Welcome to the Empirical Cycling Podcast. I'm your host, Kolie Moore. Joined as always by my co-host, Kyle Helson. And I want to thank everybody for listening and remind you to subscribe to the podcast. If you have not yet already, give us an iTunes rating. Five stars, never goes amiss. Share the podcast. That's really a great thing you can do if you like what you're hearing. And we've also got no ads in the podcast. And so if you'd like to donate to support the show, you can do so at empiricalcycling.com slash donate. We have show notes up on the website and we definitely... We have some show notes for this one. We've got a couple graphics that you may or may not want to follow along with. We also have some merch up at empiricalcyclingpodcast.threadless.com. And if you have any coaching and consultation inquiries, questions, and comments, you can email empiricalcycling at gmail.com and also up on Instagram at empiricalcyclingweekend AMAs and the stories. So give me a follow there if you want to participate in that. Or you want to follow one of Kyle's cats, you can follow Millie. M-I-L-L-I-E, Kelvin on Instagram. Really good follow there. So let's get some thoughts on, because we've been kind of heading towards this. We talked about the process of breaking down fats, and from fats we get acetyl-CoA and we get NADH and FADH2, so reducing equivalence. Don't worry, we'll... discuss that again more. We'll review that. And also the breakdown of carbohydrates and getting NADH and also acetyl-CoA and lactate and yada, yada, yada. So those were the last couple of Wastock episodes. So today we're leading towards talking about what is aerobic. And I think we've kind of prefaced episodes like this before, but what other thoughts do we have on aerobic to start us off? Well, I think if you're of a certain age, the word aerobic may be ruined by like aerobics videos or like plastic steps or Jane Fonda or something like that or it's ruined by something some chart in your like globo gym that tells you you have to stay in some heart rate to be aerobic but probably for people who are Recreational or Competitive Cyclist. You think of aerobic and you think of longer rides, maybe with your friends, but generally longer rides spanning an hour, two, three, four, five, six, seven hours, and you think endurance or you think big zone two or base. Maybe people are thinking aerobic must mean base. And then maybe you also maybe think about aerobic and you think about... The actual scientific origin of the word and can think about breathing and respiration and heart rate and things like that. And actually get into what does it actually mean to use oxygen, even though when you go out and ride your bike, you're maybe not thinking like, how is my body processing all of this oxygen? But if you speak to a scientist or a physiologist, they're probably going to think, oh, aerobic means you require oxygen. Yeah, and you breathe in oxygen, and you breathe out CO2, and you make water. So, like, where do all the carbons, the C's, come from for CO2 if we're just breathing in O2? Well, we eat it. And where do all the H's come from for H2O? Well, we also eat it. So, really, this is, you know, kind of the conclusion. Well, some of the conclusion. We have a couple more episodes to go yet. where we may or may not get ourselves in trouble. talking about probably keto. We're definitely going to touch on VLA Max and all that kind of stuff. So look forward to that. Oh, yeah. So this is kind of like our, you know, goalpost on the way of kind of a wrap-up episode of Last Couple for metabolism. And, you know, this is kind of the groundwork that we're laying for other stuff, kind of like we did in the VO2 Max series. So hopefully, you know, this will all make sense about how we breathe in O2 and eat food and then... Breathe Out CO2 and water. So let's get started with a short formula. C6H12O6 plus 6O2 yields 6CO2 plus H2O. So that's the chemical formula for the breakdown, the combustion, the aerobic combustion of carbohydrates. So that's what we're doing here partly. We could do a fast formula too, but... You know, et cetera, et cetera. It should sound familiar. I'm sure everybody learned it in high school. So let's review quickly what we've been over so far with fat and carbohydrate oxidation. So fat gets transported from fat tissue through the bloodstream across several cell membranes, including two mitochondrial membranes and into the mitochondria and it's broken down into acetyl-CoA and no oxygen gets used. Carbohydrates Come from food, muscle glycogen, gluconeogenesis, you know, making new glucose in the liver and yada yada. And broken down in the cytosol, which is the main cellular compartment. So that would be your main compartment of the muscles of what we're concerned about here. And as pyruvate and lactate get shuttled into the mitochondria and broken down also into acetyl-CoA. So both of these generate not only acetyl-CoA, but also reducing equivalents, which are NADH and FADH2. So we're going to get to more details on that in a little bit. And I was thinking about, you know, better ways to call them than reducing equivalents. Like electron carriers might be a better way to talk about it, because I think we did this in the last episode where we were talking about why we generate NADH, and maybe in the FATS episode too. Because, you know, we couldn't, like, get every, like, intermediate