, the natural killer cells, and even platelets. Yeah. But...

Early in its differentiation, it can turn broadly into lymphocytic cells or the other cell type. Granulocytes or myeloid. Yeah, so you've got the myeloid line and the lymphocytic line and the lymphocytic or lymphoblast line will turn into the T and B cells. It also turns into the NK cells actually. Yep. So the B cells then remain in the bone marrow where they go through their...

like this is military training, to kind of try to make sure they are not too aggressive, so not too over the top, but not too lazy. So they kind of mature them in that way. Then they usually go to, commonly, they'd probably go to lymphoma.

Yeah. Where they will be waiting for the encounter with a pathogen. Yes. Okay. The B cells. The B cells. All right. Now, but at this, it's important to note at this point, they are what we call naive, which they haven't been kind of precisely adapted to. Yes. Now, when they do encounter something that is pathogenic, they need to be selected for. So each pathogen,

This is, again, broad brush, but generally speaking, we'd say a B cell has a specific type of antibody that it can produce. Yep. You would say the body has the potential to make millions of different types of antibodies that is specific for a specific type of antigen. Yep. Right? Now, it needs to be selected for. Once it's selected for, once it's saying, hey, you're the B cell we need, all that would really do is turn it from a knife into a...

of producing antibodies and these antibodies are just proteins that lock on to the antigen of a microorganism, let's say. Yeah, and generally speaking, the antibodies, like you said, when they lock on, they can do a process called opsonisation, which is sort of just like suffocating it, right, and surrounding it to stop it from having, you know, that means the antigen itself or the pathogen can't actually bind to anything and wreak its havoc, right? Yeah.

But also in that process of opsonization, it calls upon the T cells. So let's talk a bit about these T cells. Yeah, yeah. Okay. So the only thing I'll just say with the final thing with B cells is once they've done all their production of antibodies, they can turn into memory cells. So they are still there. They'll just hang around and they'll be there in case another encounter with that same microorganism comes about. Yep. Now T cells, they have...

Further divisions, T because they mature in the thymus, which is a gland. Which you and I probably don't really have anymore. Just above your heart, behind your sternum.

That starts to- Behind your sternum? Behind, yep. That starts in the medial, we'll just say it's in the medial sternum. It starts to atrophy each decade beyond the 20s, let's say. Yeah, so if you're a, let's say a medical student or even a lot of health students will do dissections, right? If you have an older individual- It's hard to find. And I said find the thymus, you probably won't be able to find it.

And that's part of the reason for the immune senescence as we get older is because we have atrophy of the thymus, our ability to produce cancer.

different T cells is very difficult. Yeah. Now, what do the T cells do? So T cells can be broken into three types. You can have the killer T cells, which are like natural killer cells, but they're a little bit more adaptive. You have the T helper cells, which are the coordinators of the overall immune system. And then you have the regulatory T cells. Yeah.

Okay, so we've got our T and B cells. They are adaptive. They can recognise certain targets. They can maintain a memory of these targets. And they're very important in obviously maintaining health and wellbeing. When we think about vaccines, for example, they're leveraging this adaptive arm of the immune system because...

you're exposing the T and B cells to an antigen, a little flag on the outside surface of the pathogen, without generally exposing the individual to the pathogen itself. Yeah, so that gives an important point. This speaks to what we call immunity. Okay, so immunity is something that the immune system hopefully generates or creates, and that's where you're free from disease.

Okay? Now, when you are free from disease, that means you're not going to have the infection causing damage to your body. Now, when we look at immunity, immunity can occur through a different type of mechanism. You can get it...

From an active process. Yep. And that can be from the infection or it can be from a vaccine. Yep. Or you can get it passively. You can get passive immunity. So sometimes you can get that from the mother. If you're an infant, you can get that through the placenta while you're still an embryo or you can get it through breast milk to a lesser degree. Yeah. But that is still immunity. So you still have the potential to fight off or get rid of that infection through different means. And,

And so just to clarify, the passive immunity is you're actually directly receiving the antibodies that have already been generated. That's right. Active immunity. Without your immune system doing anything. And yes, the active immunity is you're generating it.

One is not necessarily better than the other. They're both very important processes. But importantly, when you think about vaccines, for example, when you are exposed to that antigen, that flag on the surface, without being exposed to the active, you know, the damage-causing agent...

You were developing the same immune response that you would without the disease. Now, an argument could obviously be made that it is probably not as good of an immune response. And that probably is true. And that's probably true. And the reason why is because if you're exposed to the entire pathogen, you're going to be exposed to multiple antigens on its surface and you develop a range of immune responses to it.

