Welcome to the Empirical Cycling Podcast. I'm your host, Kolie Moore. Join us always by my co-host, Kyle Helson. And I want to thank everybody for listening and ask that you subscribe to the podcast if you have not yet already and also share it with a friend or share it on a forum if you think that we've got the answer to somebody's question. We'd really appreciate when we see that and we would love to see more. Also giving us a five-star iTunes rating if we may be so bold as to request five stars. Also remember that we're an ad-free podcast, so if you'd like to donate to the podcast, thank you so much everybody who's donated. the last couple months, by the way, your support really helps. You can do so at empiricalcycling.com slash donate. We also have the show notes up on the website, empiricalcycling.com. We've got merch at empiricalcyclingpodcast.threadless.com. And if you have any coaching and consultation inquiries and questions or comments, you can email empiricalcycling at gmail.com. Also on Instagram, we are doing weekend AMAs in the Instagram stories. So give me a follow over at empiricalcycling in case you couldn't have guessed that and you want to participate in that. We've got lots of good questions and probably get a 30 to, no, 40, about 40 to 50 questions, you know, per weekend, which is awesome. Really, really good questions. So thank you everybody for participating in that. It's a lot of fun. So last episode was about repeated sprints. And I tried, you know, poorly in hindsight to draw parallels between adaptations to endurance training and repeated sprint training. So it's a complex topic that deserves a lot more time and breakdown. So I found an opportunity to do that today with the paper that we're going to be talking about. And I've been really wanting to do this paper on the podcast for a long time. And I'm really excited that, you know, finally going to be able to get into it because... It's a great, great scientific paper in terms of the – well, you'll see. So last episode was actually kind of an attempt to combine a 10-minute tips type episode with a real like Wattstock episode. And so what we're going to do is actually we're going to expand the 10-minute tips timeframe because I've been trying to, you know, oh, this would be good 10-minute tips. You know, then it's like, oh, we can't do that in 10 minutes. All right, so let's try to work it in. So we're going to expand that and kind of keep 10-minute tips as something practical and the Wostok stuff as the real nitty-gritty. 10 minutes, you know, is more like a suggestion sometimes. Now that we know what the rule is, we can bend it and break it, yeah. All right, so this episode, we're going to look at a study that looks at one of many components. of aerobic adaptation that we alluded to in the last episode and probably several other episodes. So before we actually get into the next series on metabolism that I'm really stoked about, let's get into this one. So Kyle, give me your thoughts on aerobic adaptation in general. Is it like a black box in mystery or does it seem kind of more accessible in some ways? I think for astute listeners of the show, hopefully they have heard, especially the series we did about VO2 Max kind of pulled back the cover hopefully a little bit on what aerobic adaptations are or what they can be. I think if you come into a discussion about aerobic adaptation, just sort of dissecting what people usually talk about in popular science discussions on exercise or fitness. You can maybe deduce that, oh, something about maybe I'm using oxygen better or I'm using oxygen more efficiently or I'm using more oxygen because people talk about VO2. And then you think about usually somewhere in there about burning fats versus carbs. Maybe you've read one too many gym posters and you think there's something called like the fat burning zone or whatever. Yeah, I think there's a range of places you could expect people to be, but generally think that, oh, if I'm more aerobically fit, I can do more work for longer periods of time, and I can do so using aerobic... Well, I won't say metabolism because I kind of get ahead of ourselves, but I can do so using aerobic means. I'm not going, quote, anaerobic. I'm not, you know, sprinting until I pass out or something like that. I'm able to keep going, so that means I'm working aerobically, right? Well, one would think, but that's actually one of the reasons that I want to get into the next series because we are actually going to explain what aerobic really means and the different pathways of metabolism. you know a little more of the nuance that I'm always trying to allude to and I always have a bad time explaining succinctly you know especially when I'm for instance arguing with somebody on a forum about something and there's there's a lot of you know this is one of those things where I think some people don't like what I'm about to say because it implies they're wrong but I don't mean you if you understand this kind of stuff, but I think a lot of people actually have some misconceptions about what aerobic metabolism really means. And that's why I'm really excited to get into today's paper because we're actually going to start to pull back the curtain on aerobic metabolism in muscles because we, with the VO2Max series, talked about aerobic metabolism in terms of cardiac and hematological, is that a word? Cardiovascular adaptations. And so today, we're going to be breaking down a paper that really looks at one of the mechanisms that causes aerobic adaptation, and we're going to talk about that. So here's some background info. Aerobic adaptations can be broken down into central and peripheral components. So VO2 max, the heart, that's central. Muscles, that's peripheral. Include also besides the heart, the vasculature, and we covered a good bit of that in the VO2max series. Examples, for instance, are stroke and plasma volumes, contributions to VO2max and oxygen transport. So again, refer to Wattstock 18 through 24, I believe. Peripheral adaptations are what happens specifically in skeletal muscle, ignoring neural things for now, and it's got a little different definition of central and peripheral. And we covered a little bit in Wastock number 20, you know, adaptation examples are like glycogen storage, mitochondrial density, increased enzymes and stuff like that. So how do we like actually achieve these adaptations? Well, again, with the central stuff, we did a podcast on Vida2Max. We didn't cover everything, obviously, but we covered quite a good bit. So how do we achieve peripheral, that is to say, muscle-specific adaptations? So this is an area of a lot of research, but let's go over a couple things that we do know about muscle. Generally speaking, most training types will turn 2X fibers to 2A, whether it's endurance training or heavy lifting, although it doesn't seem actually so much with lighter and faster lifting or plyometrics, so that's something interesting to think about, and we'll talk about that in a little bit. And as discussed in brief last episode, contractions are typically necessary to quote-unquote train a muscle fiber. So when we contract a muscle, an action potential comes down the nerve and enters specific channels in muscles called the T-tubule system. T-tubule because they're transverse tubules. So if you're going along the membrane of a muscle fiber, It looks like, it's like holes. It's like Swiss cheese. They're like a lot of like little exhaust ports in the Death Star, if you will. And they're holes in what's called the sarcolemma. So sarcolemma is the fancy way to say muscle cell membrane. So the membrane is dotted with these and they go really deep into the cell. So the T-tubules have around them the sarcoplasmic reticulum. Inside the muscle itself. So this thing goes down into the muscle cell and it's right next to the sarcoplasma verticulum. And this allows us to contract a muscle cell really quickly instead of, for instance, sending a signal to the surface and waiting for the signal to dissipate into the muscle cell. So the signal actually travels very quickly down the T-tubule and activates. the sarcoplasmic reticulum in muscle cells. And so the SR in muscle cells is actually an extension of what we all learned in high school bio of the smooth endoplasmic reticulum. So just a quick refresher on that, the endoplasmic reticulum is actually continuous with the nuclear membrane. It's part of protein and lipid synthesis and vesicles and other things like that. So in muscle cells, the sarcoplasmic reticulum, which is the smooth ER not the quote unquote rough ER that has embedded ribosomes the sarcoplasmic reticulum is actually brimming with calcium so just a note on the literature if anybody's out there reading it modern terminology is actually moving towards calling the sarcoplasmic reticulum the smooth endoplasmic reticulum just specifying that it's in a muscle cell you know because