Exercise Physiology | Control of the Internal Environment (Part 1)
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Welcome everybody to another episode of Dr. Matt and Dr. Mike's Medical Podcast. I'm your host, Dr. Mike Todorovich, and I'm joined by my co-host who's walking through the door now. Maddie, what are you doing? Do you want me like?

I love you. Oh, am I standing still? What are you doing, dude? I love you, Jewel. Wait, is that a Jewel song? Jewel, yes. Jewel, what song was that?

Homeostasis. What? That's why I enjoy that song. I don't remember her singing a song called Homeostasis. Are you standing still? Oh, very good. Which is obviously the definition of homeostasis. Because obviously that's what she was thinking. She was talking about blood pressure and how blood pressure goes up when you're in love. Quick question. How do you know that song? Well...

If you want the truth of it. No, I wanted a lie. I wanted a blatant, obvious lie. That takes me back to my time in America. Okay. Where it was playing, I think, every morning on the radio on our trip to work. What was your work? Ski field. Oh, okay. And it stuck my brain forever. Wow. So if you're listening, Jewel, thank you. And I love you.

Homeostasis, yes. Yeah, we're going to talk about not just homeostasis in regards to it generally within medicine, but probably a little bit more specifically within exercise and exercise physiology. Matt and I have decided to do a series, right?

Still doing our medical podcast episodes, but you'll find that we are doing a series of episodes on exercise, performance, and its application in health and fitness. To EPs. Yeah, not just exercise. Because they're our forgotten audience, I feel. Yeah, probably not even an existing audience, but this is just for anyone interested in health and fitness, right? We're going to be talking about physiology of health and fitness. Physios, right?

This is going to be beneficial for you. Yeah, stop listing groups because it's going to... People are going to go, oh, I'm not one of those. I like pigeonholing people. Stop it. This is for everybody. This is for everybody. And we need to begin with homeostasis because the concept of homeostasis is extremely important, not just for medicine, but for health and fitness. Do you agree? Yep. Who cares what you think? So to begin, right? Yeah.

Mid-1800s. Barring my singing. Your singing made me sick. It made me physically sick. Luckily, we're not filming this one because there's a bucket next to me. It's filled. Filled with vomit because of your singing.

Mid-1800s, there's a physiologist called Klaus, like Santa Klaus. Klaus, isn't he the guy from the World Economic Forum? Is it? Yeah. I don't know. I don't watch the news or politics. Okay. That's probably a smart thing to do, really. I think so, too. Yeah. Klaus Bernard. That also makes you vomit. At the moment, it does. Klaus Bernard observed that our internal- Named after the dog? Yeah.

What dog could Klaus be? Saint. Okay, I'll stop interrupting. Go, Michael. You know what people keep saying to us is that stop interrupting, and I actually always thought it was me, but I actually think it's you that interrupts most of the time. All right, I'm going to actively... Shut your mouth? Stop that today. Okay. In 1800s, physiologist Klaus Bernard...

made an observation that the internal environment of the body remained pretty stable despite the environment around the individual changing, right? And we know all the time that the environment's trying to knock us on our ass. Heat exposure, cold exposure, heat.

So many different types of mechanical stimuli, a whole bunch of things, right? And these things can push us out of whack. We know that our body likes to exist in a happy, healthy range that we call homeostasis. Every function has a range, whether it's breathing rate, so breathing rate, heart rate, oxygen levels, blood glucose levels, blood pressure levels.

There's not a single value, it's a range. And so luckily our body has developed or evolved these mechanisms, these control systems to maintain a constant internal environment regardless of what's happening outside. That's called homeostasis. But you know what, Matt? To begin, I would love for you to give me a more specific definition of homeostasis. Well, saying half of it,

So the stasis part is standing still. Yep. Hence jewel. And the homeo, which is like homo sapien, means similar to. Well, it's not called a homeo sapien. It's a homo sapien. So it's actually very different. Homo means same. Oh, there's the same derivative. Let's say. No, no, no. Homeo means similar. Yeah. Homo means same.

Okay. So it's a similar standing. Similar standing, yeah. If it was homostasis, that's when it's one value it must maintain. That's a good point. But it's not. It's a range of values because it's a similar set. I like it. I like it. So similar to standing still. So that means it's a biological system or biological process that self-regulates to adjust the internal balance.

Generally, in response to the external. Through multiple feedback mechanisms. That's right. That's important. So there is a concept called steady state, right? In probably more so referred to in exercise physiology than other disciplines. But steady state and homeostasis have similar overlapping but pretty distinct meanings, right? So tell me...

Define steady state for me and then let's compare and contrast the difference between our body maintaining homeostasis and our body maintaining a steady state. So steady state refers to a steady unchanging level of some physiological variable. So you could say this could be blood pressure, it could be heart rate, it could be blood, just temperature, body temperature. But that is generally...

referring to like in today's series or these ongoing series is referring to exercise. So when you exercise, you're using your muscles, skeletal muscles, which then... I am at least. Questions remain... I'm using my smooth muscle. Yep. So I'm holding on to... Your bowels. Bowels. You're trying not to release your bowels when you exercise. Bowel and bladder. That's my main concern when I'm...

And everyone else is in the gym. So when you exercise, skeletal muscles generate as a byproduct of contraction, generate a lot of heat. Yeah. And as a result, your body temperature will go up. Now, that could go to the point that it exceeds homeostasis. So no longer are you in the homeostatic range of...