However, the worst way to develop immunity for a disease is by getting the disease because it's stupid to say, oh, the bacteria

The best way to avoid measles is to get it. That's the dumbest thing I've ever heard. So getting something like the measles vaccine is a very good way of not ever getting measles. And the vaccine itself is enough, is sufficient to not get the disease, which is measles. Some vaccines aren't necessarily sufficient to avoid getting the disease. For some people it will be, but for others not. So the COVID vaccine, for example...

is a really good vaccine at reducing the severity of the illness for us because we are exposed to some degree or some variants of that virus, which means that when we contract it through, you know, you sneezing into my mouth, you pig, that my body's already recognized it. So I don't have that lag phase of having to develop the white blood cells, the T and B cells.

I will be able to defend it and attack it straight away. But it's not great enough that I don't necessarily get any symptoms, but probably reduces very confidently my symptoms by a significant amount. However, in the case of measles, the vaccine is good enough to not let me get the disease measles, if that makes sense. So not all vaccines are created equal in that sense. And it's also important to note here that when you... Is that... Are you...

happy and comfortable with that statement that I made, with those statements? Yeah, broadly, yes. It is true. But it's also important to note here, because this is where we get some opposition, not necessarily from our listeners, but from the broader public, that with any medical intervention we do, there are risks. So there is...

quite distinct possibility but by having a vaccine there can be side effects for some individuals. Now particularly because we are stimulated in the immune system so whenever we stimulate the immune system whether it's by a vaccine or an infection it can cause whole body changes. Yeah. And some of the issues that we have and this is what

I was going to add on here is when we look at the life cycle of an infection, we generally see we have like an incubation phase, we have a prodromal phase, we have the active phase where all the main symptoms come about, and then we have the phase where we go into convalescence and it goes back to normal. But there are a lot, I would say a lot, there's a lot of infections that we can get that can then lead on to chronic disease. And so some examples could be,

say hepatitis, it's a virus that you may clear, but what it then causes is chronic inflammation to your liver. Live from the internet's red carpet, it's Vrbo's 2025 Vacation Rentals of the Year. Selected from over 2 million private vacation rentals, this year's list features the best of Vrbo. And with weekly discounts on select stays, they might be more affordable than you think. See the list at Vrbo.com and make it a Vrbo. And then chronic inflammation in the liver then causes, because when the liver's chronically inflamed...

It lays down collagen and we get cirrhosis of the liver. So as an outcome of hepatitis, particularly say B, actually all of them will probably have this as well, but this is why we get a vaccine for B, is because maybe not so concerned about the virus per se, but it's effect now on the liver. You don't want to have cirrhosis of the liver because now your liver won't work. We have certain viruses that can cause cancer. So HPV virus, this is why we're vaccinated because it's not so much we're concerned by that, but...

but it then can lead to cancer. That's right. So there are COVID, for instance. Yeah. There was a significant amount of population that developed long COVID, which is a long protracted, drawn out disorder, which we can avoid if we go with use of vaccines. So same with your example as measles. For a lot of individuals, they will get the virus, they'll get the skin eruptions, they'll get those changes and they'll be fine. But why?

1% of babies will die from it. Yeah. 1% will get brain injury. 1% will lose their hearing. So these are complications you don't really want to take your chance with. No. You'd rather prevent it with a vaccine. And you could think, oh, 1 in 100. That's fine. But when you've got millions of babies, that's thousands of deaths, right? Thousands. But it always –

puzzles me that when people look at that as going, oh, well, that's worth risking. It's not ever. But then you translate it into some other real world example. If there was a bridge that one in 100 cars would plummet into the... No one ever would drive over that bridge. No, that's right. But when it comes to this, for some reason, people think that's a risk that's worth taking. Because our brains are... Human brains are very strange when it comes to risk taking because the way they think is that...

By taking an action, if there's a one in 100 risk of taking an action, they won't take the action. So like the bridge thing, right? They'll go, oh, there's a one in, it's easy. I just won't take the action and I negate the risk. But if they say not doing something, there's a one in 100 risk. Well, I'm already not doing something, right? And if I did something, I might get sick from the vaccine. Then they're like, well, I'm not going to take an active dose

I'm not going to take an action for a risk when I could take no action and possibly something happens because it's not my fault because I didn't take an action, you know? So it happened to me as opposed to me initiating it. Yeah. If that makes sense. Anyway, that is a hell of a sidetrack. We haven't even spoken about exercise. Let's talk about exercise 40 minutes in. Sorry listeners. So we've set the scene with both innate and adaptive and this is important because this is where exercise fit in. So,

We've probably known for a long time, at least anecdotally, that people who are more fit, they may... Why are you looking at me, Matt? More actively... Active. Active. They have maybe less of an impact with illness, particularly from infections. Now, a lot of the discussion we're going to have today around...

infectious diseases is a lot of the research has been looked at, at upper respiratory tract infections, which like common cold, for instance. Why, why would we look at that? Well, it's the most infectious type of infections. Yeah. You're really good at using redundant words today, aren't you? Let's just say the same thing twice. Communicable? Yes. Communicating communicable diseases. That's right. So they're the infections that we're likely to pass on to each other relatively easily.