step from breaking down carbohydrates and fats into the mitochondria, into the respiratory chain, and then back out to get broken down. That would take forever. So it's better to compartmentalize things and just have little messengers. It's like money. So reducing equivalents, electron carriers, et cetera, et cetera. For now, we're going to start with following... Acetyl-CoA, and this is regardless of where it came from. So this means that we have to talk about the Krebs cycle, which is also called the tricarbacillic acid cycle, or the citric acid cycle. It's all the same thing. And also, we're not going to go into as much detail as we did in the previous episodes, because it's going to take us as long as an actual biochem lecture, and we don't want to do that, and I'd love to do 20 hours of podcast. Actually, I'd love to do like 50 hours of podcasts on how cool all this stuff is in gritty detail. And seven people would listen to them all. Yeah, three downloads per episode by the end of it. Like, are they ever going to mention FTP again? Sorry, we're not. I'm just kidding. We are going to get to FTP in this episode, actually. And so when we're done with the Krebs cycle, we're going to have more, and you'll see why. But at the end of these things, even if... you're don't have like if you're in the car or you're on your bike hopefully you've got the bone conduction headphones so you can still hear traffic or you're on the train or whatever If you're not following along with the things, that's okay. We're going to summarize at the end and wrap it up with a bow and make some nice points so you don't have to follow it exactly, but it really helps to follow these things exactly because honestly, it helps for me at least to think about the chemical process and the diagrams. It really helps for me at least. Anyway, where do we want to start in a cycle? because we should start with acetyl-CoA, but we kind of cannot because the cycle won't really make sense if we do, but anywhere we start in the cycle, like it's a cycle, so it just has to keep going because each step has to, you know, you know what I'm saying. So see, even the argument sounds circular. So where do we start? So overall, I would say don't worry about the names except for the first two things. And we already know the first thing, which is acetyl-CoA. So this is the two-carbon thing that gets made from both the breakdown of fat and the breakdown of glucose. So the second name we need to think about here is something called oxaloacetate. So one more time, oxaloacetate. This is a four-carbon molecule. But when oxaloacetate and acetyl-CoA combine, they become citrate. So this is the first step in our cycle. So each step is not really so much a molecule, so much as it is the process of what the molecule is doing. Does that kind of make sense? Instead of thinking about what we have in between, it's like what's happening in between that really matters. For sure. Yeah, yeah, yeah. So we're also going to talk about how long the chain is, because that's important to pay attention to, because we start with four and a two, which makes six, and then we have to get back to four, and that's also in part where CO2 comes from, and we saw that in the breakdown of glucose, you know, six carbons become three, then three become two, and so that's our first loss of CO2, and then we have two more CO2 lost in the cycle. So first the thing that we do with citrate is we rearrange it a little bit into an isomer called isocitrate. So it's very, you know, silly stuff, but it's the first thing that happens. So you're not going to do your thing on citrate. A thing happens, then you have isocitrate. And now this means, this rearrangement means some fun stuff can happen. So the first thing we do to isocitrate is we generate an NADH which is a reducing equivalent and a CO2, right? So now we're down to five carbons already. And so remember from the last episode how what's eventually happening to carbon is it's bonding. you know more and more to oxygen and so both citrate and isocitrate have three places where carbon has three out of four bonds to oxygen so it's very tantalizingly close for all three of these you know little chemical magic and we can just pluck off a CO2 and now we are left with alpha-ketoglutarate again forget the name but it's a five carbon chain like I said the one carbon on the end we're not gonna you know Go Through Which Carbon Is Which. We've kind of already done that a little bit, but it loses not only its bond to the carboxyl group, the one that the CO2 gets plucked off of, so this carbon that's left, but it also loses another hydrogen, and that means the oxygen that's left gets the double bond to it. And so now that places that carbon in danger of another chemical reaction. And so now alpha-ketoglutarate loses another Co2. And this generates another NADH. So now we are back to our four carbon chain. So it sounds simple that we've got, you know, we start with citrate, we do a little do-si-do, and then suddenly we can lose two CO2s and gain two NADHs really quickly. So that's cool, but we're not quite done. Because we can't just stick acetyl-CoA onto this thing yet, because we can actually get more energy out of alpha-ketoglutarate. And so what we do now is we actually reintroduce coenzyme A. So acetyl-CoA, this is where the CoA comes from, it's coenzyme A, which is one of those, you