Body temperature. Even if your body tries to maintain it. Even though it tries to. So obviously when you're exercising, you sweat in and you generally go in red because you're vasodilating to try to dissipate the heat. You began red, but you got redder. That's right. I'm not very good at that. But the steady state is, you know, you've exercised for 30 minutes and your body temperature is now plateauing off at that point.

level of let's say 38 degrees Celsius and it will remain there as long as you kind of maintain that level of intensity. All right. So do I have it right in saying that, let's say I go outside to do some exercise. I start to move, my temperature goes up.

And homeostasis and the mechanisms of homeostasis kicks in to try and bring it back to the happy, healthy range by sweating, vasodilation, things like that. But if I keep exercising, there's no way my body can maintain my body temperature within the homeostatic range. So it keeps going up because I continue to produce heat that my body can't dissipate fast enough.

But I hit a point, the steady state point, in which the heat production is balanced by the heat dissipation and it remains at the same point of about 38 degrees. It doesn't just exponentially continue to go up to 40, 50, 60 degrees. It maintains a steady state. Correct. Okay, great. And then obviously when you start to become a trained athlete. Yes, I know you're looking at me. You will start to become more efficient at.

maintaining that steady state. So you are adapting and you may, depending on the environment that you're exercising, even...

Acclimate. Is that the right term? Yeah, acclimate. We'll talk about acclimation shortly. Let's talk about... Because then obviously as a non-athlete, your ability... That's right. Your ability to hit that steady state and maintain it for long periods of time is less. Yeah. And so instead of waiting for an athlete being able to do it for hours, like me that can do it for five minutes. If that. Yeah, I've seen you do burpees. And then you overheat. Burpee. And then you overheat and...

end up in hospital with heat stroke. Exactly. Now, homeostasis, the, you know, these control systems of the body, right? Uh,

Let's give ourselves an example. So you spoke about heat, right? And we very briefly touched upon it, but let's talk about, let's go through it stepwise, right? Let's give me an example of how heat can be maintained with a thermostat, like in a house mechanically, and then let's relate it to the body. And then let's talk about the various components of homeostasis. So let's talk at the house. You've got air conditioning unit,

What happens? Okay. All right. So let's go to the Todorovic household. Right. We're in the middle of summer here in Australia. Yep. And 40 degree days, quite a lot of humidity. What do you set your house to? Don't. Shut the doors, shut the windows and...

Make everyone do burpees all day. Open the fridge. Exactly right. No, no. I make my family suffer during the heat wave. No. I have the air conditioning probably set to 22 degrees Celsius. Okay. Not Fahrenheit. It's too cold. That would be very cold. I don't even know what that would be because just like the rest of the world, we use metric. Sub-zero.

Sub-Zero. Celsius. My favourite Mortal Kombat character. Was that Mortal Kombat? Mine was Raiden. Of course it was. What did Raiden say? Did you see the meme of Raiden for Melania Trump? With the hat? Finish him.

So, okay, thermostat, my house, 22 degrees. That's where it's set, right? But let's just say that the temperature in my house is going up. What happens? Okay, so somewhere in your house, I don't know where it is, there is a sensor that picks up the ambient temperature of the room. Yeah. And you've set that at 22, okay? Yeah. So there's a thermometer, a digital thermometer in the room that picks up the temperature. Okay.

And somewhere further in the house is a control center, which is the computer for the whole system. Now that you set it at 22 degrees. So it's locked in its system to go any fluctuations outside 22 degrees. I will perform an action. Okay. And so the temperature rises in the house because it's hot outside. So let's say it goes up to 24 degrees.

That sensor, that's the one that picks up and says, hey, we're above what we should be. I'm going to send a electrical signal to the control center, which is probably a chipboard or something. Yeah, because that makes sense, chipboard. That's what they call it. What do they call it? Like a micro...

Yeah. Anyway, the control... You obviously don't know what you're talking about. The control centre then says, this is outside the range, I need to generate an effect. So it will then activate an effector. The effector in the air conditioner, I think, is a compressor and that changes the way that the...

The fluid in the... Oh, here we go. ...moves around and causes... Is it exothermic reaction? I don't know. No, exothermic releases heat. Heat. Or opposite then. And then that cools the air flowing through it into the room, cools down the room. Okay. Sounds more complex to the... That's a combination of how an air conditioner works from an engineering standpoint. From a fridgie. All right. Human body. Okay.

Each textbook's different, right? Some textbooks say there's three components. Some say there's five. Some say there's six. Some say there's seven. Some say there's 21. I don't know. I'm making this up. But the point I'm making is that the components of homeostasis are the same. It just depends on how many you want to name. Yeah. So let's just go through the components of homeostasis.

that need to be activated and work efficiently for us to maintain the happy, healthy range of, again, let's say temperature. So my body- And so the temperature is- My body temperature is going up, right? So you start. It's also important to state homeostasis.

Yeah, you said it as a range. So it's not always just a particular value. I've definitely said that multiple times. So temperature isn't just 37 degrees flat, which is I think 98.6 Fahrenheit. Oh, very good. Thank you. So it's just not that and that's it. It's a range of 36.1 to 37.2. As long as it sits in that range, it's happy. Okay. Okay. So when we look at the homeostatic process or biological system,

We have the stimulus. Are we going hot here? Hot. Okay, hot. Hot, baby. So the stimulus is hot. Yeah. The temperature's hot outside. It's getting hot in here, says Nellie. So then... You take off all your clothes. So then we need a sensor that picks up the heat. Now, there'll probably be some on your skin, thermoreceptors. Hope so. That will pick up and go, hey, just walked outside. It's hot out here.