And relatively common for people that exercise. Yeah. So, and also the fact that

I think it's pretty commonplace now that when we talk about benefits of exercise through health broadly, this series will talk about – I think every episode will probably touch upon the way that exercise can benefit various aspects of the body because we're going to go through the organ systems and how exercise affects them. So obviously we could very easily talk right now about the benefits of exercise broadly to health. It feels like it needs a specific arm of –

specialisation, this exercise in the immune system. Yeah. If I were to make a name for it, I would call it exercise immunology. Brilliant. It already exists. What?

Yeah. Say what? So if you are somebody that studies the effect of exercise, psychological and environmental influences on the immune system, well, well, well, you are an exercise immunologist. Go climb that tree. Now, what we're going to take a look at. Now, before Matt, you know, I'm so sorry for talking while Matt interrupted, but what I was saying before was that exercise,

We could talk about the broad effects that exercise has on health and the fact that one of the best things you could possibly do for your health and longevity is moderate intensity exercise, right, over time.

The end. But it's, it's just that that's just the fact, but, and we're going to talk about that in regards to each specific organ system as we move through. But what we're going to talk about today is the acute effects, right? Not good looking, but the short term effects that exercise can have on the immune system. And I think that's important because that's one way that we can very clearly measure changes in the immune system. So first thing I want to say is, um,

We should talk about the fact that exercise in the acute term, short term, has both a positive and negative effect on the risk of developing an infection. And like you said, let's frame it in the upper respiratory tract infection area because that's where a lot of the research has been performed.

There is a J-shaped curve. Like a tick, like a Nike tick. Yeah, like a Nike tick. This episode is not sponsored by Nike. However, the money would be good. Nike? I've been into. Want to sponsor us? I've been to requests. Yes. If you do sponsor us, we'll start calling it a Nike tick-shaped curve as opposed to a J-shaped curve. So this J-shaped curve effectively –

It talks about the fact that if you've got on the Y-axis your risk of infection and on the X-axis your exercise... The exercise intensity. Thanks again, Matt. Exercise intensity. As you increase your exercise intensity, so in the early phases, you know, you have effectively from low intensity, you've got a relative degree of protection from infection. But as you start to do moderate intensity exercise...

you'd now become reduced in your risk of getting an infection. And then when you perform high-intensity exercise, it jumps back up again and you've got an increased risk of infection. So would that, at the high-intensity level, would that then be a higher risk than...

Doing nothing? Yes. Okay. Correct. So high-intensity exercise increases your risk of developing an infection, in this instance upper respiratory tract infection, more so than being sedentary. Right. Does this go back to the principle of hormesis? Well, yeah, it does because...

Remind us what that is again. So your body will adapt to stresses as long as that stressor isn't so significant that it pushes your body outside of homeostasis to a degree that it can't maintain normality again. So generally speaking, you know, to put this into a simple context, I go into the gym, I lift some weights, do some bicep curls, my biceps, the muscles go, holy crap,

I'm not liking this. This is stretching me. This is hurting me. I'm going to ensure that I get bigger and stronger. So next time I'm exposed to this stressor, i.e. arm curls, I can withstand the stress. And that adaption is that process of hormesis, right? It's basically you're adapting to a stressor and it's physiologically beneficial, anatomically physiologically beneficial.

However, we know that I could go into the gym and I could do three hours of biceps curls, right? Which you do actually. Sometimes I do. But what happens is my biceps, same thing, freak out, try and release all the appropriate chemicals to grow and develop. But I'm stressing the biceps out so much that I harm the tissue and it can't grow and develop and,

adapt in a way that's beneficial. So this can happen through high intensity exercise. So if you're an elite athlete and you're training so much, you can actually increase your risk of infection. And the reason why is because it can suppress certain immune cells. We'll get to that. Yes. Let's first talk about the benefits. So the summary just of what you spoke about with the J curve is really the Goldilocks zone.

Yes, yes, very good. Yes, the porridge is just right here. Like it. Yeah. Move on. Okay. So regular moderate intensity exercise.

has shown to result in individuals catching fewer colds, right, or upper respiratory tract infections. It can reduce the risk of upper respiratory tract infections from between 18% to 67%. Now, when we talk about regular moderate intensity exercise, we're referring to 20 to 40 minutes of moderate intensity, which is about 40% to 60%, your VO2 max,

Per day. So this is aerobic exercise. We're not talking about moderate intensity resistance training because the evidence isn't as strong here. But it's still there. We'll come to that. Yeah. But it's the aerobic training. Is this across all age groups? Yes, it is. But the older you get, the less effective this is.

Still beneficial. But you would say that for older individuals having this regular exercise regime... It's grossly beneficial. Yeah. Yes, yes, yes, yes. But its potency is probably reduced due to... A number of factors. Yeah. One of them is simply your physiological reserve. The fact that everything just doesn't function as well the older that you get. Now...

When you do this exercise, this moderate intensity exercise, some research has shown that your NK cells go up.