know, preparatory bonds that we kind of mentioned in, I think in the fat burning episode. And so this means we get succinyl-CoA. So from succinate. And now having this molecule is actually a big deal because we can generate GTP from it, which is guanosine triphosphate, which can easily be turned into ATP. So how cool is this that like in just a couple steps, we have generated two reducing equivalents, we've gotten rid of two CO2s, and we made an ATP. Like how cool is that? Yeah, also, if this sounds a little bit familiar from the fat metabolism episode as well, Doing a similar thing of working your way down this chain. You started with glucose, six carbons, and then you're just slowly popping off these carbons and some oxygen as well. But it definitely should feel similar, hopefully, for people. Yeah, that's actually a good way to think about it. It's like this is a long process of efficiently stripping electrons and protons and energy off of molecules. You know, you might notice we have an ATP. Is this where aerobic ATP comes from? The answer is, unfortunately, no, because we haven't seen an oxygen yet. But, you know, if you're keeping track at home from a glucose, we've generated a total of three ATP so far. But if we're coming from fat, this is our first ATP to be generated. So no oxygen yet, but it's coming. So now with the GTP generation, we lose the CoA, and now we just have succinate. loses two hydrogens and two electrons. So this is going to become fumarate. And now from fumarate, we actually have really easy stuff. So fumarate adds a water, which changes the carbon double bond into a, basically into, it hydrates it, making it malate. Or malate or malate? I'm never sure how people pronounce it. And what we notice about malate is... I say malate, I don't know. Yeah, okay, all right, I'll go with malate too. You know, it's chemically very similar to isocitrate, and a similar reaction occurs in which a proton gets taken in an electron, and so that yields an NADH, and that final step turns it into, drumroll please, oxaloacetate. And now we have concluded our Krebs cycle. So that wasn't too bad, was it? I don't think so. Hopefully people can follow along. Yeah, and that's a pretty chill version of it. If you got it in a biochem lecture like I did, it takes two full classes because we learn the mechanisms of the rearrangements and we learn all the names and the enzymes. Anyway, so to summarize all of this, a six-carbon chain gets converted down to four. And on the way it made one ATP slash GTP, generated two CO2, three NADH, and one FADH2. But not only that, but we did it in such a way that instead of having four carbons of waste or figuring out ways to get smaller carbon chains CO2 and protons and electrons on the way out, which actually chemically seems like it would probably be hard to do. Now we can just stack the enzymes in a circle in the mitochondria and just reuse the same couple enzymes and recycle four out of the six carbons and this can happen pretty quickly. You know, if you think I'm kidding about the enzymes being arranged in a circle, Google substrate channeling and learn about metabolons. The wiki articles are really short but it's actually one of the coolest things I've ever seen in biology. So, warning if you... Search that in Kugel Scholar. There's a lot of mathematical modeling and entropy talk. It's really cool stuff. But if you want to follow along, it's so worth it. All right. So where's oxygen in all this, Kyle? Like, what's the point of what we just did? Well, we'll see, hopefully. But yeah, I think we kind of hinted at this before, right? That sometimes, even if you're... Burning Fat or Sugar in an aerobic quote-unquote process, it doesn't actually require oxygen or what some people might call an aerobic process may not actually at first glance appear to require oxygen. Yeah. Yeah, and that's one of the funny things is that like, you know, I've... You know, I used to think that the Krebs cycle was also aerobic. I was like, oh yeah, it's aerobic metabolism. It's in the mitochondria, right? And it's like, no, there's actually a really cool thing about there being a disconnect between this and the other thing that we're about to talk about. So yeah, so we get like CO2, it's a waste product. We get one ATP, like, all right, whoopty shit, who cares? One ATP. Where do we get like the massive amounts of ATP that we... You know, can generate with oxygen. So here's the thing is we get four reducing equivalents. Remember that we generated an NADH and glycolysis and then ungenerated it when we made lactate, but lactate actually gets transported into the mitochondria and then NADH gets generated there. So it's, you know, kind of bypasses a separate NADH shuttle, which we don't have to talk about, but that gets used too. So what are all these reducing equivalents for? is the big question. Kyle, do you remember the name of this next thing? Is it the electron transport chain? It is, in fact. And actually, ironically, there are no other names for it. It's just the electron transport chain. So unlike the... That's nice. Yeah. Unlike the Krebs cycle, this has only one name. So the ETC, the etc. But this is not actually an etc. thing. This is like, this is the meat and potatoes. Well, it's like the meat. I think we just talked about the potatoes. Equally Harding. Potatoes, yeah, for sure. And so, and it does just that. It's