So that's going to cause a neurological impulse back to your brain to say outside's hot. But there's also going to be sensors, thermoreceptors in the inner part of your brain, which is going to be the hypothalamus, which is a structure what diencephalon behind your eyes. Now, if you go...

kind of deep to your eyes. Would you say that? How would you locate the hypothalamus? Yeah, that makes sense. Ballpark? It's at the bottom of the brain, deep to the eyes. Yeah. So here in the hypothalamus, you'll also have femoral receptors that pick up basically the temperature of blood.

Now, this is where it's a little bit confusing because the control center is in the same location. So the hypothalamus is also the control center. So there's going to be probably a paracrine or some juxtacrine or maybe even a- Don't need to get too complex. Just talk about- Within the same. So the signal is just within itself that then says to the control center, hey, we should be set at 37 or 36.1 to 37.2. We're now getting hot signal.

We need to respond to this. So we need to then send a efferent response. So efferent's away from the control center. Would you define it as that? Yep. Yep. So that would be a neurological response, a nerve signal, which then goes to the effectors. The effectors are going to be both, mostly at the surface of your body. So...

Sweat glands and blood vessels in your skin. And they are going to release sweat onto your skin and also dilate blood vessels just under the skin. Okay. So to take that 20-minute explanation and make it 10 seconds.

You've got a stimulus, which is the change in the environment, picked up by a receptor. The receptor transduces the signal and sends it to the control center through what's called an afferent signal. The control center makes a decision as to what it wants to do and sends an efferent signal out to the effector, which elicits the change. In this case, the signal...

stimulus was an increase in temperature. We want to obviously negate that and drop the temperature down. So the effect is going to be sweating or vasodilation. That's right. Okay. So I made that simple. So that is where the stimulus is negated.

Through the effector. That's called... It's the opposite direction, right? Negative feedback. Negative feedback. And there's a lot... Most of the homeostasis that you do in the body is through this mechanism. Some common examples with temperature, sugar, blood sugar does the same, blood pressure does the same, oxygen, CO2, a lot of hormones, they all work through negative pressure feedback. And can I... Negative pressure feedback? Negative feedback. Negative feedback, okay. Okay.

But can I also highlight that even if the stimulus was a drop in temperature. So cold temperature. Cold in temperature. And obviously the outcome is to warm you back up, to bring you back to homeostasis. Even though that's increasing, that's still negative feedback. So remember that negative feedback is negating the stimulus, doing the opposite of the stimulus. Stimulus is to make it go up. You want to bring it down. Stimulus is to go down. You want to bring it up. But we know that there's a term called positive feedback. And.

And positive feedback is when the stimulus is not negated but exacerbated, amplified until the stimulus disappears, which to me sounds weird. Counterproductive. Yeah. Why would you amplify the stimulus to get rid of it? Can you think of any examples in which this is the case? Yeah, blood clotting. Right. So you've got a leaky blood vessel. Do I? You want to generate a clot to the point that's not leaky anymore. Yeah.

And then it turns off. You don't want to keep clotting because then you're going to block the whole body out. But doesn't positive feedback tell you to keep clotting? Isn't that the stimulus is to clot? And then that tells you to keep clotting? Yeah, keep clotting, keep clotting, keep clotting until the initial. I want to say keep clotting five times fast. Keep clotting. Keep clotting. It's turning into clotting. Clotting, clotting, clotting, clotting, clotting. No, keep clotting. Keep clotting, keep clotting, keep clotting, keep clotting. You sound like a horsey. A horsey?

Clip cloppy, clip cloppy, clip clop. Go on. Yeah. So the stimulus probably correct me if I'm wrong here, cause I'm, I'm sure you've lectured this recently, but the stimulus that leads to the clotting to begin with is injury to a blood vessel, like exposure of collagen or something. Right. And so as soon as you cover that up and it turns off essentially. Yeah. Um,

is one. Yep. And then childbirth. So childbirth is the best example I can give close to firsthand. Does it count firsthand if I was holding my wife's hand at the time? No. Uh, that, was it a left or right hand? Uh,

Can't remember. Left side of her? I wouldn't call it first hand. I'd call it left hand. Yeah, left hand. Yeah. Left hand experience. Definitely not first hand experience. That would probably be quite dismissive and insulting to mothers who actually have to go through the birthing process. But let's go through it. Because you didn't have to go through that process. You just stood there and held your wife's hand. Correct. Right.

I was a great support though. I was a great support. She said I was great support. Didn't the midwife kick you out? No. Didn't the midwife want to kick you out? Actually, the second midwife was an ex-student of mine. Really? Yeah. So she wanted to kick you out. You know, she was very professional in the sense that she didn't acknowledge that until her shift was over. Oh, wow. Yeah. That you were the worst lecturer she's ever had. Yeah, yeah, that's right. Just wanted to say, your wife's leaving. I'm going home for the night. Okay.

Just letting you know, I was a student. You were horrible. You were the worst lecturer I've ever had. That's right. You taught me nothing, thankfully. All right. What were we talking about? Oh, positive feedback. So talk about the birthing process secondhand. Right. So for our second daughter, Halima, Zabin, my wife, woke up somewhere in the region of midnight with pains.

Contraction pains. We're starting early, aren't we? Yeah. But mind you, she did deliver fast. So anyway, she woke me up. I was like, oh, take it easy for a bit. Anyway. I'm going to bed. I'm tired. So the initiation of the birthing process had begun and the head of Halima was pushing against Zabin's cervix. Okay. Okay. So that stretch, so that's the stimulus stretching and it would be a neurological signal. Okay.