Right. So remind us again, NK cells did what broadly? Natural killers. So what did they do? Kill things. Okay. That makes sense. Your neutrophils go up. Why is that important? They're the first responders. Brilliant. And your antibodies can go up as well. They're the ones that just go around and lock onto antigens that are deemed, well, just say antigens. So this is both urinate and adaptive immune system. So important key regulatory cells of your immune system from both adaptive and innate go up and

During exercise. Do we know why? Well, a couple of reasons. So a couple of things change. You're the –

Your metabolism changes, right? So we know, we've spoken in previous episodes, that your muscle will switch metabolic products or sorry, metabolic sources during certain types of exercise. So we- Has different preferences, right? Preferences. And so do your immune cells. So you can either preference glycolysis, so glycolytic processes or oxidative phosphorylation based processes.

This shift in the way it undergoes metabolism can change its profile in regards to how many oxidative stresses it produces, but also antioxidants it produces, and can result in either a negative or beneficial effect. So generally speaking, the fact that it is changing its metabolic sources results in a more protective environment for immune cells. So it's better for the immune cells of the body.

So if the immune cells, so the white blood cells specifically here, are going down more oxidative phosphorylation process, so it's now producing a higher amount of ATP internally, that then just makes it a more energetic state for it, which then improves its ability to perform its own immune functions, but also for migration as well. It can move around quicker. So it's more like it's on...

Like it's on Red Bull almost. Yes. And we'll talk a little bit about that in a second. Another reason why we tend to get this immune benefit is that it increases your psychological well-being exercise, particularly in moderate intensity over time. And we know that a poor psychological state or a state of stress can release cortisol. We spoke about cortisol in previous episodes. It is an important regulatory hormone for the metabolic sources that we use. It tends to mobilize.

free fatty acids and glucose, predominantly glucose into the bloodstream, which is a good thing, right? In short term. In the short term, precisely. But long term, it's like that inflammation in a way, you know, you don't want it. So long term, this is why the high intensity exercise or long duration exercise can be detrimental, is that too much cortisol in the system can actually impede the way, because it's a steroid hormone, it changes the transcription of genes, turns it on or off.

It does this so much so to our immune cells. It can change how T cells are transcribed in other cells and suppresses the immune system long term. Yeah, particularly the cytokines. So it's going to...

Have an impact on the way the white blood cells communicate to each other, which dampen it down and therefore make it less efficient. Exactly. So exercise can alter the number of the circulating immune cells, but also the activity of the circulating immune cells. So just to go back to the point that you highlighted about making those cells more energetic, right?

If I said to you exercise can increase the number of these, let's say, white blood cells, which can – so again, evidence has shown that leukocytes and lymphocytes can increase between 50% to 400%. So circulating leukocytes and lymphocytes increase by that much during exercise, moderate intensity exercise.

Is the body making these white blood cells or are they already present and we're just sort of recruiting them from existing regions? The latter. Right. So it's almost like, you know, how I like my analogies. Yeah.

It's like we haven't had a rain for a long time and all the dirt and leaves are all kind of accumulating on stormwater drains and then we get a big flush and it washes them all out. So it's a bit like that. These immune cells, natural killer cells, neutrophils, antibodies are all clustered in

on the sides of blood vessels. They're all kind of marginated there. Particularly the neutrophils. And then as soon as you increase your exercise, we know that it boosts your amount of blood perfusion through the body. Yeah. Huge amounts, like a hundredfold. So it just blasts and flushes all these cells

being atrochila, neutrophils, antibodies throughout the circulation. That's called demargination. And so now we're having just more abundance. So instead of them accumulating in one area, like for instance, they seem to be overrepresented in the capillaries of the lung and in the...

And then once we get a huge bounce of exercise, which would also go with certain hormones like adrenaline and cortisol, that also changes the profile of the cardiovascular system, which then causes a better distribution of these cells. So effectively, the increase in circulating numbers of these cells that we've spoken about happens because the preeclampsia,

and the circulating hormones trigger them to basically pop off from holding onto the sides of being stuck to these endothelial cells of the vascular tissue. They pop off and now they're floating through the bloodstream. All right, so that's important. It also increases their activity as well. Now, that's important because increasing their activity means that they can, and like you said, because you're increasing the energy that they're producing but also utilizing as well.

Now, an important point here is that a lot of this effect that we see is the immune system is boosting during exercise and then often can drop back down to normal after exercise. And this is really important because it's individuals. So if you were to compare athletes with non-athletes,

At rest, there's no difference in their immune function. So it's not like if an athlete at rest has a better immune system than a non-athlete at rest. But...

When they exercise, if it's moderate intensity exercise, the immune system does boost. I hate using that term, but the number and activity of the immune cells does go up. The efficiency. The efficiency. But also after exercise, it drops back down to normal. However, there's even some cells that after exercise drop down below their normal levels. And these cells include the natural killer cells and the T lymphocytes, so the T cells. And the reason why is that it seems to be that...