very, very simple. It transports electrons. And so, you know, we've probably mentioned this before, but I really just wanted this on the podcast because I'm really trying to distill this stuff down into kind of how it works and the main takeaway. So even if you're not following the chemistry itself per se, that's all right. So this is actually, we're not going to get too into the chemistry here because actually a lot of it's still under investigation. There might be, you know, electron tunneling happening when things go from, you know, quinones and semi-quinones and, you know, all sorts of stuff that, you know, I leave to the real experts on, you know, these things. But anyway, so let's distill it to the most important parts. Where does the electron transport chain happen? because this is important because remember that structure and function in biology are very intertwined. So remember that mitochondria have two membranes, the outer and the inner. So this happens on the inner mitochondrial membrane and the innermost compartment of the mitochondria is where the Krebs cycle happens. And in a minute, we're going to see why the extra membrane is critical. So the electron transport chain has five enzymes involved in it. Well, really technically four. And there's two pathways for it to go. You can go one. So we're going to talk about the enzymes here, usually sometimes called complexes because they're complex of actual separate proteins. They bind together like Voltron and make a big one. Yeah, so we can go from... Enzymes 1 to 3 to 4, or also 2 to 3 to 4. And we're going to talk about, there's 5, but we'll talk about 5 in a second. The 1-3-4 pathway uses the NADH that we've been generating. And the 2-3-4 uses FADH2. And actually the cool thing about FADH2 in Complex 2 is that it's not like floating around really, it's like bound to the thing. So succinate actually, from the Krebs cycle, actually gets transported. right there into Complex II, which I think is really cool, actually. So both pathways involve taking protons and electrons from NADH and FADH2 and shuttling them through the electron transport chain. So what's the electron transport for? I mean, obviously transporting electrons, but like, why? What are we doing with this? We are pumping protons, right? Kyle, quick, you want to talk about pumping protons for a second? Well, hopefully people remember, so protons positively charged, electrons are negatively charged, protons are also sneakily called like hydrogen ions, even though it's like kind of confusing, but a hydrogen atom is just a proton and electron, so then if you strip away the electron to ionize it, you're just left with a, with a... Proton, and then in chemistry and in biology, it's very popular to write that as just H+, which is just a single proton. But protons are what, when in solution, if they're free protons flying around, that's how you acidify water or acidify a solution. And that's what we actually measure when we measure pH is the concentration or lack thereof of protons. Yeah. And so as electrons get transported down the chain, we actually pump Protons between the innermost mitochondrial compartment and the intermembrane compartment, so the one between the two membranes. So if you've seen a diagram of mitochondria, and I assume most people have at this point, you know, it looks like, you know, like a ribbon scrunchie kind of thing. And inside all of these, the cristae, as they're called, that's where all of this stuff happens, is on the cristae. That's where all of the... membrane proteins for the electron transport chain are bound. Like complex one will pump like four protons or something when an electron gets transported through it. So we're using the energy of the electron wanting to go to the end of the chain and binding with oxygen to make H2O. This energy gets used to pump protons from the inside of the matrix to between the two membranes. And this actually takes a good deal of energy because as we'll see in a second, we're actually Pumping these protons upstream. And they want to, you know, get back from entropy. And that's how we, spoiler alert, it's how we generate ATP. And so that's what happens is complex two doesn't actually pump protons. We'll probably talk about that more next episode. But this is the basics of it. And so pumping the protons between the two actually means You know, proton concentration is just pH, right? And so, or technically it's the log of the concentration, but so what's a normal pH in, you know, cells of the body? It's 7.4-ish. So what's the pH of the innermost space of the mitochondria where the protons are getting pumped out of it? It's 7.7. So it's more basic because we've had a bunch of protons pull out of it. What's the intermembrane space, pH, where the protons get pumped into? It's 6.8. It's acidic. So I think that's actually really, really cool. And there's almost like an order of magnitude of pH difference between the two sides of the membrane. Remember, pH is actually logarithmic, so it's a very, very large amount. and that means that the two sides want to equilibrate. So Kyle, talk about the equilibration potential to equilibrate. You're taking advantage of these two, basically if you have, you know, one side of this membrane is held at a, with more or fewer protons than the other side and so this actually creates a imbalance and Nature generally wants to