So the mechanical force of the stretching of the lower part of the uterus is then picked up, as you said, transduced into an electrical signal sent up to Zabin's brain, which then activates again the hypothalamus, which then goes down to the pituitary gland to release oxytocin.

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Trade in your old phone for a brand new iPhone 16 Pro, iPad, and Apple Watch. Visit Verizon.com today. Additional terms apply. Service plan required for Apple Watch and iPad. Does it ever feel like you're a marketing professional just speaking into the void? Well, with LinkedIn ads, you can know you're reaching the right decision makers. You can even target buyers by job title, industry, company, seniority, skills, etc.

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Which you nearly were. So oxytocin is now in the blood. Yeah. Okay. And then acts on smooth muscle throughout the body. But in this case, it goes to the uterus to tell the uterus to contract. Now, contracting the uterus is going to push the baby harder against the cervix. Ah, so there's more stretch. More stretch. Right. More activation of hypothalamus, more oxytocin. So see how it's amplifying it? Yeah, yeah, yeah. So then...

It's about 12.30 and we're now in the car. Yeah. And I've noticed that the contractions have become more significant and closer together. Oh, okay. The oxytocin is bumping up. And so by the time we get to the hospital, you know, quarter to one, the midwife has a look at the dilation. So you went and grabbed a coffee and a banana bread and then checked her in? Well, I didn't even – I almost had no time to park the car. Wow. So –

I think she was five centimeters and then dilated. Yeah. Not tall. And then within the space of another hour, the baby was out. Really? Yeah. It was very fast. The second one. My wife's label was 30 hours. That was the first one. The second one was cut out.

Okay, so the point we're trying to make here is that... That's positive, all in one direction. Until the baby's out. Until the head's out. There's no more stimulus. No more stimulus. I don't know how the placenta pass works because that's not presumably the same mechanism, but there's probably some degree of... That slops out afterwards. No, but what initiates the contractions of it? Probably still oxytocin. But I mean like there's no...

Stretch in the same way. It's probably just attaching and then something else is irritating it. Pulled out with it. Okay, so we've got positive feedback. All right, so we spoke about negative feedback, positive feedback. There's another term which is used with, again, very much within exercise physiology, which is… Apathetic feedback. Not apathetic feedback because that was the feedback you got from your wife after you helped her give birth, quote unquote helped her give birth. Poor thing. Matt's wife is wonderful, by the way. Zabine, I have no idea why she's with Matt.

Gain of the system. This is the term. So,

Gain of the system is the precision, the term's precision, man. It sounds like you in the stock market. The precision with which a control system maintains homeostasis, the precision, right? So it's a calculation, calculated by the correction. So let's just say you've got some degree of homeostatic change, right? Let's say temperature.

and the body needs to correct it, right? That's the homeostatic response. It's not always perfect correction. So there's a degree of error. So you take the correction and divide it by the error and the number value you get is called the gain of the system. And the higher that number, the tighter or more precise the regulation is. So let me give you the temperature example again.

My body temperature goes up by five degrees. I overheat by five degrees. My homeostasis mechanisms that you spoke about kick in and it corrects it by 4.5 degrees. So it only brings it back down 4.5 degrees. That's the correction. The error is 0.5 because that's how far off I was from being perfect. So you take the correction, which is 4.5, divided by the error, which is 0.5, and you get nine. That number is relatively high and therefore...

the gain of the system is quite precise. Okay. And you could make an argument that the more tightly controlled a homeostatic function is, so the more narrow the range for it to be happy and healthy, the greater the gain would be, right? The greater the value for the gain would be. There's going to be other values where it's like, yeah, it doesn't have to be tightly controlled. Therefore, the gain doesn't need to be as precise. And could this gain, I know it's not here in this calculation, but could it also be

over time? I don't know. To also demonstrate the speed of precision? Because I'd imagine- Maybe. With some of these mechanisms, these homeostatic mechanisms, as I've illustrated, I think, yeah, I have illustrated, there's examples where there's neurological signaling and there's hormonal. Yeah. Now, my guess would be hormone-

Both are communication methods in the body, right? Yeah. But one's super quick...

and super localized, whereas hormonal is slower, longer lasting, but more widespread. Yeah. So could you assume that, say, a hormonal response or a homeostatic response that requires hormones might be slower and less precise in its gain than neurological? Maybe. So like blood pressure...

Which is, you would say is mostly, I know it's not perfectly, but mostly is neurological, right? Yeah, yeah. Because of the change in diameter of the vessel. It's really, its gain is very precise. Yeah. And it's, therefore you have to really maintain that range very well. Yeah. And if you don't, bad things happen. So for me, as you mentioned almost in every podcast, I pass that when I vomit. Yes, very funny. So the...

The gain normally in blood pressure in my body is fine. So I'm not passing out every minute of the day. But for whatever reason in –

the process of vomiting, that gain is a little, or the error is a little bit out of whack and I'm passing out as a result because it hasn't corrected it well enough. Yeah. Well, that brings us to the fact that when it comes to homeostasis and all those control mechanisms you spoke about, right, the receptor, the control center, and the effector, the three main components, dysfunction in any of those three is

will result in disease. So all disease is is when homeostasis doesn't work, right? That's it. That's why it's such an important concept in medicine but also in health and fitness because your body's also trying to maintain homeostasis. We're going to talk about adaptation and things shortly. But can you just briefly talk to us about when some of these mechanisms –

sorry, diabetes is a great example for you to use where you can actually focus on where each of these components are dysfunctional and how it results in the disease. Yeah, so diabetes is a breakdown of a negative feedback mechanism being blood sugar levels and the