sarcoplasmic reticulum makes it sound like it only has a certain function. It has many. But we're going to keep up with the SR or sarcoplasmic reticulum for this episode. And so the T-tubules, where the action potential from a nerve signal travels down into the cell, are linked to the sarcoplasmic reticulum, which surrounds it, and they're linked by way of voltage sensors that connect to what are called reanodyne receptors. I have not actually looked too hard into this, but one reference says that every other reanodyne receptor is actually connected to a voltage sensor. So I think that for people who have maybe heard of reanodyne receptors, they're thinking like, oh, like, what is, what is it, it's supposed to, it's supposed to detect something, it must be detecting something, receptor, right? Detecting reanodyne. Reanodyne, right? Isn't that, isn't that what it is? Or not? Because We just talked about how it's a voltage sensor. It's connected to voltage sensors. Voltage, yeah. Or every other one, apparently. Every other one is. Yeah. Yeah, so they're actually really, really cool. And we're going to talk a lot about ranodyne receptors in this episode. Because ranodyne receptors in certain types of training, in certain situations, are very much linked through a short signal chain to aerobic adaptation. Let's talk about them for a second. So when ranodyne receptors get a signal, and it's a little different between skeletal muscle and heart and the other places that ranodyne receptors are, they spill calcium into the muscle cell. They release it. Remember the diffusion thing on oxygen, how oxygen diffuses passively into the cell? Calcium diffuses passively into the muscle cell when the ranodyne receptor opens because there's such a large... Concentration Gradient Difference that naturally the entropy is just going to go and there it is. So why is it called a reanodyne receptor? Is there like a reanodyne neurotransmitter or something like that? No. And if you had any in you, it'd probably be bad because it actually inhibits calcium release. Ranodyne is a poison from some plant or other, and it has a very, very high affinity for one conformation of the ranodyne receptor. And it was actually originally used in the lab to isolate the ranodyne receptor, hence the name. So this is one of those unfortunate things in science where something gets named for a poison because it has high specificity before it actually got its name. or, you know, before people knew maybe what its function was, potentially. So ranodyne receptors can also sense, in addition to, you know, being activated by the voltage sensor to release calcium, they can also sense calcium in the muscle cell, and this can cause a feed-forward loop releasing more calcium, but they'll actually shut when the cytosol calcium gets high enough. to prevent the total and complete emptying of the sarcoplasmic reticulum. So how cool is that? Yeah, so that's really cool. So you have like a system where your brain and your nerves are going to send little electrical pulses down into your muscles and those little electrical pulses are actually going to cause your muscle cells to dump. Calcium, or have calcium ions dumped into them, and then this is how your muscles actually work. Yeah, this is exactly it. This is work to, like, contract. Yeah, yeah, right? Like, you have these little electrical pulses from your brain, which... Yeah, it's really just electrolytes like sodium, you know, going through a membrane and changing the voltage potential of the membrane. That's how that signal travels. So this is why all those... Sports drinks want me to drink calcium and sodium and stuff. Among other things, yeah. Well, a better absorption and blah, blah, blah, but we'll get into that very much another time. We have other things on the menu for now. The calcium presence in the cell has a lot of effects. And if you're not familiar with the mechanism of muscle contraction, it is actually because the calcium binds... to a protein that wraps around one of the components of a sarcomere, which is the things that actually do the contracting. And when it binds to this, it actually pulls the protein away from the binding site for the myosin, and that is actually what allows the contraction to happen. So that's why calcium is important, and that's why calcium is going to actually cause a contraction. Calcium presence. Causing a contraction is really, really critical here because it has other effects in a cell that signal the need for aerobic metabolism. So let's think about this for a minute. The presence of calcium means contraction, and that means ATP utilization and energy demand. It's pretty obvious that if there's sustained presence of calcium, then there's a sustained energy demand. If calcium's the first sign, literally is the first sign of energy demand besides the action potential, it makes sense that calcium can switch things on to anticipate metabolic need of ATP. So instead of like your body being able to just somehow magically measure the amount of ATP that you're burning through, it's measuring the fact or it's responding to the fact that there is this increased concentration of calcium that isn't normally present when you're like sitting on the couch like eating donuts. Oh yeah, definitely. And if you want to listen to 10-minute tips number six... On ATP and disequilibrium, that gets into how critical it is to maintain a certain ATP ratio in cells, you know, away from AMP and ADP. And we actually have several mechanisms that are really cool in our cells to maintain that ratio as high as possible, and we'll probably get into that a little bit in the next series, so look forward to that. I certainly do. But all of this means that calcium in a cell... can also be a signal itself for aerobic adaptation. So let's think about calcium in the cell. We're not going to get too technical here, so I apologize for kind of glossing over some of this, but some of the signal chains here just get really ridiculous. Calcium accumulates in mitochondria, and it actually activates certain dehydrogenases in the Krebs cycle, and it has a lot of other effects that we actually may or may not fully understand yet. Calcium also activates CAMK2. I don't know if there's actually another pronunciation for this thing. It's calcium calmodulin kinase, which can do things like modify cell response to handling the increased calcium or, for instance, increasing glucose uptake. Or this can upregulate paroxysome proliferator activated receptor gamma coactivator 1 alpha, PGC1 alpha transcription. Our familiar nodal regulator of mitochondrial biogenesis. So, yeah. So, more calcium or higher concentrations of calcium are going to tell, signal to your cells that they actually need to make some of these mitochondria. Potentially, but having a high... Calcium concentration in your cell would be bad because it means it's going, for a long time, it means it's going to be contracting constantly and that's going to be a huge ATP demand and that's bad. And so the cell only wants calcium in the muscle cell causing contractions as only when necessary. So it's going to actually mop up those calcium ions when possible, right? And so this calcium is actually a fairly common signal associated with obviously muscular contraction and ATP and reducing equivalent demands. And it can act directly on DNA as transcriptional co-regulators. I mean, PGC1 alpha, not calcium. Reactive oxygen species, and we'll talk about why we're mentioning this here in a minute, can have a similar effect here as we'll discuss. So because oftentimes when you see calcium, we see oxygen. And so one day we actually may do a series on how all of these aerobic pathways work and really get into the nitty-gritty of aerobic adaptation and stuff like that. PGC-1 Alpha can also be activated by things like Cold, AMP-K, P38, Map-K, but for now the important thing is just knowing that stimulus leads to aerobic adaptation is probably a good place to start for now. So, oh yeah, sorry, go ahead. Also, for people who are interested in this in another way, this is not the only way that calcium is used as a signaling mechanism in your body. Like you can look up, there are like dozens of different like types or like a dozen different types of like calcium channels where your body will use calcium to do all sorts of other things, which is kind of cool. Oh yeah, definitely. You think like, oh, this stuff that your teeth or bones are made out of, also very important for the rest of the functioning of your body, like controlling your blood pressure. Yeah, I mean, well, Kyle, you were pre-med, so you actually know more about that than I do. Yeah, one of the classes of medications that give people who have high blood pressure, some people have probably heard of something called beta blockers, but calcium channel blockers are another medication that people will take daily to reduce high blood pressure. Oh, okay, cool. All