sort of homogenize and create as much randomness or sort of even randomness as possible. And so ideally, the protons would be evenly distributed across the membrane. And so when you actually hold this, if somehow you could take a very tiny multimeter and measure the voltage difference between these two sides, you would actually find there's a slight voltage difference. Kind of how a battery works, right? Where you have, you know, more protons or in this case, in a battery's case, it's electrons that move around, but we'll forgive that for a second. And so actually, it's, you're, you have to do work, do some work, obviously, right? Because you're, you're, you're storing potential energy. In order to, you're storing potential energy, yeah. And, but then later you can cash this potential energy out to do something useful, like make ATP. Right, exactly. So you're, you're. You're, you know, classic Lisa in this house, we bail the law of thermodynamics. Energy is not created nor destroyed, but you're turning this energy that your body can't really use in this electric potential or this pH balance into something that your body can use, which is ATP. Right. And this happens in a very, very controlled manner through complex five, the fifth enzyme in the electron transport chain, which You know, again, I wish we could spend 20 episodes on it. There's so much cool stuff. Nerd. So protons actually do slowly leak back and forth between the mitochondrial membranes, you know, because it's nothing's like perfectly, you know, leak proof, especially with a molecule as small as a proton. But the leakage is generally controlled. And there's a lot of there's actually the regulation and control of. You know, the Krebs cycle and electron transport chain and the potential energy between the two pH differences. Like it's hugely complex and it's really cool. But anyway, that's besides the point. So the protons actually, for the most part, slowly, quote unquote, leak back from the, between the two, that goes from between the two membranes back into the innermost mitochondrial space through complex five. and this pressure exerted from the high pH side trying to get to the low pH side actually drives Complex 5 literally like a motor. Like, if you think about your crankshaft in a car, it's like that. At, like, max ATP synthesis rate, the motor spins at a rate of 130 revolutions per second, which is 7,800 RPM. You're up into, you're up into, like, turboprop, you know, like, territory here. It's like a, like a turbine engine instead, you know? Yeah, or like, like a GT... Yeah, GT350, like 8250, that's like a sky-high red line, like Ferraris, like 9000, like, oh my god, you know, that new Gordon Murray thing, like, what, 12000? Are you kidding me? You know, motorcycles, F1 cars, yada yada. So this is, you know, it's really fast, and it's happening in every cell of your body. You have these tiny little motors. Granted, it is. It is also really tiny, and it is also, you have to imagine, it's also not doing this in air, it's doing this... In your cells, so it's not like there's just air to spin through. It actually has to spin through, like, you know, water. Yeah, yeah, exactly. Yeah, so as the quote-unquote motor here spins with the pressure from the protons leaking back, it takes ADP and phosphate, and it regenerates ATP. It kind of, in a crude way, you could say it just shoves them together. Yeah. And so, you know, ATP's transfer of phosphates releases energy. So obviously it takes quite a bit of energy to stuff a phosphate back onto an ADP. And that's how we get aerobic energy. So remember, we're transporting electrons down the electron transport chain. We're pumping protons into the inner membrane space. And then we are slowly... Oh, and obviously when the electron transport gets done, the electrons and the protons... Turn Into Water. That's where the O2 comes from. Because oxygen, technically, if you look at the formula, it's like one half O2, and half an O2 really, really wants to become water. And so then once we get all the things pumped, we have this proton gradient, and the proton gradient wants to equilibrate, and so that comes through complex five, and that drives the motor, quote unquote motor, and that makes a... ATP. And so this is kind of, you know, this is how complex aerobic metabolism actually is. And, you know, if you've had biochem like me, it'll probably sound familiar and you'll go, oh yeah, that. But like... It's not like you just take a carbohydrate. How many episodes ago did we take a fat molecule? How many hours ago a fat molecule and a carbohydrate molecule and turn them into acetyl-CoA? And we've had to go through all of this to finally get to oxygen? Yeah. It also kind of is just a glimpse into how complex... your body is that you totally take it for granted and you think like oh like yeah I wake up in the morning and it's fine I'm like eating my food here I am eating my breakfast drinking my coffee or whatever but this was always a really cool thing that I liked about bio and biochem was like Seeing how complex these things are, you know, you think like, oh, I'm just burning sugar. Like, well, what does burning sugar actually mean? Like, it's not just lighting it on fire, you know? Like, your body, that would be bad. Like, this gives you a very controlled way, whereas, sure, if you took a bunch of sugar and dumped it into a fire, you'd