I mean, it's too broad. I know there's many more now, but generally there's two broad categories of diabetes, type 1 and type 2. With type 1, what's happened is your immune system has essentially killed off the beta cells in your pancreas. Now, the beta cells play a

a dual role. They play the role of a dual, again, dual, uh, they play the role of a sensor sensing them. So they're kind of putting their little tongues out into the blood and tasting the sugar. Funny you say that. Cause that's how we first used to diagnose it back in the 1800s. That's urine though. I'm sorry. Um, so they're tasting the blood for sugar, but then they're also making sense of it and responding with insulin. Um,

Type 1 diabetes, you've killed off the beta cells. So no longer do you have anything to sense blood sugar, but also you don't have any control center to release the effector. So the receptors and the control center are dysfunctional in type 1 diabetes, resulting in the disease of type 1 diabetes. Right, which is generally high blood sugar, but other poor regulation of metabolic processes.

Products, right? Like fats and proteins. Okay, top two. Top two is your sense is okay, your control center is generally okay, you release insulin, you don't respond well to it anymore. Yeah. That are kind of in the effectors. Yeah, that makes sense. Yeah. Which is, yeah, and you can pick any disease and you'll see at what point in the homeostatic mechanism or control mechanisms do these things not work. And then you can take a look at...

From there. So what I want to talk about now is that exercise is a test to homeostatic control, right? I do it every day. Uh, sorry. I do it every day. I test the precision of my homeostatic mechanism through exercise. Really? Yeah. Walking, walking to my office from the car. I was just going to say getting out of bed and walk into the bathroom. Sure. Um,

So the test is the fact that it disrupts like so many homeostatic variables, right? So contraction of muscle leads to increased heat, increased demand for oxygen, increased demand for ATP, so energy, increased production of metabolic products. These things are knocking our body out of whack. Okay, I've got one for you. Okay. Question. Yeah. Does that count as an interruption?

Look, go for it because I haven't finished my point, but you keep going. All right. So at rest right now, which you're currently at. Well, that's arguable. The amount of, what's the volume of blood in your body, do you reckon? Six litres. Six litres, all right. So from the six litres that's pumping around your body right now, what percentage would go to your kidneys?

20%? Yeah. 15, 20%? I'd be the same, yeah. What about your brain? Yeah, 15, 20%. Okay. Now, what about your skeletal muscles? Yeah, probably 15, 20%. Yeah. Okay. Is that right? That's about right. This is at rest? At rest. Okay. Right now. So of the amount of blood that gets pumped out of my heart every minute, the cardiac output? It's about... What's that, five litres? Yeah.

Well, you said six litres. Well, that's the total volume of my blood, but you asked what my total volume of blood is. You didn't ask what my cardiac output was. Okay. So cardiac output, five litres. So my heart pumps out five litres a minute. So you're saying that every minute, 15 to 20% of the blood. A litre of blood goes to your muscles, right? At rest. At rest. Okay. Okay. That makes sense. What point are you making here? Okay. Now, if you were to do the most intense...

you can think of. What would that be? Something that you couldn't even imagine doing. What workout have you done that you're like, that's the craziest I've ever done? Sled runs. No, no. There's a workout in CrossFit called Fran.

Have you heard of that? No. Okay. Is that an acronym? No, no. It's what they call a girl benchmark WOD, but it's not for girls. It's just the earlier CrossFit workouts had girls' names and guys' names. Okay. Right? And Fran was one of the girls' names. So have you heard of a movement called a thruster? Yeah.

But like what the rugby league players do with like, Oh no, I don't want to talk. No, no, no. They get arrested for that. Like to improve tackle. Oh, uh, are you talking about like a hip thrust? Yeah. No, no, no. So no, like they kind of grab something, twist and then throw it. Uh, no, it's not that. And don't break the microphones. So a thruster is a strain, uh, football sport, by the way. Very good.

You take a barbell, right, with weights on the side. So let's say 45 kilos, which isn't overly heavy, but it's 42 and a half kilos if you want to be specific because it's 95 pounds, right? Yeah. You take that barbell and you do a clean. So basically you bring it from the ground to your chest and then you go into a full squat and then you stand up

and press it overhead. Okay. And so from that overhead position, you go, you bring it back down to your shoulders and back down to a squat. Yeah. And then you stand up and push it above your head again, right? Wow. So that's a thruster. You needed to know that. The next movement, so there's only two movements in this workout, thruster and a pull-up.

Right? And with the pull-up, your chin has to go above the bar. Okay. The workout is as fast as possible. You do 21 reps of each of those. So you do 21 thrusters, then 21 pull-ups. Then you do 15 thrusters and 15 pull-ups. Then you do nine thrusters and nine pull-ups. That's it. It takes... Until you finish. Yeah, it takes like five minutes. Right? The workout's like...

I mean, the fastest time I think is like three minutes or something. I can't remember. Have you finished it? Yeah. I've vomited every single time I've done it and I never vomit in workouts. Okay. It's the most sickening combination of movements. Okay. Hold the vomit part for a second. Okay. Well, not right now. Like in the bucket that I vomited from your singing? That's right. Let's go now to that movement. So for how long did it take you to finish?

I think it was under five minutes, four minutes. Okay. So let's say at the four minute mark. I think, look, people are probably going to email and go, no, the world record is like six minutes. I can't remember. This was years ago, but I haven't done it since because I'm scared. Okay. So let's just say it takes five minutes in the four minute mark where you're at your heightened level of intensity. Yeah. Now what's the blood flow to your muscles, clear the muscles?