right, so I think that's probably enough background information to get into today's paper. So the title of this paper... I'm sure some of you have probably guessed it by now. Ranodyne receptor fragmentation and sarcoplasmic reticulum calcium leak after one session of high-intensity interval exercise. So put that on your bingo card if you had it. Drink. So Kyle, can you take a wild guess at what they found based on the title? I'm going to guess that high-intensity intervals cause calcium. to leak into cells maybe more so than they may have estimated at their outset or maybe more so than other forms of exercise. Okay. You're actually pretty close. So, you know, the actual premise of this paper is funny because in the intro they were talking about they were looking for a quote-unquote minimum dose for HIT given the wide support for its efficacy in the literature. Asterisk. We'll get to that in a little while. Especially on short of time durations that happen with traditional endurance training. So HIT seems to increase VO2 max better or as much as longer aerobic sessions. So at the time of this paper's publishing in 2015, Exactly how high-intensity training triggered aerobic adaptations like mitochondrial biogenesis was more or less unknown, as far as I know. There may have been some other papers that I'm not aware of, probably were, so I'm sorry if you know of another paper like, oh, it was this one! But this really attempts to uncover it, and I love the way that they went through this, and you'll see why. So the definition of HIT, obviously... The paper we're looking at uses HIT as high-intensity interval training, and by this it means a certain type of interval training that can sometimes get called sprint interval training or SIT or probably several other things, and some people might think of HIT as different types of intervals than this one, and obviously some researchers and coaches and other people have different terminology, or some people just use it as a catch-all term and have specific names for it. different names in each interval type. I actually have several books on HIT stuff that uses very different names. So my apologies for all that confusion here. We're just going to go with the paper's terminology. That's interesting. I think for most people out there, they're thinking like, why do I know about high-intensity interval training? And that's probably because people may or may not have heard of Tabata's. And this paper actually came out, looks like, about 20 years after the original Tabata paper. And Tabata, for people who are aren't familiar is that sort of infamous protocol of 20 seconds more or less all out and 10 seconds rest repeated for four minutes straight and so people have probably seen this or maybe even they've done this maybe or similar sort of structured type workouts and that's probably the most maybe the most famous I think it might be yeah actually remember we did I think it was episode two or three on or four on how high-intensity interval training makes you faster. And we actually looked at the original Tabata paper, if I'm not mistaken. I could be. We looked at it at some point in the podcast. Yeah, it was Wattstock number four that we made, that we looked at high-intensity interval training. Yeah. And so, I mean, he was actually looking for a way to increase anaerobic capacity, and he found an increase in VO2 max, which I thought was really, really cool. And to me, that's what... HIT stuff is short, intermittent stuff for the most part. Also, because the title of this episode, how high-intensity interval training may not make you faster, I deliberately chose that to contrast with the previous one because we had alluded to that, I think, in that episode later on, how sometimes doing HIT stuff for various other reasons than the oxygen debt and deficit ones we looked at in that episode. Well, we're going to get into all that right now, actually. So it can have some efficacies, it can have some not-efficacy, and it can have a lot of different mechanisms of adaptation. So here's, well, let's get into this paper and we'll discuss the actual protocol they use because they use 30-second max intervals. I think actually Tabata might have used like 167% of VO2 max power or something like that. Yeah, that sounds right. Yeah, like 100, yeah. Okay, so yeah, so hard stuff. Not totally maximal, but these intervals are maximal. And so this study here is actually a series of experiments. And they report on each experiment through the paper. And that's one of the coolest things is you can really see the logic chain going through it. and we can also see the results of one experiment influence how they set up the next one which is actually unusual to see in papers like this and also usually because people want to get as many publications as possible out so they'll write as many papers as possible for one experiment then they'll do the next one or write papers or potentially they will but I love this one. They started with 10 recreationally active men, and they did 3x30 second all-out efforts on a bike with 4-minute rests. To measure fatigue, they looked at force decrease in a maximal knee extension. So, you know, sitting there like a knee extension machine in the gym, so they did both voluntary, so maximal voluntary contraction where they had the subject try to contract their quads as hard as possible. and Involuntary, where they put electrodes on the muscles and they run voltage through at different frequencies. And for the sake of simplicity, we're going to actually ignore this. But they found that the electrically stimulated force was plenty decreased after three by 30 minutes immediately after and was actually not fully recovered 24 hours later. And so the electrical stimulation is one of those things where, you know, if there's any central fatigue, your nervous system isn't quite getting the signal out, and your legs might actually still have it, electrical pulses will actually make them contract maximally, or so we think. If anyone's ever used one of those, like, complex things, those e-stim, the, like, muscle stim-type devices, that's kind of like it, yeah. Just crank the voltage. You can actually get some surprisingly hard contractions out of this tiny little smaller-than-smartphone device where you're like, oh, wow, this is actually kind of impressive. If you look at the specifications, it's only running milliamps through the electrodes. It's not even shocking you with as much voltage as a USB output. But okay, so but just to be sure in the next experiment and in the subsequent ones, they went with six by 30 second all out efforts with four minute rests. It sounds really hard. Yes. It's like not fun at all. Yes. Okay, so again with 10 recreational subjects. Oh, if anybody's wondering, four minute rests, I do not consider actually full rest after these types of intervals. Yeah, like 40-minute rests might be. Yeah. Well, for you and me, sure. But for most athletes, if I give somebody like four-minute rests, I'm not expecting them to be fully recovered for the next effort. And that would be the point of those intervals. We'll get into why. It may be probably another time. Definitely another time. Okay. In the next experiment, they did with 10 recreational subjects. They also took vastus lateralis muscle biopsies at 10 minutes and 24 hours post-exercise. That's one of the muscles in the quad. I forget which one. Outer. It's the outer one? Yeah, lateralis, medialis. Medialis is the inner one. And, okay, so at 10 minutes post-HIT training, No changes were detected, but at 24 hours post-HIT, no changes in what, you ask? Okay. Only 15% of reanodyne receptors were the entire whole-sized monomer. The other 85% were fragmented. Hmm. So are they fragmented in a... Repairable way? Or do you have to... One would presume, and we'll talk about that in a little bit, actually. But the short answer is they ran a gel and they found instead of one band, they found three. Ah. So actually doing these all-out intervals actually through some mechanism ended up kind of... Breaking these reanidine receptors. Yes, and the paper actually suggests a mechanism, and we'll talk about that in a little bit. So, for instance, other things associated with calcium handling besides reanidine receptors, which obviously release it by voltage, and, you know, calcium feed forward, blah, blah, blah. So, things that actually have to do with voltage detection, like structure, like DHP and SCRCA, calcicequestion, actin, dystrophin, they actually showed no change at all. So it actually seems like the ranodyne receptor is a particular target here. And for comparison, they had eight recreationally active people run a marathon on a treadmill. So I'm so sorry for those folks who have not trained for that. Really annoying. Just agonizing. Yeah. So they wanted to find out if the lower intensity, both absolute and relative, because, you know, marathons