get a lot of heat out really quickly, but that's not a really useful way for your body to use it. So you have to be a little more thoughtful. Yeah, that's literal combustion of sugar. And this also gets called combustion, especially in a lot of the older literature. But, you know, combustion is, you know, what's the chemical formula for combustion? It's still the same thing. It's like, you know... Oh, so yeah, combustion is just, right? Like, if you take hexane, hexane is also a six-carbon... molecule, and you can burn it, literally burn it, with a fire, and you get the same byproducts, you get carbon dioxide and water, which is what you get out of a six-carbon sugar, you get carbon dioxide and water, you just, that arrow that you draw, where it starts with six carbons on one side, and then an arrow across, in a fire, it's extremely rapid oxidation that causes the molecule to break down into carbon dioxide and water in here. Oxidation is happening, but that arrow isn't just like heat and or a spark in the presence of oxygen. It's like all of these processes that you've just covered up with this little arrow. Yeah, yeah, exactly. And that's, you know, that's what we started with a long time ago, or like at the top of this episode, top-ish. You know, C6H12O6 plus... Plus O2. Yeah, sorry. 6O2. I was reading the stoichiometry. Plus 6O2 yields 6O2 plus H2O. You know, that little arrow has a lot of context. Yeah. Yeah, so this entire illustration is meant to really show a couple things. So if you got a bit lost, we're sorry. I hope it was fun to listen to for a bit at least. So here are the key takeaways. First is that we break down fats and carbohydrates in long, complex processes to strip protons and electrons from them. That's the big goal, stripping protons and electrons so we can stuff them into the electron transport chain to aerobically generate ATP. These protons and electrons move down a path that generates water from oxygen, and this path creates a chemical gradient that dissipates through a specific channel, kind of like a river through a dam, like the Hoover Dam. You know, you can let the water through sometimes. And that energy from, you know, that quote-unquote pressure generates ATP. So a term like oxidative phosphorylation isn't just one thing, it's several. And, you know, depending on where you want to start from. If we start from carbs and fats, you know, it means breaking them down. Then it means the Krebs cycle and, you know, generating electron and proton carriers, reducing equivalents. And it means, you know, sending these... things to do their specific duties. Electrons go through the chain, they become water, and the protons get pumped out of one thing into another, and they eventually become, you know, well, they just stay protons, really. So there's a bunch of stuff going on here. And, you know, it's, you know, like you said, it's, you know, appreciating the complexity of the process. So when somebody says, oh, you're working aerobically, you really, really, really know what it means now. And, you know, again, we can think about all these things as coupled, you know, but they're not the same. So, you know, oxidative phosphorylation isn't, you know, it's like a coupled, you know, if we just look at the electron transport chain, oxidative phosphorylation, it means we're taking stuff that we generated elsewhere and putting that to work in specific manners. And this always blew my mind when I learned, like, okay, so what happens when you eat food? you know where does that food go like you eat I ate a burrito today for lunch and it weighed like a pound right you go to Chipotle the burrito weighs like a pound and I eat this burrito that weighs a pound what happens to actually all of that Mass. If I then went on a long bike ride or something like that and I burned all the calories off in this burrito, you actually just straight up exhaling out all of that burrito, not all, but a lot of that burrito, you actually just exhale out into the air as carbon dioxide and water and then you pee out some of the water too and obviously you pass some of the stuff that you don't exhale. I always thought that was really cool that you don't actually hang on to much of The actual weight of the food that you eat after you go exercise or whatever. You're like, oh, I generated energy, but you generate energy not – you think like, oh, how do I break down this food and generate energy out of it? But what you actually care about is the energy stored in those chemical bonds, it's not – Some people, you know, it's not the mass that really matters. It's the, it's like how those, how all those atoms are put together, not the atoms themselves. Right. Yeah, exactly. Because there's, you know, there's less energy in certain combinations than others. So we have one thing left to do in this episode. So we're going to bring it all back home now. So we can actually calculate approximately. How many ATP get generated by reducing equivalence? And these are approximate. There are still studies happening where... Because, you know, we can see that, you know, the generation of an NADH or an FADH2 does not necessarily equate to, like, you know, how much ATP do you generate when it spins? It's like, well, how many protons come through and how many electrons we need to pump here to, like, make this proton gradient? And, like, you know, the proton gradient is