As a percentage? Yeah. Of that five litres? I don't know. What is it? 90%. Oh, so it's gone from being one litre to closer to like 4.8 litres. Yes. Right. And can I also add...

Not only does the percentage of the cardiac output go up, but the absolute value of your cardiac output goes up. So your cardiac output, so the amount of blood your heart's pumping out every minute, is no longer five litres. Oh, yes. It's now like 20 litres. Your heart's now, because it's pumping so hard and so fast, 20 litres of blood. So you're getting...

So of the 20 litres that are pumping out, 90% every minute is going to the muscles. So you're getting effectively like 18 litres of blood every minute just going to your skeletal muscles from doing thrusters and pull-ups. That's right. And that would all be based on homeostasis trying to regulate sugars, electrolytes, energy, oxygen, removing carbon dioxide.

And because you're producing so much ATP, you wouldn't be efficiently delivering oxygen aerobically. So you're now probably going anaerobic as well, producing the lactate, going...

And that's probably why you're vomiting, right? Yes, exactly. And so... And again, that would be a homeostatic mechanism to the stressor. Yes, and this is a great... This leads in to the point I was going to finish. That was actually a very good interruption and I appreciate it and feel free to do that as many times as you like, Matt. Do appropriate interruptions.

Because this is important, that exercise rarely results in you being able to maintain homeostasis during that activity. So when I'm doing Fran, that workout... Didn't work out well that one. When I'm doing that workout, I can't maintain homeostasis. I can't bring all those things back to their normal values, their normal resting state values.

And also we spoke about steady state, right? That, okay, well then I'm probably maintaining a steady state. You can rarely during intense and prolonged exercise, can you even maintain a steady state? Well, how would you be able to do that when 90% of your blood is going to your muscles? Exactly. And I've got so many muscles, right? That's the point you were making. We've got so many muscles and there's 650 of them all been activated at the same time. Well, I hope not. I'll pop. But, um,

So what happens is you can't even maintain homeostasis, can't even maintain a steady state, right? Because the production and the output are not equivalent. You're producing more than you can output. So you can't even maintain a steady state of any of those things. So you eventually reach fatigue and that results in the cessation of the exercise. You stop and then your body can be brought back. And vomit. Yes. Now, um,

Importantly, when the body's placed under stress, it can adapt. And the aim of this adaptation is to cause a better maintenance of homeostasis next time that person is exposed to the stressor, right? Or the stressor is exercise. So it's important to say that exercise is good for us, but it's because it's a stressor

And our body adapts to it so that we get bigger, fitter, stronger, healthier, so that next time we're exposed, it's not as potentially harmful for us, right? So let's talk about adaptation. Can you define it? No, I'll define adaptation. No, you basically did it. Structurally and functionally responding to the stressor so you're more efficient for next time.

Yeah, that's pretty much it. Cellular and tissue-wide. Yeah, it's a structural change. It's a functional change of either a cell or an organ system that results in an improved ability to maintain homeostasis during stressful conditions. So that's adaptation. But not all adaptation is beneficial. No. You can have adaptation that is helpful and adaptation that is probably trying to be helpful. The purpose of the adaptation isn't to harm you. It's to try and maintain homeostasis.

but ultimately fails. Can you give us an example of each? So a useful one? A useful one and then a dodgy one. Staying in the gym, a useful one would be resistance training. Come on off the top of your head. Which gym? It's called Matt's Shed. Oh, here we go. Is that where you like clean your goats? I got no goats left or chickens. All my chickens got eaten by foxes. Really? Yeah. Fox, fox. How do you know it's one fox? I don't know actually.

You know, so it happened in two situations. First time the fox ate five, just basically killed them and bit their heads off. But didn't bother cooking them. No, didn't cook them, didn't pluck out the feathers that just left the carcasses strewn all over the yard. Disgusting. And then I took Zerena down, my three-year-old, and we buried them. It got her. We buried them. And she wanted to know why they...

Had no heads. Oh, yeah. And what did you say? I told her. And then she'd always ask questions about foxes. Oh, you didn't make it a life lesson and go, this is what happens when you don't clean your room? Yeah, when you don't leave a note. You always leave a note. But one chicken survived. To tell the story the fox said, I'm letting you survive to tell the others. Right? Like in every bad guy movie, this is so that you can tell the others who I am and what I do.

I like that. Johnny Fox. Johnny Fox, Foxville. Nice. Anyway, it survived, but it was because it was on the nest. It was broody. So it must have just escaped the detection of the fox. So all the rest were like, yeah, all the rest were on the perch. It was in the nesting box. Even the rooster got done in? Oh, the rest was long gone.

Anyway. What do you mean? Had died a year ago. From what? Old age. Oh. Poor homeostasis. Yeah, well, that happens with age. As you get older, your buffering capacity. Your reserve, yeah. Physiological reserve diminishes. I'm not sure the audience will be enjoying this. But anyway, the take-home point is one survived. That's not the take-home point. No one cares about this. One survived and survived for some time. Now, Zarina got...

accustomed to feeding this one chicken. She was like, oh, she felt sorry for her. Anyway, the other day it was also killed by the fox. Oh, no. And I'll say to Zerbine, how are we going to talk to Zerina because she's potentially attached to the one chicken. Yeah. I'll just tell her. So Zerina got up and went like, oh, I guess bad news, bad news. Like what?

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Wait, did I say job title yet? Get started today and see how you can avoid the void and reach the right buyers with LinkedIn ads. We'll even give you a $100 credit on your next campaign. Get started at linkedin.com slash results. Terms and conditions apply. Fox was back. This is her response. Was it the same Fox? Oh, nice. Not sure. Didn't interview them. Okay.