are still hard. Did it cause the same fragmentation? It turns out it does not cause reanodyne receptor fragmentation in this case, not at one hour post or 24 hours post-marathon, but it did cause dissociation from a stabilizing protein, which is actually consistent with a well-confirmed finding that These types of exercise can indeed cause some calcium leak. So you don't actually have to, you know, cleave the ranodon receptor to get some calcium leak. But in some subjects, it was much, much more prevalent than in others. So we've actually got the link to the paper in the show notes. It is open text, and they have a supplemental PDF with it. And if you go down to figure S4B, you will actually see what I'm talking about here. So a lot of the other papers that they referenced on this, by the way, have the word leaky in their titles, which amuses me so much. Yeah. Yeah, and so if you want to head to that paper in the show notes, you can go down there and check out all the references. I skimmed a couple. I didn't really get into them. Okay, so this paper also looked at another way to confirm that there was some calcium leak in these subjects. So we mentioned briefly in the last podcast that fatigue has a lot of facets and handling calcium is actually one of them. So calcium leak is associated with the fatigue. Knee extension max voluntary force was down by 40% at five minutes after the six by 30 and not surprising really since the power output. of the efforts actually went down an average of 25% through the 30-second bouts. But they found that there was not any decrease in the central activation or what we've discussed previously as neural drive, and you can refer to Wattstock number nine for that. So looking at the biopsied muscle fibers themselves, there didn't actually seem to be any associated dysfunction. you know note well that these were skin fibers if you're familiar with these types of experiments which have some drawbacks but I'm not sure any of them actually apply in this case. So in other words what they did was they looked at the sequence of events in brain to contraction signal chain and they narrowed down the culprit of dysfunctional calcium release by the sarcoplasmic reticulum. Brain's fine. The signal transduction is fine. When it gets to the calcium stuff, that's not quite so good. But if we electrically stimulate, we can do this. And if we actually look at the structure under a microscope and make sure that all of the structure of a sarcomere is intact, they found that everything's fine there and that they were actually operating fine. This is all, despite the fact... that in the immunoprecipitation block they provided for the 6x30 second experiment, there's no obvious fragmentation of the ranodyne receptor immediately, but there is the fatigue. Hmm. So that's interesting. So you get to the point at the end of these intervals, and it kind of makes me think of that sensation you have when you do hard intervals all out where you don't have full recovery in between, where you get to a point where you just Basically just blow up, right? And you can't pedal any harder, even though you think you're like telling your legs to pedal, but it just like, you know, your legs feel tight, you know, you feel like you got a little bit of a pump or something, and then you're just like trying to pedal and you can't. Even though you feel like your mind is telling your legs just as hard as you think you normally do to pedal and you get nothing out of it. Yeah, or as hard as you can and nothing happens. Nothing happened. And you're just like, you're pedaling there and you're like, I'm doing, I feel like I'm going all out and I'm doing like 90 watts or whatever because you like, you like blew up on a climb or you, you, you were sprinting and then you, you know, you died or something like that. And that's, that's kind of like what makes me, what this makes me think of is that sensation of, I thought I'm telling my body to do something, but the muscle, it feels like your legs, your muscles are just like unwilling to participate. Yeah. And it sounds like from here that that's what's happening where your brain is firing and there's neural drives still occurring. You can measure the electrical signals that your brain and your nerves are sending, but your muscle cells are unwilling to cooperate. Yeah. And then if you take those same fibers after, you know, the 6x30 and you make them contract, which is I think what these scientists did by putting, you know, some Calcium in there and saying, okay, you guys can track now, but taking out the Rhianodion receptor from the equation, they work fine. Yeah. Yeah, so the Rhianodion receptor fragmentation may or may not be a contributor to the mechanism of fatigue in the muscles, but obviously there are other mechanisms of fatigue at play. And you wouldn't necessarily be able to feel that, right? Like, you couldn't, you don't have, like, nerve endings in your rheanodine receptors to feel them, like, break apart. So it wouldn't necessarily feel painful or something like that for this fragmentation to occur. Yeah, exactly. And it's also not to say that other things are not happening when you get to that fatigue point. when you're trying to pedal really hard and nothing's happening. Certainly, there are a lot of experiments that show that a lot of other stuff is happening. Increased presence of inorganic phosphate is a big one. That actually might make its way into the sarcoplasmic reticulum and have all sorts of problems. So there is a lot of stuff in there. And it's not just this, but... So it's not lactic acid. Please, for the love of God. No. Okay, sorry. Well, so this actually brings us to our next experiment on 14 elite cyclists and runners. So they did six by 30 seconds all out cycling with four minute rests, same as previous groups. And they also saw the prolonged forced depression, the fatigue in the maximal voluntary contractions and electrically stimulated knee extensions. However, there was no reanodyne receptor fragmentation 24 hours later. Interesting. So therefore, the fatigue that they experienced is probably not intrinsically linked to this fragmentation, although there's a lot of other potential reasons, including glycogen depletion and other stuff, blah, blah, blah. Hmm. Interesting. So there's something that elite cyclists and runners, something about their, the difference between them being recreational active and elite that is going to prevent or stop this fragmentation. Yes, actually, we're going to get to that in a little bit, and I'm so excited for that. Well, actually, we're going to get to that right now. So there is one very interesting difference between the well-trained and the recreational athletes here. Two things they measured called superoxide dismutase and catalase. These are enzymes that are meant to deal with free radicals in the cell. So there's no need to freak out about free radicals in your cells. They're there all the time. Free radicals due to exercise, and this is not pathologic conditions, which also happens and are obviously a big concern. Due to exercise, they're normal. Listen to Wasp stock number 13 for more info on that. and what this paper does mention that I don't think we did in that episode is that complexes one and three are probably where a lot of these radicals come from and we'll be talking about that in more depth at some point soon but anyway more oxidative respiration equals more free radicals no matter what the same way that if there's flux through glycolysis we make lactate except we make a lot more lactate to pyruvate than we make Free Radicals to Water, for instance. So this paper actually found that the trained athletes had at least twice as much superoxide dismutase and catalase as the recreationally active men. Oh. Yeah. So endurance training in general increases your natural antioxidant capacity of muscle, hence the doubling of the trained men. Which I would expect to lessen these subsequent adaptations a little bit. So does this also explain why people will say that exercise is generally good for your health? Would building antioxidants in your muscles at all have any sort of... Building like a diet perspective or just exercise? Yeah, so I'm sorry, let me rephrase that question. Would these... Antioxidants within the muscle cells always be confined to the muscle cell themselves. Yes, they would. So this is not like you are megadosing vitamin C or something like that. No, actually, you're bringing up a really good thought that we're going to get to in a little bit. I've already got that planned out. So we're going to get there. Yeah, and I actually think this brings up an important point of, you know, if you're not that well trained and you do a lot of exercise, you know, initially you're not going to be able to handle certain things, and that's what adaptations to exercise are all about. And that's what, I mean, that's what, you know, this