Once exercise is finished, we know that we've put a lot of stress on the muscles. And so the muscles are going to have some degree of inflammation because some degree of damage would have been caused and certain chemicals are being released. And so the T cells tend to jump out of the bloodstream into the tissue. That's called extravasation. So they jump out into the tissue where they act as sentinels. They walk around making sure everything's okay. Nothing I need to kill off here. Everything all good.

but that tends to be the functional T cells. So the more immature T cells remain in the bloodstream, hence why the numbers drop in the blood plasma, but also through really high intensity exercise, your immune system can actually be suppressed, right? So you're at an increased risk of infection after exercise, again, particularly with high intensity exercise for a certain window.

So for example, marathon runners were shown to have decreased. So this is in a two to nine hour window after the marathon, right? Right. So marathon, if you are an elite athlete, you're doing this for two hours? Two and a half hours. So anything over high intensity over 90 minutes? Yep.

falls into this category? Yes. So for a window of two to nine hours after that training, there's this open window. So you've got a decrease in natural killer cells, T cells and B cells, a decrease in their activity, a decrease in nasal neutrophil phagocytosis. What's that mean?

Well, neutrophils we've already covered, that's a type of white blood cell, nasal phagocytosis. So I'm guessing what this means is within your nasal mucosa, you have less white blood cells to be doing cleaning up activities. And if you think about it, if you've got less activity of white blood cells cleaning up in the nasal cavity, but you're breathing a lot more due to exercise, you're exposing your nasal cavity to far more pathogens, right? Yes.

So those two things in combination increase your risk of infection. You also have a decrease in salivary immunoglobulin A. So what's this mean? IgA or immunoglobulin A. So that just is a type of antibody. So when we look at antibodies, as I said, we've got millions and millions and millions of different antibodies in the body, but they generally classed into five different categories or classes and that's based on its chemical characteristics. Okay.

And IgA is just one type of those. Yeah. And it also increases your cytokines, both pro and anti-inflammatory. So what this does is it creates a window in which you've got a depression in your overall immune function. Again, this is far more predominant in high intensity or long duration aerobic exercise. All right. Now...

Matthew, I think it's important to let everyone know that it's not just the exercise that causes a suppression in the immune system for athletes or for those doing high-intensity, long-duration exercise. There's other factors. So yes, it's the exercise. But what else? Do you have any other factors here? This is for athletes? This is for athletes. To increase their susceptibility to infection. So yeah, the exercise because of all those things we just mentioned. What else?

Well, I guess it's all the things that go around that as an athlete. So particularly if you're getting to the point of competition, you're probably going to be starting to be under stress. Yes. Mental stress, emotional stress. All right. So what's that mean? And we know that stress –

We'll call it psychological stress. It has an effect on the cortisol or the stressor hormones. And stressor hormones are fine in the acute, but when they are chronic, they can then suppress the immune system. Yeah, so if you're stressing about an event that's in a week or two, then you're not having an acute release due to an acute bout of exercise. You're having a chronic release, simmering, bubbling away over time, suppressing those immune cells.

It can also be due to just increased exposure to the pathogens. So we said through that breathing in and out, you're just breathing in more and more pathogens, but also... Well, if you go into competition, let's say the Olympics as an example, you are going to a particular location with thousands of other people. Athlete village. Yeah. You are traveling there. So you've probably gone on a plane, sat on there for 10 hours in a confined space. Yeah.

with recycled air. So that increases likelihood and you're just being exposed to a whole lot of pathogens that you wouldn't normally...

Been exposed to. Inadequate diet. So while athletes generally eat very well and balanced, it may not meet the caloric demands that's required of them. So that can be an issue. Lack of sleep as well is another one. So evidence shows that athletes don't sleep as much as they probably need to for their recovery. Or the quality, right? And the quality is different too. Correct. Correct.

All right. Now, before we go into the final point, which everyone's been waiting for, should you exercise with a cold? What about exercising in environmental extremes? So does this affect your immune system if I train in the heat or if I train in the cold or if I'm training on top of Machu Picchu? Are there any differences? Well, if we look at heat and cold, broadly you wouldn't say a huge amount. Okay. You would say probably hot is pretty much the same as cold.

ambient temperatures elsewhere. Cold in the short term seems to be a little bit immune stimulating. Not a huge amount, but there is a degree of, I guess you could say, benefit in exercising in a colder environment. But maybe if that's prolonged, it may not be that same stimulating effect. Now, there's a couple of caveats with those two points. Starting with heat. Heat is obviously another stressor on the body.