Is it missing a head? Oh, wow. Okay. She's putting it all together. So she wasn't too upset? No. No. But she was very literalistic. Yeah, very much so. Just like you. Yeah. Yeah, very much. So no emotion. That's true. Just like you, just matter of fact. Very scientific. Very scientific. Yeah. Okay. If it was me, I would be distraught. Tears.

Because I love my chickens, which I don't have. So actually, I stole yours. How did we get on that topic? Who knows? Now, we're talking about adaptation and we spoke about it's the body's ability to change structure and function to result in an improved ability to maintain homeostasis during stressful conditions.

I wanted you to provide a positive example and I said do you go to the gym? I think that was your interruption this time. Okay, so keep going. Positive. Yeah, so positive would be in resistance training in the gym because you are being physically slash mechanically stressed by the lifting of the weight your muscle becomes

maybe injured to some degree. Maybe. Not always has to be. And this leads to an adaptation where the cell, muscle cell, grows in size. So it lays down more muscle.

which are protein-like, and that causes the actual size of the cells to increase in size, which is called hypertrophy. Don't have to say it like that. Hyper means increase, trophy, growth. Why is this beneficial?

Well, it then overcomes that stress or better responds to that stress next time. Okay. Makes sense. People go to the gym because they want hypertrophy, right? All right. So that's a positive adaptation to a stressful event to maintain homeostasis. What's a negative adaptation or a potentially detrimental one? Okay. There's four...

Four main categories of adaptation. There's hyperplasia, hypertrophy, atrophy, and then there's metaplasia. This is the example I'm going to give you. Meta, what's meta mean? Meta means change, doesn't it? Yeah, maybe. So this is metaplasia. So this is change your growth. I can see atrophies happen to you. Okay.

So I'm just going to let that go through because that's an interruption. Now, metaplasia is a change in cell type. Okay. Okay. So an example here would be in the esophagus. The esophagus normally is just a pipe that...

food from the mouth to the stomach. I bet you if it heard you say that, it wouldn't be too impressed. Be insulted. Yeah. So it just has the lining, the cell lining of that pipe is a bit similar to your skin, right? It's got stratified squamous cell that...

because there's a lot of abrasion as you swallow, it can repair itself that way. Especially for you, you don't chew. So you swallow things whole. But when you go into the stomach, the line in the stomach is a bit different because it's very acidic. So it's the environment in the stomach, very acidic, very potentially damaging. So the line in the stomach is more columnar.

Column shape. And so when the esophagus is getting maybe leakage from the stomach, which is called reflux, so acid's going back up into the esophagus. Some people have this as a condition, and that is causing irritation to the esophagus. The esophagus goes through metaplasia where it changes its cell structure type into a more columnar type of cell. Is that because it's thinking, hey, I...

Don't get exposed to acid. I can't handle the acid. I know the stomach can. And the cell shape that it has is columnar because it produces mucus to protect itself. I'm going to change my shape to columnar in the hope that I'm protected as well. But the cell shape change that it induces, which is its adaptation, doesn't help it.

It'd probably help in the short term. Yeah. And so if that was reversed, it probably would have been quite beneficial for it. So what's the problem? But the problem is because you're changing the activity of the cell and what the cell is actually doing from a, what do you call it, mitotic. So it's a cell cycle kind of nature. It pushes it into a potential or a risk that it can actually become...

Ah, yes. ...and become dysplasic, which is disordered, and then it might cause a more cancerous-like growth. Gotcha. So the adaptation being the metaplasia is an attempt to maintain homeostasis in response to the stress, which is the acid, but...

It's probably successful in the short term, but long term it can be damaging because it can lead to potentially cancer. Okay, great. Now there's another term, Matt, which is similar to adaptation, bit of overlap, but it's quite distinct. That's called hormesis. So anyone with exercise physiology has heard the term hormesis before. Now this is a dose-dependent hormone.

beneficial response to mild stress where too much stress is harmful, right? So one, it's dose dependent, meaning that you need to expose the organ system or structure to that stressor in a low to mild or- Goldilocks zone. That's right. And that's enough to lead to an adaptation that's beneficial, right? But too much, harmful. Does that make sense? All right. And generally speaking, it's

Short-term and more biochemical, right? So not gross. The gross physiological changes that occur are the adaptations. But hormesis tends to be a short-term, biochemical, dose-dependent, beneficial response to a mild stress. Okay. Right? Now, so we've got adaptation. We've got hormesis. There's another term, and this is called acclimation.

Now, acclimation is, again, very similar to those two. Bit of overlap, but distinct. It's short-term, so that's similar to hormesis. Key difference here, it's definitively reversible, right? It's reversible. It's a reversible adaptation. Well, the adaptation may not be reversible. Exactly. Exactly.

And it's the physiological adjustment to an environmental change. So that might be you're exposed to a really hot environment or a really cold environment, for example. So acclimation is your body getting used to that environment by eliciting a number of changes. So can I give an example? Can I give two examples? Please do. All right. First is high altitude exposure. What's the highest altitude you've been? When I climbed...

The Inca Trail in Peru. Machu Picchu. Yeah. How high is that? Do you know off the top of your head? It's above 4,000 metres. Is there anything in Australia like that? Do Australian planes probably fly at 4,000 metres? Yeah, yeah. 30,000 feet, which is Everest. Okay. 8,000, I think, right? 8,000 metres? 8 metres. So you climbed half of Everest? Yep. Okay. That's a nice way of putting it. All right, so...