podcast, among other things, are all about. It's what I do with my spare time when I'm not actually, like, on Training Peaks coaching people. So, alright, so the reason that, This is important to know is that they show that the reanodyne receptor fragmentation is due to reactive oxygen species. And already in the literature at that time, it was known to be susceptible. So this is actually just more replication of previous results, which is always good in science. So the next experiment they did, they took mice and they did, the mice did voluntary running. It's important that they mentioned that and I mentioned it because it was 20 kilometers a day. Yikes. Although, I actually have seen, I saw some other study of like estimating, you know, if you have a pet hamster, a pet gerbil, like how far are they going to run in the middle of the night? Because they're, a lot of times they're nocturnal and people wheel, like you'll just hear them running all night. And some of them actually do run a surprising distance for this little tiny like four inch long creature. Yeah, so they did that 20 kilometers a day for 40 days. And they obviously had a control group. So what they then did was they stimulated the mice muscles in vivo for the same 6x30 second protocol above, right? Okay, so to get mice on a little bike, so this is the next best thing. And then they measured reactive oxygen species generation by a fluorescent marker. And these sedentary mice saw a 200% increase in this fluorescent marker, and the trained mice only saw an 80% increase. Interesting. Yeah. So they, they, so they had already genetically modified these mice such that when they have, when they produce these... No, I think they just, they just added a marker into the cells. I don't think they genetically modified it. I was like, did they modify the mice so that when they produce these, like, antioxidants they, like, spit out? No, well, it's what, it's the... The fluorescent marker actually glows fluorescent when it encounters a free radical. Okay, okay, sorry. I was thinking they'd like GMO mice that express like GFP when they express antioxidants. They like sweat green when they... Oh, yeah. Actually, if anybody hasn't seen it, obviously glowing mice have been engineered. So that's cool to check out. Yes, that's what I was imagining. And that is not in the show notes. So then they then repeated this experiment, but this time they added a general antioxidant to one set of the muscles and not to a control set of the muscles. And what happened was the antioxidants completely blocked reanodyne receptor fragmentation. Interesting. Yeah. How cool is that? So the paper actually suggests that this is due to enzyme cleavage of the protein. Because, you know, like previously mentioned, the immunoblots, you know, because it gets snipped in the same two spots, it seems. So we end up with like a 300 some odd kilodalton fragment, like an 80 kilodalton fragment and like a 40 kilodalton fragment or something like that. And if it were random, we would see a lot of different fragment sizes, right? And because it's not random, it's in a couple spots, that's what makes them think, that's what would make me think it's actually a very specific enzyme causing this. And the authors suggest calpins or calpains, which are three to four times more active in the control group. Then the antioxidant group, but obviously the authors suggest the need for more experimentation to find out that particular mechanism. That's really interesting because you think like, oh, receptor fragmentation and it really is very specific fragmentation. It's not that these things are just breaking or tearing apart or something. It's in some uncontrolled way. It's actually a very controlled mechanism. Yeah, and it's interesting too because Why would our cells have something to precisely snip up this receptor? I don't have an answer for that. Yeah, it's super strange. In a way, though, it kind of reminds me of sort of the way that your body would cause necrotic cell death or something, right? It has a Oh yeah, sure. Prescribed way to go about getting, you know, sort of taking out the trash. Yeah, and mitochondria are very important in that too also. So the question is, why would we have ranodyne receptors specifically as a target for this and why does this happen and not like other structural proteins? Why not SERCA and dystrophins or whatever else there is? I don't know the answer. Hopefully someday somebody finds out because... I'm curious about that. Alright, so the last experiment here, so we're at like what, like five? They did another mouse prep of the same muscle and with the same simulated quote-unquote cycling bouts and they found the same fatigue. Little mice, little bikes. I would love to see that. They found the same fatigue. of, you know, the lower contractile force when electrically stimulated because it's hard to ask a mouse to, you know, contract really hard. Lots of cheese if you push really hard. Yeah, but this time they measured calcium concentrations in the muscles. So the calcium in the cell during the simulated cycling bouts decreased significantly from the first of the 30-second bouts to the sixth. And not only that, but immediately after, there was, at rest compared to before, the HIT protocol, 40% elevated calcium concentration. That got leaky pretty fast. Yeah. Yeah. And this is the kind of signal that in many studies, you know, I didn't pull any, so you can just refer to references 14 through 16 in this paper, which paper's open text again, so check that out if you want. So the paper also discusses something that's probably important. for us to think about, although it may not actually be in any way important for us to think about, but we're going to talk about it. So what is the mechanism of the fatigue, the forced depression and the knee extensions, you know, real or simulated? So in trained individuals, increased antioxidant capacity, right? So the fatigue is there probably due to decreased sensitivity to calcium. because there's no ranodyne receptor fragmentation. So the calcium handling ability is probably a little bit compromised in the untrained individuals who are getting the fragmentation happening and the leak. But in trained individuals, obviously that's not happening. So it's probably the fact that the myofibril is actually getting less sensitive to calcium. So there's a trade-off in the fatigue between the trained and the untrained, it seems. That's how I read the authors of this paper. Yeah, it's interesting. So you actually have two – you may not know this is going on in your body, right? As you go from being sort of relatively untrained to relatively trained. These types of intervals are still going to be really hard, and you're still going to be exhausted after doing them. But the reason that you feel exhausted is actually slowly changing inside your body, which is kind of cool. Yeah, that is really, really cool. And actually, there might be other stuff at play here. We're really only limited at this point to what the authors measured and interpreting their results. You know, a lot of the times I actually disagree with some of the interpretations of some papers, which, you know, and not just the Ronstadt paper, but I mean, yeah, but a couple other papers, a lot of other papers where I've said, you know, this might be a problem, this might be a problem, you know, kind of going down the list. I actually have very few, if any, criticisms of this paper. It's one of the reasons that I've liked it so much for so long. So here's the asterisk. So remember the asterisk that we brought up earlier? So remember this paper started as an attempt to kind of find a minimum dose for HIT given the wide support for HIT efficacy in the literature for increasing aerobic capacity, blah, blah, blah. But they went about it the same way as I think I would have. So maybe that's another reason I like it so much is because I'm of a similar mind to these researchers. So yeah, there could be some confirmation bias here. So now that I'm biased, let's talk about this. Given that reactive oxygen species are more well buffered when trained, meaning there's a little less of that stimulus, or a lot less actually, and there's less if any calcium leak because of no random unreceptive fragmentation, there may not really be any reason to expect trained individuals to aerobically benefit from this kind of training. And that's why HIT training may not make you faster. Interesting. So there is actually a reason maybe that people who are recreationally active and why maybe programs designed for people who are recreationally active really find a lot of good results from doing a lot of HIT or advocating for more high intensity intervals. versus more traditional aerobic training for, quote, like, you know, faster results in less time or something, whatever you want to. But that's because the audiences that they're targeting