actually... Fairly well-regulated, but it's not precise. And so the stoichiometry is how much ATP we're going to get for how much carbohydrate or fat or yada yada, or NADH and FADH2, the electron carriers, these are not... Hard Numbers. And, you know, it'll change a little bit based on, you know, efficiency. Yeah, it's not a bank. And, you know, you can, you can, like, you know, disrupt a metabolon or metabolone. I've seen two different spellings, too, so I'm really not sure how to pronounce it. You can disrupt one of those and have a little more entropy energy to pay, and that's going to make you a little less efficient and stuff like that. It's little things that can add up. Like, efficiency is really, really complex. So here's the textbook things. that we can say. So that's my big asterisk on these things. I know it's more complex than 90% of you, 99% of you are really not concerned, but I do get emails from people like, oh, hey, this was a little off, and I love that, by the way. Thank you for those. So we can calculate approximately, again, asterisk, textbook, get generated by reducing equivalence. So it's two and a half for NADH, right? 2.5. You know, the average American family with however many .2 kids or something. A fraction of a children, yeah. Yeah, so just a couple arms and a couple legs or something. And it's 1.5 ATP for FADH2. So in total, about 30 ATP are generated aerobically by a molecule of glucose and four anaerobically. And for the average molecule of fat, like a palmitate, I googled this, so if I saw the wrong number, I'm sorry, because fats have different carbon-length chains, and so you can actually get different numbers of reducing equivalents. So the chain length determines how much energy you get out of it. Now that seems obvious, but if I'd said it to you before, maybe it wouldn't have been, because it wasn't to me. So when you burn a molecule like palmitate, which is... the average go-to like middle of the road, you know, longish chain fat, you get 102 ATP out of it. Not 34 from a carbohydrate molecule, but 102 out of this fat molecule. And if you get a longer chain, you can get more fat than that or more ATP than that. So the benefit, it's like, why would we burn carbohydrates at all? The benefit is that A molecule of glucose generating 2-ATP in the cytosol happens really, really, really fast. And the 2-ATP in the Krebs cycle, slower, obviously. And a molecule of fat generates 2-ATP in the Krebs cycle, also slow. But the very slow version is the ATP generated by the electron transport chain with reducing equivalence because, as we've mentioned before, oxygen is the limiter here. And as Kyle has astutely mentioned, probably on the podcast, if my memory serves, or maybe we're just chatting, whatever. You know, you had said this is why oxygen vector doping works. You increase the oxygen delivered and immediately you can produce more ATP. You can have more energy aerobically. Yeah, absolutely. Like if you, you know, if you weren't able, if you were always able to keep up with the aerobic demands of your body, then the limiting would be like how quickly can you eat food or how much. How much fat can your body store? And rarely on a ride does your body run out of fat. Rarely. Never on a ride does your body ever run out of fat. Even after you bonk. Yeah. You're doing the Christian Bale from The Machinist and then going on a bike ride. No, and it's interesting because I think it's interesting because you're like, oh. I had to evolve, not I personally, but my, my, our, our ancestors, you know, evolved this very, very complex process to use this oxygen, like the, you know, ancient, ancient humanoids were around and in a oxygen, in an oxygen rich environment, and so you have to evolve some way to use this very oxygen rich environment, and it turns out nitrogen isn't nearly as reactive of an atom as oxygen is. So even though it would be nice to use the 78% nitrogen or whatever that we have in the atmosphere, we wouldn't be able to get as much work done molecule for molecule. Yeah. Well, actually, well, I think anybody working in explosives would tell you that nitrogens have plenty of energy in them if they're not N2. Yeah, yeah, yeah. All right. So overall, let's look at percentages here. The full oxidation of a carbohydrate. So if we get about four out of our 34 ATP generated anaerobically and 30 generated aerobically, we have 11.7 of our energy generated, quote unquote, anaerobically. So that's the two ATP from the cytosol and the two from the Krebs cycle. Full Oxidation of Fat is, like, let's say, palmitate, as our example, is 2 out of 102, which is 1.9% anaerobic. But, you know, they're a different length of fat, so that number's going to change, yada, yada. And, you know, we're not even looking at proteins here. So anyway, so what does all this mean in terms of what aerobic and anaerobic is? So first, let's talk about that the process has a maximal rate, and it has an upper limit. to function somewhat sustainably. And so trick question. That's not a trick. It's one of those things where like the teacher asks in class and nobody says anything because the answer is so obvious. It's like, this is a trick. So what three letters might represent this state? Anyone? Bueller. Bueller. No. It's everyone's favorite three-letter acronym from cycling training, or not acronym, three-letter abbreviation from cycling training. No, acronym works, I think. Yeah, it's ATP. It's FTP. The ATP and FTP, and the TP and ATP and FTP are not related. As nice as that would be, they are not related. ATP, aspirational threshold power. Oh my, yeah, just asking my aspirational threshold. 