Up there, let's talk about adaptation, hormesis and acclimation, right? So the adaptation could be that remaining at high altitudes, you potentially over time could develop larger lung capacity and a higher hemoglobin level.

Yep. Right? But that would be some degree of reversibility in the hemoglobin at least, right? That's fine. That's fine. I'm just talking about the way your body is. Remember, all adaptation is is a structural or functional change that's occurring to try and maintain homeostasis in response to a stress. And there probably would be also... A low oxygen environment. Probably also be epigenetic changes, right? Yeah. That would be...

Maybe lifelong lasting, right? Yeah, yeah. Hormesis, what hormetic changes are occurring. So again, short-term exposure to this hypoxia, this could enhance your erythropoietin levels, EPO. So this is transcription turning on a gene that enhances the amount of red blood cells you produce, right? So that can be a hormetic change. One, it's beneficial, it's short-term, and it's biochemical, right?

Acclimation. Acclimation is a person spending, let's say you spend a few weeks at that high altitude. This is going to increase those red blood cells, but

It's reversible when you go back home, right? So the acclimation is I'm getting used to this environment physiologically by increasing my red blood cells. You could say, well, that's adaptation or that's hormesis. Yeah, it is, but your body getting used to that environment is the acclimation. And then when you go back, it's reversed. You just go back to normal, right? So that's why it's so much overlap. And so let's use another example for exercise, right? This is more specific to the audience that wants to hear about exercise.

The adaptation to exercise. So let's say long-term endurance training, that's going to increase your cardiovascular efficiency because your heart gets better, you increase your blood volume, the way your muscles contract becomes more efficient, the way oxygen gets exchanged, all those types of things, right? So these are the long-term adaptations to endurance training. Hormesis, you'd say that a single intense workout might trigger mild oxidative stress or

which activates protective pathways like the activation of heat shock proteins. So that's the hormetic change. It's beneficial. Acclimation. After a few days of training in a hot condition, your body might improve its sweating efficiency and its ability to thermoregulate. So if you were to continue to do your endurance training, you went to a hot, humid location, the adaptation or the acclimation to that new environment would

would be the distinction. So you're just becoming more efficient at thermoregulation at a hot, humid environment. Yeah, that's your acclimation. Because again, acclimation, all it is, is about the physiological change that occurs in response to the external environment. That can be an adaptation. In the short term, that can be hormesis. So there's overlap. So as an example, if you were an Ironman athlete,

Triathlete. Yeah. Triathlete. Call me Tony Stark. And so if you were competing, let's say at...

Let's say Hawaii. No, Hawaii is going to be my example. But let's just say Victoria, Australia, which is temperate, right? And you would adapt to that type of activity over long periods of time. So you'll now become more efficient to perform those three legs of exercise. Okay. Well, swimming, cycling, running, right? Yeah. If I had three legs, I would do way better at it. Okay.

Now you might perform fine for that particular location, but if you then went and competed, like you said, in Hawaii where the environment's totally different, you may not get through the Ironman because heat stroke. And then that's potentially life-threatening. So what you may have to do to acclimate for the event is to go to Hawaii and

a couple of months beforehand. Sounds good. So you then are... I'd love to. Yeah. You are now baseline into that environment, so then you can perform as you would have done in Victoria. Yeah. Yeah, that's exactly right. So that's the acclimation. Look, Matt, I think we've gone through a lot of key terms associated with homeostasis. We've defined it. We've spoken about adaptation, hormesis, acclimation, all the various components of the homeostatic control mechanisms.

We're setting ourself up well for the rest of this series where we're going to talk about things like bioenergetics. We're going to talk about fuel sources. We're going to talk about muscle contraction. We're going to talk, oh my God, there's so many things we're going to talk about. It's going to be great. All about exercise physiology. Are you keen?

Well, I'm still here. Okay. Not the answer I wanted, but the answer everyone got. If you want to contact us, you can. Admin at drmattdrmike.com.au. You can contact us on social media. It's just me, at drmikedorovic, at D-R-M-I-K-E-T-O-D-O-R-O-V-I-C. You can please subscribe, follow us on YouTube.

and subscribe to us and follow us on the podcast. Leave a five-star review. And also prepare for an upcoming book release. Matt and I are writing a book, ladies and gentlemen and friends and foe. We're writing a book, whether you like it or not, called Dr. Matt and Dr. Mike's A to Z of the Human Body. Put some pennies away. Yeah. I don't know how many yet. That will hopefully be released soon.

Before Christmas this year. Yeah. 2025. That's right. So get ready. Get ready. This isn't a textbook. This isn't a textbook for students to study. It is, what we've done is we've taken the alphabet, which everybody should be aware of, A to Z, and we've chosen one body part structural function,

Or a couple for each of those letters. Two to three. And they're not really the ones you may have necessarily heard of. They're a bit obscure. Some are obscure, right?

like I think one is gluconeogenesis, right? And we've written a chapter on gluconeogenesis. There's a couple of other really interesting ones, I think, and quite fun. So we try to be fun with it. At least I do. Uh, and if you would like to purchase that, please just keep listening. Cause once we start getting more information about what's happening, we will let you know. And we might be able to get from a publisher. We might be able to get early release kind of, what do they call them? Um,

Promo. Promo. Pre-sale. Pre-sales. Yeah. Yeah. But maybe we can't. So maybe Mike should shut his mouth. So let's just see what happens. If you could see Mike when I said that. I was just like, shut your mouth. We don't know any of this. I don't know how I could have adapted to that stare. No, it definitely wasn't hormesis. Thanks, Matty.

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