and maybe the people that these coaches or the people writing these programs and stuff are working with are more toward the recreationally active side than the elite, well-trained side. Yeah, that is a very, very good thought. I mean, that's something I think about all the time. Somebody's like, well, actually, it's pretty well-received coaching wisdom down the generations that the program that gets you, you know, from off the couch to level one is not the same program that's going to get you from level nine to level 10. Right, yeah, otherwise you could just keep doing 2x20 forever and then right away up on 2 for a win. Yeah, and actually, I should go find this paper. I think I have it somewhere. There was a paper that actually was looking at HIT training over time and resulting PGC1-alpha transcription of the mRNA and some, you know, aerobic enzymes like citrate synthase and HAD and all that other stuff. They actually... saw a declining amount of PGC-1 alpha transcriptions and a plateauing amount of aerobically active enzymes and enzyme activity over the course of like seven sessions or seven weeks or seven sessions. I think it was seven sessions. Yeah. So I should go find that because, you know, this is what we're talking about because As you go and you adapt, you get used to buffering the signal because for your fitness it's better and you actually need to start changing your program. But regardless of that, some of the usual mechanisms of an increase in VO2 max, aerobic capacity, wouldn't really be seen in an interval session immediately like six by 30 seconds all out. In other words, For just one session, of course. But it depends on what else the person's doing, right? So we wouldn't expect to see much in the way of stroke volume or hematocrit in response to 6x30 seconds. But we would expect to see some mitochondria made, and that can increase AVO2 difference. And I would also potentially maybe see a little bit of plasma volume depending on training history and stuff like that. So another thing that I would actually expect to see in... These recreationally trained men after one session would be like better regulation of blood perfusion through a muscle and also cooling. So, you know, depending on the environment, you know, sweating a little better, a little earlier and systemic hormonal changes would also help improve fitness and VO2 max early on from like a couple sessions because it can take some time for real aerobic training to set in. I've never given somebody a workout, no matter what it is, and expected the next workout I would have to adjust their FTP or anything like that. That would be amazing. You just do only that workout for the rest of forever. Yeah. Yeah. Yeah. So anyway, so yeah, that's one of the reasons I like to study is that they really get into the mechanism and why these adaptations are happening. They didn't go so much into the, you know, How much VO2 max increased? Because that's one of those things where it's phenomenological. It's not, you know, the nuts and bolts of everything happening, which is what I always think about. You know, most AHIT studies and a lot of studies in general in exercise physiology just don't look this deeply. They do some measurements and they call it a day, which is economical, and I'm not going to fault anybody for that kind of thing. I know what kind of pressures researchers are up against. You know, but for someone like me, it's like saying, we made your car faster because it's now faster. Why? Like, does it rev higher? Is there forced induction? Is it lighter? How are we measuring fast? Is this a drag strip or, you know, is it a road course? This makes me think of this famous clip where an interviewer asks Richard Feynman, a famous physicist, Nobel Prize winner, why two magnets attract when you point the opposite poles together. and he goes on this long tangent of basically saying why questions are actually really hard saying that these two magnets attract well they attract because you put the two opposites together well why do these opposites attract and then you have to go into this deeper and deeper and deeper and digging into why questions can actually be very difficult even though it seems like why should be a relatively straightforward answer well because why always has another layer to it So you can get into Maxwell's equations for that and then you can get, well, why does that happen? So at some point you're really like unraveling the fabric of the universe itself. Kyle, I'm looking at you. Have you been unraveling any universes lately, Kyle? Not yet. Trying. Trying. Yeah. Okay. Well, so, I mean, there's an implication here that I'm sure a lot of people are wondering. Does this mean we should avoid foods with antioxidants? for fear of blunting these adaptations if you're just getting off the couch in particular. The answer is no, of course not. If you're eating a normal and healthy diet, it's fine. My carnivore diet, all meat, all the time. I mean, okay, so in a normal healthy diet, you know, a lot of fruits and vegetables and stuff like that, you don't get enough antioxidants. where they will be in such a concentration in your muscle cells that they're going to really interfere. They can have some benefit elsewhere in the body because there are obviously other free radical problems elsewhere in the body that are not muscle and exertion related. Obviously, I'm not a doctor. I cannot comment any further on that. Just in the literature, I've seen a lot of stuff on that and it certainly is an issue. Keep in mind, like, vitamin C helps you stave off scurvy, so unless you want to be like a pirate from like 500 years ago. Yeah, if you don't want your fingernails to fall out, you're going to eat your oranges. Yeah, you still eat oranges and leafy green vegetables and all that stuff. Also, if you're taking like emergency or other over-the-counter stuff, by the way, that doesn't actually help with colds, this actually made blunt training adaptations. have been shown, I think the doses were like 500 grams and 4 grams of vitamin C and or E. The 4 gram dose blocked adaptations. The 500 milligram dose did not. So I think if I remember correctly, a typical packet of like emergency or airborne or one of these other over-the-counter cold remedies is usually around a 1 gram dose of vitamin C. Yeah, I would say that's borderline. And so, yeah, it seems like the sort of thing. Just don't take it right after a training session. Yeah. It also seems like the sort of thing where, again, me, be me, naive a little bit. If you want to actually absorb all these vitamins, you maybe want to actually spread out the intake throughout the day in your meals and not just... Glug down a huge, you know, gram of vitamin C or something at once. Because then the next time you go to the bathroom, you're going to look in the toilet and you're going to see that, like, you're just peeing out all the excess vitamins. So earlier, we had alluded to something where, you know, it was a cell specificity kind of question. And, you know, this is kind of what we tried to get across in the last episode. It's that there are fiber-specific adaptations. And we also tried to parallel endurance training with repeated sprint training that can make aerobic adaptations in larger motor units due to signals like these. So, you know, in the larger motor units, not very well used or frequently contracted, they may not have a good ability to actually buffer free radicals. Potentially, yeah, and... I mean, because I've never seen a study on this. This is really just me putting puzzle pieces together and make a podcast about it. So if somebody does some experiments on this, I'd love to see them. But there's very, very few people actually doing single fiber experiments and analysis like this. A lot of times it's homogenate. And so we actually have an average over all fibers. But I would also expect to see improved glycogen storage and improved buffering capacity of other things and metabolites, increased Mitochondria and stuff like that. So, I mean, I think the thing that I'm trying to get to here is that the thing about training with muscles is that muscles and cells in general are not actually just trash bags full of parts. It's not like your dad's old toolbox where all the wrenches and screws, everything's all together. And maybe building materials, you know, it's just one big thing. They're individual cells. And in muscles, they're parts of motor units. And they're highly structured. Very, very highly structured. You know, more so than I think, you know, even I, who I've read a lot into the cell structure literature and, you know, probably more than even, you know, the researchers realize at this point. And I look forward to doing a podcast about that someday. But muscle cells are large. They're very large, and they're multinucleate, meaning they have more than one nucleus. And this helps a cell manage such a large area. A