So you've got exercise, which is a stressor, and you've got heat, which is a stressor, particularly if heat's in conjunction with humidity. That then makes it more challenging for your body to thermoregulate. So if you're doing those together, particularly if it's pushing your body's homeostatic mechanism towards a deranged region,

So it's going to a temperature that's maybe now detrimental. It's so hot that you can't sweat enough to relieve the temperature. That's right. All the sweat is ineffective because with humidity, we know that. So that then is going to have an effect on the body and the immune system, which could become a little bit detrimental. So you have to keep that into consideration. But you're probably saying the acute setting with a hotter temperature, it's not going to have a profound difference or negativity. All right, cold. Cold, same thing.

seems to have a little bit of stimulated in the short term, probably again through the stress hormones making the cells more active, more efficient, more distributed, particularly in areas that may be exposed to the cold. Now, another caveat here is if you are

exposed to real extreme cold... Below zero. You can now... Not Kelvin. You now have the potential of causing injury to your upper respiratory tract because remember, the respiratory tract is there also as air conditioning. Okay? It wants to have air entering your alveoli...

at a temperature of 37 degrees and being humid. Now, if you're bombarding it with zero temperature that's dry, that can cause injury to your upper respiratory tract or dry it out, then that impacts the innate immune response, making it a little bit more vulnerable. All right. But again, broad brush, you would say not a huge effect either,

or negativity. Yeah, very true. Yeah, the evidence shows that training in those two environments do not really significantly alter your immune function. But what about high altitude training? So this is where you'd probably go. So you said Machu Picchu, which is probably 4,000 metres above sea level. Yeah. So anything above 3,000 metres, which is 6,000 feet, you would start to see changes physiologically because you've got less activity

Partial pressure of oxygen. Okay. So it's just the access to less oxygen. That's right. And again, this is a stressor. So your body needs to counter this by changing its physiology. At the same time, it's exercising. So another stressor, compounded effect. Now, if you are resulting in profound hypoxia...

that's going to have a change on your immune system. Now, if that's, again, we're going to release stress hormones, so probably in the short term we might have some more beneficial or immune stimulating effects where the immune cells are becoming a little bit more efficient and more active and more distributed. But if this is prolonged, especially if you haven't, what's a term we used earlier on? Not adapted, but you are...

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You've changed to that local environment without giving your body that time to adjust. Yes, yes, yes. But...

Yeah, it's not adapted, but I know what you mean. So therefore that could cause probably some immune suppression. But broadly speaking, again, if you're – so if you're training in high-altitude environments –

you're not going, I can't breathe, but I'm still pushing through. Same with the heat. You're not going, I'm running through the desert in Dubai, but I'm going to push through or I'm running through the Arctic. I'm going to push through. If you're just training reasonably, water intensity exercise within cold environments, hot environments, or even high altitude, broadly speaking, would you agree that the evidence shows that training in these environments really don't significantly alter your immune function? Yeah.

And if you were to do any of them in the extreme, the last thing I'd be worried about is the function on the immune system. I'd be worried about dehydration in the heat. I'd be worried about... Or heat stress. Or heat stress. I'd be worried about hypothermia or damage to my mucosal tissue in the cold. And in the high altitude, I'd be worried about hypoxia and cerebral edema in the high altitude. And the other things that go with altitude...

I don't like your altitude. Because you are having other physiological changes to that shift. Yeah. You are, other things are changing. A bit like what you said with elite athletes. It's not just the exercise. It's the-

The diet or the nutrition, it's the sleep, it's the stress. It's a bit like that attitude as well. You're trying to regulate your acid base so your kidneys are doing things differently, your sleep quality has changed because again things are shifting. The way your metabolism is coordinated has changed. So all these other side effects are going to have an impact on your overall homeostasis. Yeah.

All right, Matt, we're down to the last point, the one that people have been listening to us for one hour and six minutes for, to find the answer to, should you exercise with a head cold? Now, what goes the research? Should we exercise when we're sick? Well, again, this is a boring answer. Oh, here we go. But it comes down to listen to your body and it's common sense, really. Okay, but there's more to it than that.

So, all right, if I'm going to give you an example, I have a snotty nose, I'm nasally congested, got a bit of a sore throat. Can I train?

Yeah, the rule of thumb here is if the symptoms are above your neck, it's probably okay. If they're below your neck, give yourself a break. So if I've got chesty cough or even any respiratory issues. Or systemic effects like fever, myalgia, those kind of things. Muscle soreness, fever, even just overall fatigue. Your body's telling you something. Gastrointestinal, yep.

Well, the last thing you want to do is run with that. Your body's saying time for rest. Yes. If you've got... There's a reason for that one, right? Yeah. So why do you think we've evolved when we're sick to feel tired, to feel lethargic, to feel like I don't really want to eat, to feel achy? Because it's saying, Matt, stop. Yeah. Stop. Because...

I need to funnel all of our resources to the immune system... Correct. ...so that we can respond to and correct the homeostatic imbalance that's occurring here due to some invading pathogen, viral, bacterial, injury, whatever it might be. So, again, listening to your body is a good way. I really, really don't like it when people... Have

Have you heard of, oh, now I'm blanking on his name. There is a, Joe Rogan made him famous, a runner, ultra marathons. I don't know, David Goggins. You've heard of David Goggins before. Okay. Ex-soldier. You know, I think he's now a firefighter. You know, obviously an extreme fighter.