500, 600, do I hear 700 watts? All right, so anyway, so that's what this is. The process of aerobically burning down fats and carbs is FTP. That's your maximal rate because once you start getting over that... Your energy demand is higher than you can aerobically sustain. And you can extract a little more oxygen. If you look at ATP versus VO2 max, obviously we have a little more to go before we get to our maximum O2 supply rate. But if we're going over FTP, our energy demand is... High Enough that we can really, really, really churn through some glycogen. Like, oh my God, can we ever. And that's when lactate starts to build up quickly, which means we're over MLSS and yada, yada, yada. And so let's also remember the other very important point here is that both carbohydrates and fats get oxidized aerobically, and by the way, so is lactate, but always indirectly, indirectly. by the reducing equivalence going to the electron transport chain to make water and supply the proton pump, proton gradient. Also remember that the Krebs cycle and the electron transport chain give zero shits about where the acetyl-CoA or the NADH and FADH2 came from, as far as I know. So, you know, the Krebs cycle, the electron transport chain, they really mostly just care that they just... get enough to operate and keep supplying the body with energy. Otherwise, we are going to die, and that is a very sad day. Oh, as you say, it kind of reminds me of the way that the mRNA vaccines work in that you just trick your cells. Like, your cells don't care. If they encounter a piece of RNA, they're going to like, oh, I'm going to read this, and I'm going to make this protein. And, like, they don't... There's no way for them to know that, oh, no, no, no, this is a clever ruse that we injected this piece of RNA in for you little ribosomes to process. And similarly, there's no way for your body to know where the acetyl-CoA is coming from. right like it's not like this one is painted red no no no like you can't you know you can't paint or or somehow they're they're identical molecules they're indistinguishable right uh a single molecule of acetyl-CoA out of uh dog looks exactly like uh a molecule of acetyl-CoA out of a dinosaur if you could somehow get one yeah uh how about a chicken yeah there you go um delicious dinosaur Kentucky Fried Dinosaur Dinosaur nuggets. Oh, yeah. So I think the last point, the big important points that I want to make here is don't ever again let somebody say that burning fats is aerobic and burning carbs is anaerobic. That's really just the bottom line. Like, you do want to burn less carbs, you know, in your endurance endeavors so that way when you need to, like, sprint or whatever, you have more left so you could produce more power, yada, yada, yada. The whole thing that... You know, that's pretty standard stuff. So remember, the entire process is anaerobic until well after there's no distinction between a carbohydrate and a fat. I think it's really interesting, too, because people will think that, oh, if I, you know, oh, does eating more fat or eating less fat or more carbs or less carbs make me a better aerobic rider? And you're like, uh. Actually, don't spoil it, but that is one of the things that we're going to get to in future Wattstock episodes is talking about just that. We'll probably talk about the nature of aerobic signaling and adaptation and stuff like that. I really want to do some deep dives on that, just mostly because I get an excuse to hang out and nerd out all the time. So I think one of the things that we've also set up here for the next episode... We're far from done. Now we get to start applying this stuff. The thing that we've set up here is a conflict of acetyl-CoA. So next episode, we're actually going to talk about why... Why on earth does this happen? At higher exercise intensities, we don't burn as much fat. And at some point, we actually stop burning it altogether, despite the fact that, you know, the aerobic process is happening. So we're going to talk about that. I want to thank everybody for listening to the podcast. Please subscribe and share the podcast. That's the biggest thing you can do if you want to support us. But you can also support us if you want to buy us a coffee or a burrito, now that burrito places are open again, and I can go eat to my hearts and my... Literally my heart's content until I have a heart attack. So you can support the podcast monetarily at empiricalcycling.com slash donate. We have show notes up on the website at empiricalcycling.com. We have merch at empiricalcyclingpodcast.threadless.com. I'm still offering a free consultation, one to two hours, if somebody decks out their bathroom with empirical cycling stuff. Not worth it. For all coaching and consultation inquiries, questions and comments, just email empiricalcycling at gmail.com and don't forget Instagram AMAs on the weekends at Empirical Cycling and this weekend I'll be hanging out at Rooted and so that's going to be fun up here in Vermont and Yeah, so I'll be Instagramming from the feed zone or, oh, there's no feed zone, from just wherever. So, everybody, thanks for listening. Thank you.