big cell like a muscle cell with only one nucleus would be like having one post office for a state the size of Nebraska. Yeah. And incoming mail is like adaptive signals, and outgoing mail is like the mRNA and subsequent adaptations. And if you have to wait a long time, like you can wait forever to get mail in the corner of Nebraska, but if you're right in the center where the post office is, then you're going to get your mail pretty quick. So that's maybe actually a good metaphor for diffusion too. And that's why muscle cells have many nuclei. But some things don't make it between cells. Glycogen is not transferable between cells. And some adaptive signals... are also not transferable between cells. Calcium, like, you know, maybe you can get a little calcium leak into another cell, but not to the degree that, you know, like a 40% increase at rest due to leakage. Yeah, that's a lot. Yeah, you think, I think normally people, at least I kind of think naively, oh, like a muscle. Like, you almost just think, you don't even necessarily think of your whole muscle as being these different motor units. You just think of, oh, I'm like... I've got a mix of these like faster twitch and these slower twitch fibers in there but they're all kind of the same and they all kind of work together and you don't necessarily think about how they're organized like this and the fact that you could have two muscle fibers sitting next to each other that have experience. Yeah, one of them's working and the other's not. The inactive one is actually just getting squeezed or something every time I'm on the track. It's a pleasant massage. Like it's along for the ride. And you can, it's weird to think about that you can be running or sprinting on a bike or going on a long ride and adjacent muscle cells in your legs are actually experiencing different conditions because one of them is not at equilibrium. The other one's just like... sitting along for the ride. Yeah, I mean, and this is something if you refer to Wattstock number nine, see that one I've got committed to memory now, which was our first foray into introducing the size principle. The size principle is always active and it's always conserved. Any, sorry to say, any papers that see seemingly or, you know, the authors may put forward a thought of maybe this actually violates the size principle and in fact the size principle is to the best of anybody's knowledge especially very respected muscle physiologists whose papers I read a lot it's always always always conserved and so the size principle is you know being so highly conserved is actually one of the most important things I ever learned in terms of thinking about training adaptations. It's applicable everywhere. And we've talked about it in probably like half of the episodes that we've done so far. I know. Well, and so, well, to bring it back to this, so here's an advantage of high-intensity training for people who do lots of low-intensity training is that, you know, the adaptations, you would now get these in larger motor units like we talked about last episode. Like calcium flux probably doesn't transfer between cells. I mean, I'm sure some leaks, but it's, you know, it's a two plus charge, so it's probably not going to permeate through the membrane because it's too charged. You know, sodium doesn't, so why would calcium? But presence of oxygen and reactive oxygen species would be an example of a signal that doesn't technically make it between cells, but with the nature of capillaries being shared between cells. and the nature of diffusion itself, you know, let's say we've got perfusion of a capillary next to two, two actively contracting muscle cells and also next to, let's say it's between three cells and one inactive cell of a larger motor unit. So we've got a capillary between three cells, two are contracting, one's not. The inactive cell is probably going to experience some oxygen flux. because of just the nature of oxygen and diffusion. It's not, I mean, it's probably going to go mostly to the places of the low pressure gradients below, but probably some of it's going to diffuse upward into that cell and cause potentially some reactive oxygen species and maybe a little bit of mitochondria building up. So I actually have a pet theory that this is a big reason why just about any type of training changes Type IIx fibers to IIa. which really just means that they have more mitochondria among other a couple other things but yeah increase that oxidative performance yeah slightly yeah pet theory probably nothing to it now we're actually back at our asterisk because the odds are if you're doing normal amounts of training and normal training of you know type I would normally assign people and you're racing a lot too or even a moderate amount. HIT-type stuff will probably not cause that many aerobic adaptations, but they'll be better for building anaerobic capacity. So like last episode, we talked about people who regularly have very large motor unit contractions. They're probably extremely well aerobically trained. So if you're like a former rower or something, this kind of training is probably not going to do that well for you if you do 15-15s for 40 minutes because you're probably already pretty good at it. This kind of thing might be good for like specificity and yada yada, but it's probably not going to lead to the aerobic adaptations we're talking about here due to, you know, reactive oxygen species triggering the cleavage of random receptors and subsequent calcium leak. Also, if you're getting better at something like this, like if you were like, is this, if you know this is the thing that you need to train, just plugging away at something like this, You know, we'll probably see, you know, reduced capacities or reduced adaptive capacity in subsequent sessions. But this is another reason why you might need to do more. This is one of the reasons that, you know, with a lot of training and endurance, we always do extensive work because the signal is never as strong, you know, like that first cup of coffee you have ever. Yeah, no cup of coffee is ever good as ever again. Yeah, exactly. Because, you know, your eyeballs are rattling in your skull after that first cup. And now it's like, you know, I'm not even awake until I've had four shots of espresso. Right. Anyway, so after this episode had been written, actually, a very thoughtful listener sent me a review paper just published. I've got a link to it in the show notes, so thank you for that. The paper actually looks at something a little different. They're looking at how sustainable frequent training of HIT training methods are. But the kind listener also happened to highlight the section that I would have taken away for this episode. So thanks again. Somebody was reading my mind perfectly. It was great. So the section that he highlighted notes that when it comes to the mechanisms of actual performance improvement in HIT studies, the ones that they look at, because they look at a few in that paper because they're looking at entire cycles of HAT training for weeks. The studies that track these things are usually not seeing, according to this paper, are usually not seeing an increase in cardiac output or hemoglobin mass, but they're suggesting that mitochondrial density and motor unit recruitment as primary adaptations. That makes sense. These big all-out efforts, so you think like If, as we talk about, as you fatigue, and we talked about this in, in Wattstock number nine, where to, to call on those larger motor units requires a larger neural drive. Well, in all out 30 second efforts, you're giving it like all the neural drive that you can. And so you're gonna, you're gonna drag in these large motor recruit, large motor units. Yeah. And the neural drive fades if you start with like a max sprint. Yeah. Everyone who's tried a 30-second all-out effort definitely knows that feeling of like the first 10, maybe 12 seconds you're like flying and then it starts to get kind of dark. Yeah, literally the world gets dark. Your vision. Actually, the WatchDoc number 19 is where we talked about starting efforts with like, you know, All Out Sprint for V2 Max purposes, but the EMG is actually in there. So if you want to check out that paper that we referenced, the cover art for, it should be over there. And also every time I mention cover art, some people have asked me recently, you know, how come I don't find the cover art because you're listening to it on like Spotify on your phone, so it just brings up the podcast logo. Head over to the website or the SoundCloud and you will find it. Yeah, so actually then the last section of this paper. I thought was really interesting. And I was like, aha, somebody else was way ahead of you. I was going to say I am, but I'm only reading somebody else who's ahead of them. They wonder at the mechanism for the increased mitochondrial density in this paper, which was published this year, 