Individual. Motivated, dedicated. Strong mental strength. Amazing. Done so many amazing things. But part of his fortitude, a byproduct of that is that even when he's sick, he'll train. And even if his body is sore, he'll train. And I know that a lot of that is a mental game for him just to say I can do anything and get through anything.

But, you know, I really don't like that because the message it sends is you should and, you know, if you can, you should. And I don't think that's the case because it can very much delay recovery, can very much make you go backwards in your training and health and you should listen to it. But again, head cold, above the neck, fine. Don't go insane. But below the neck…

Last thing you want to do is go for a marathon length run with a chest infection, right? Last thing you want to do is a CrossFit workout when you've got a fever. Because what did we speak about weeks ago when we spoke about what happens to the body cardiovascularly at least when we exercise like –

From a cardiac output point of view. The demand goes up in... Yeah, so normally a skeletal muscle gets, what did you say, 10%, 15%, 12% of cardiac output. Yeah. And then once you're exercising, fairly high intensity. What percentage of blood flow now are we talking? Well, it goes from around about a litre a minute to up to 20 litres a minute of blood going through the muscles. So a hundredfold increase of...

blood cardiac output to those structures. At least 20 fold. So that then means, because cardiac, not only does the percentage change, but also the amount of cardiac output you're now generating. So that's now telling you that the primary demand now is going to your muscles and it's

In the case of fighting an infection, you want more of the resources to be going to your immune system. And as we know, after that training, your immune cells go down. And also the stressor hormones, cortisol being one, if you are extending, protracting, lengthening this high intensity output, that's going to be producing cortisol at high levels, which is an immunosuppressant. Yeah. So we do know clearly that if you were to take

a cortisol derivative like prednisone, so this would be systemic, over drawn out periods of time, one side effect of that is extreme immune suppression, which puts you in a vulnerability of getting sick. So if you're sick and you want to train, be reasonable. Yeah, and it's not us for a second trying to say don't. It's just saying, you know, you've got to be cautious with it. That's all. Yeah, absolutely. Absolutely.

Anything else you'd like to add before we tie a nice bow on the end of this? The bow could be this. So there was a study that was done reasonably short after COVID. It's not really wrapped up and forgotten about. Okay, yeah. Looking at approximately 50,000 individuals that had a very strong correlation that individuals that were more active –

So performed exercise more frequently, had lower rates of hospitalisation, ICU admission and death from COVID. And from a multitude of reasons that we spoke about,

improved antibody mobilization, so it's moving it around the body, enhanced, even the enhanced vaccine results or responses. And again, this goes to we've put the antigen in, we've brought more cells to the area, we've made the immune system more efficient, but then we continually circulate it more effectively because we're exercising, having a better immune

more robust response and it seemed that the VO2 max correlated to better outcomes. I'm sure to a point that it becomes detrimental if you are exercising at 80%. Yeah, there'd also be a J curve there, I'm sure. But, you know, I think one, that's very important. Obviously, health, physical exercise is protective for disease. You know, we know that. But it's important to say that, you know,

It might be protective, but it doesn't definitively protect you. Meaning that just because you exercise moderately 20 to 40 minutes, 40 to 60% of your VO2 max every single day, you eat well, you sleep well, you're putting yourself in the best situation for health and longevity. But it doesn't make you immune from, mind the pun, from...

Health effects, right? It doesn't make you, it doesn't mean that, oh, I've got a virus, I've got a head cold, or I've got COVID, I must have done something wrong. No, these viruses, for example, have evolved to jump into your system and attack you. It's just that the protective effects mean, again, decreased risk of hospitalization and severity of symptoms.

But again, there will be people who are extremely fit and healthy and need to be hospitalized or even die from these diseases. So again, at a population level, it's protective. At an individual level, the argument is you are in the best place you can be

but it doesn't protect you fully from any of these things, right? Exercise. So that's just a caveat for people who might want to see the world in black and white and go, well, if it doesn't protect me 100%, I'm not doing it. And that's in many things, including vaccines, right? There's obviously arguments. I'm not jumping into the vaccine discussion again, but there's obviously arguments out there saying that, well, if the vaccine doesn't protect me. Why bother? Why bother? Well, then don't do any exercise either. Right?

Right? Don't eat well. Don't sleep well. Don't do all these other things well. Don't you want to put yourself in the best situation possible? I do. Or probability. I want to exercise. I want to not drink alcohol. I want to sleep well. I want to eat well. I want to get vaccinated when I can at the most appropriate times. Like...

All these things are putting me in the best place possible for health and longevity. I think you said it, not in this podcast, but a previous one, that it really depends on what your objective measure here is. Is your outcome longevity? Is your outcome having performance? Is your outcome being just more energy? I mean, so depending on what you want here,

certain things that you need to do are going to be different. So if you're wanting to live longer, there's going to be a number of things that you have no control over. Yeah. You know, your genetics, certain things that have already happened, you know, you're predisposed to. Yeah. But you can. And another example here with exercise.