2020. And we just went over one of the mechanisms. There potentially are more. But, you know, we just went over one of the ones that they looked at. So there could be a lot more to this. And as I find more research, we will bring you more clickbaity titled episodes. We'll get into that. Those are the best. Yeah, I think it's super interesting because you think like, well, why? Why can't we just do the same training over and over and over again? Aside from the fact that, yeah, you adapt and you get used to and sort of comfortable with doing 2x20s, then you got to do 2x25 or 3x15 or something. You got to push yourself a little bit. But why doesn't doing something like this where you think like all out, well, if I keep doing these 30-second all out efforts, like as I get faster, well, all out's going to be harder, right? I'm going to make more watts. I'm going to go faster. So shouldn't that keep on? being a really good stimulus because it's like if you do one rep max squats all the time in the gym, like, well, when you start off, that's only going to be like 135 pounds, but then it's going to be maybe 185 or 225 or something like that. You're like, oh, well, it's getting harder, right? So why am I not getting the same stimulus out of it? And I also, and you mentioned this, right, where you're training. more extensively, so you're actually pushing the time out and adding volume, not just, while yes, you ratchet up the intensity in an absolute sense every time that you do one of these rounds of all-out intervals and you get better, the absolute intensity goes up, but the relative intensity is gonna be the same-ish. Right? Because you get fitter, so you can produce more watts, but that's still only all out for you. Yeah, the proportion of 100% to 100% is one. Yeah, it's always 100%. Yeah. And so you have to challenge your body in other ways. Yeah, well, I mean, submaximally, too, it's interesting because as... You know, there's something to be said here for increasing anaerobic capacity as well. Because this is one of the things where if you're really, really well trained, you've got your, you know, all of your motor units are well trained, everything's got great oxidative capacity, everything's awesome, and you increase your anaerobic capacity, these 30-second all-out efforts are, you know, potentially going to lead to some better stimulus. However, because you've really gotten to the top of the mountain or you're very, very close, there's even when, you know, let's say your 30 second power goes from, you know, let's say 700 watts to 850 watts or something like that. It's awesome. But it's still not going to be the same stimulus. And in fact, because It may be counterintuitive because the absolute stimulus of 850 watts may sound a lot compared to where you were at 700 for 30 seconds, but you have also trained yourself to deal with the consequences of your actions, which are doing 30 seconds all out. And so the 850 watts actually may not be nearly as good a stimulus as 700 watts was initially. Ah, interesting. Yeah. That's interesting. Yeah. So like 100% is still 100%, but it's actually not even as effective as 100% used to be. Yeah, exactly. It's interesting. And I mean, that's what I mentioned with the papers before looking at the HIT training and seeing the PGC-1 alpha expression dropping through sessions. Go down, yeah. Yeah. And the subsequent adaptations of aerobic enzymes, HAD. Not HID, not HID, HAD and citrate synthase, which are in mitochondria, you know, so they can be a marker of mitochondrial density or just, you know, protein expression in the mitochondria, whatever number it is, those plateau. And so that's, you know, that's one of the things where, you know, is that, you know, are those subjects 30 second powers going up? Probably. Is their last 30 seconds going up? Probably. But the signal is actually going down. Yeah. And that's one of the reasons that One of the things you might do is do another interval, if you can. And that's not one of those things that it applies everywhere, because like we talked about in the VA2Max series, the mechanism of improving VA2Max that we're looking at, or that I'm looking at anyway, is increasing diastolic filling pressure and cardiac hypertrophy. That's not something where you can... Well, that's something where 100% is 100%. And so you have to increase the time. Yeah. Yeah. And it's, it's, it's one of those things where like, you know, just because your heart can get to, you know, 200 milliliters or whatever in that, this ventricle, um, and next year it's like 210 milliliters. Um, does that mean that, um, you know, does that mean that if you do, you know, you fill it up to 210, does that mean that there's less stimulus? No, actually it's probably the same stimulus. So in some things in high intensity, it's the same stimulus. doing a five rep max is this at your, let's say you're pretty well trained and you're at, you know, your squats at 225, you do a five rep max, you know, at like, I don't know, whatever it is, like 185 or something, pounds for Americans. And then later on, you're at 300 and you do a five rep max at, you know, 255 or whatever it is. That's the same stimulus. Yeah. Right. Yeah. So the absolute and the relative. It'll change based on what we're looking at for adaptations and all that other kind of fun stuff. Yeah. Well, I think that's super interesting still because that means depending on how you are phasing your training, depending on how you are feeling towards reaching some goal that you set, you want to change strategies depending on the type of training it is. You can't necessarily program, say, anaerobic capacity training or sprint training the same way that you would. Sort of, if you could just copy, paste, and change some zeros around, it doesn't become aerobic training, you know? Yeah, no, you're 100% right. If only, right? If only you could just prescribe one periodization method for every sort of athletic endeavor. Oh, yeah, well, this is why I'm always thinking about what's the underlying thing that we're doing here. You know, just intervals X increase V to max, that's not enough for me. And maybe I'm... just a stickler for this kind of thing, and maybe I'm annoying to some people for that, and I'm sure I am. That's okay. I mean, you know, we're putting this out there. You know, we're not immune from criticism, and I've certainly personally received my fair share, which is fine. I don't necessarily think that just because we put something out means that, you know, I have to be there to defend it every time somebody... No one's infallible. It's not like... Yeah, definitely. No, you know, you put something out into the public sphere. you know appreciate it or not or whatever but for everybody who is listening and who is enjoying what we're doing we really appreciate you so yeah I think this is a good this is a good kind of deep dive again because we talked about this a little bit in the in the original high intensity interval episode so it's kind of nice to come back to some of these things where you can pull this pull on this thread through all of these different series and say oh but now that we We talked about this a little bit, and then we went off and we talked about VO2 max for a little bit, but now we come back to this high intensity intervals and you kind of see how they're different now. Now that you've seen some of the VO2 stuff, you can kind of compare these two. Yeah, and I remember when I originally wrote the original HIT episode, which I think is actually our second most listened to episode, which is pretty cool, I guess. I knew that we were going to do this episode. and I knew that I was going to title it YHC Training may not make you faster. Stop making you faster. Because, you know, I think we alluded to this in that episode a little bit. So this would also just, you know, tell your friends. This is, this is, we don't just go off on random tangents. We do make it back to stuff that we talked about. We eventually make it back to stuff. We do increasingly large concentric circles in the woods until we find our breadcrumbs. Alright, so everybody, I want to thank you all for listening. I ask you to subscribe to the podcast and tell a friend about it. Give us an iTunes rating. We would love a five stars. We have mostly five stars ratings and we really appreciate that on iTunes. Remember that we're also ad-free, so if you'd like to donate, you can do so at empiricalcycling.com slash donate. We have the show notes up at empiricalcycling.com. We've got merch at empiricalcyclingpodcast.threadless.com. If you have any coaching and consultation, inquiries, questions, comments, you can email me at empiricalcycling at gmail.com and at empiricalcycling on Instagram. We have AMAs in the Instagram stories. Last one was really fun. They've all been really fun. So thank you all again for all of those. With that, we will see you next time. Thanks, everyone.