For instance, there's push to suggest that both muscle and even adipose tissue is endocrine tissue because they have an effect profoundly in the body and they produce their own cytokines which modulate the immune system in their own way. And so by having active muscles...

exercising all the time, it's going to modulate, play away with the immune system, but also fat cells and it being more sedentary, it's going to have more pro-inflammatory. So by exercising, that's going to have health benefits. But then what's the Goldilocks zone that we spoke about? That's going to be difficult to measure person to person. You have to kind of find what suits you, what's for one, isn't going to be for the other. So we're again, broad brushes here. But I

It comes down to a very boring, monotonous answer being... Moderate. We need to sleep. We need to eat well. We need to move. Yeah. If you do those three things generally well, you're doing the best thing you can for your body for health and longevity. Yeah. And look, it's a really good place to end the podcast, but I'm not going to because I've got more to say.

This is a gripe that I have and I think you probably have it as well but you're probably not as vocal as I am about it in that there are podcasts out there that go for four hours which talk about –

the minutiae and details of how long you should hop in an ice bath for or tweaking this very small little variable for your benefit. But at the end of the day, the biggest health changes occur through maintaining and being regular with moderate intensity exercise, good sleep, balanced diet,

Those three things are insanely important and that a lot of people aren't doing those. And you could say mental health as well. Definitively mental health, yes. You're right, we shouldn't be throwing mental health out because mental health is one in which you can benefit it through exposure through community. I mean that's a huge one. Those four things, seeing friends, eating a good balanced diet, nothing extreme there,

Sleeping your eight hours of quality, a round issue. Obviously, you know, it's not- What suits you. Yes, yes, yes. And regular moderate intensity exercise. I mean, those four things probably consist, and I'm just making a number up here, but ballpark, that's probably-

95% to 99% of your health and longevity of the modifiable variables, I'm saying, are sitting there. And then all those other things about like infrared saunas and ice baths and taking particular supplements and so forth, you're tweaking the point something of a percentage there, right? Which is negligible, negligible long-term. And people are spending –

time and energy and stress and money on these things when they're not even exercising consistently sleeping well eating well and hanging out with their friends just do those things well and stop stressing about your life and stressing about those all individual things and worrying about oh when i hop into the ice bath it needs to be this particular temperature i need to go in for this long i can't put this particular body part into it blah blah blah but i mean

They're stressing about an ice bath. That blows my mind. It blows my mind. And so I know that this conversation is derailed, but it's talking about, you know, the immune system and so forth. And I think it is important to discuss all those particular points. But saying that, I think if those add-ons add up,

you know, a qualitative benefit to your life. Like you look forward to it, you find it as a, that feeds into mental health, I think. I totally agree. Where you just have these, oh, I'm really looking forward to my ice bath or I'm really looking forward to whatever and that adds value to your life. But as you said, when it becomes a prescriptive focus and I have to do it to this precise level in this perfect amount, then it becomes, I think, a mental stress which then does a detriment. Yeah.

That is a great point, yes. I mean if people are doing this because they love maintaining a routine and it provides them with some psychological benefit, wonderful. As long as it's not a detrimental – the psychological benefit is not negated by a detrimental harm, right? Absolutely. I think that's great. And I have cold showers and I don't do it for any physiological benefit. I do it because when I'm in the cold –

Showers are great times for your mind to wander. There's nothing wrong with that. But I'm always thinking. That's just me. That's how I am. We've spoken about my ADHD and that my thinking can often be of detriment to me. I like cold showers as cold as they could possibly be because I can't think about anything else but surviving the shower, right? Yeah.

That's good for me because I finish the shower and it's sort of a mindfulness meditative thing for me. And like a grounding effect as well, right? You're really in the moment. You're really in the moment. And someone could argue and go, there's no physiological benefit for that so I don't know why you're doing it. But you made a great point. It's not all about the physiological and sometimes the psychological. So I can see to that point, absolutely right. Right.

But there's so much we can talk about with this and we will. We'll touch upon all these additional points when we go through the various organ systems of the body, but we might leave it there. I think we've highlighted well enough. I think so. That a good moderate amount of exercise has a good benefit on your immune system. So as best you can, try to keep it common. Keep going. Often. Often. That's what we're looking for. And –

Yeah, that's a good take-home point, I think. Agreed. If you would like to provide us feedback, mostly the positive, you can send it to us.

admin at drmattdermike.com.au. You can follow us on social media at drmiketodorovic, that's at D-R-M-I-K-E-T-O-D-O-R-O-V-I-C or search drmiketodorovic on all social media platforms. Matt doesn't have social media, so he refers to me to do all the hard work. You can follow us on YouTube and watch our videos.

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Look after yourselves. We love you all. Speak soon.

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