From VO2 Max to Durability: Rethinking the Key Pillars of Endurance Training

I grew up and it was like the key pillars of endurance performance were VO2 Max, anaerobic threshold and exercise economy.

Nothing else. That's it.

And now all of sudden it's like, ⁓ the fourth pillar is now coming in. This is brand new. Like this is just out of the gates, you know, a few years old. And you're, you know, one of your master supervisors, Harrison, think, or a few of them, ⁓ Ed and Dan, they wrote one of the first papers on this, they?

Yeah. And that was only a few years ago, right?

Hello and welcome to the Athletes Compass podcast where we navigate training, fitness and health for everyday athletes. The terms endurance, durability, resiliency and fatigue resistance have been gaining in popularity among endurance athletes. We're going to be digging a little into these terms, discuss what they mean and how everyday endurance athletes can train to improve their fatigue resistance.

To help us today, we've invited Harrison Dudley-Rode who did his master's degree from AUT in New Zealand on the topic and wrote a recent blog post for Athletica on durability. Harrison, welcome to the podcast.

Thanks for having me.

So maybe we should start with a definition for all of us. What is this new pillar of endurance performance that everyone's calling durability? Can you start by giving us ⁓ a simple definition of the term to get everyone on the same page?

So it's durability or sometimes referred to as physiological resilience. This represents an athlete's resilience to changes in their physiological variables and performance over a prolonged period of time. So physiological variables meaning your exercise thresholds, lactate threshold, critical power, VO2 max. So how those

thresholds decline over time.

It's really kind of fascinating, right? Like I didn't really think about that. You know, if I'm kind of backing myself up into, you know, classic exercise physiology and we test an athlete in a lab and we get their, you know, their VO2 max, we get their thresholds and you just sort of think, oh, those are static. That's what it is, right? You've got a VO2 max of 55 and you're...

threshold is 75 % of that. But that's not what's been discovered, I guess, is that that changes, those thresholds change and they...

They decline, right? Like they don't improve. They get worse as we go on. You know, lot of endurance athletes here like Ironman, right? Like, so your threshold at the end of an Ironman is a whole lot less than it was when you refresh and you went into that lab. Is that right, Harrison?

Yeah, that's exactly right. And I guess it makes a lot of intuitive sense. And I guess as athletes, you all sort of know that feeling of the inability to maintain that pace that you initially set out at ⁓ and that sort of durability in practice really. ⁓ The key for researchers at the moment is trying to figure out exactly how can you train durability? How can you?

Is it something that can be improved? And how can we monitor it in real time? Because I that will sort of unlock a lot of the secrets, I guess, on how can you perfectly pace that race. Because if you sort of contextualize it, what this means is that you might start out a race with a critical power of, say, 330 watts.

after three hours of riding, that might have now declined to 300 watts. So if you're now trying to be within that range ⁓ at a threshold that's now declined, you might be pacing your efforts at your threshold. because it's now dropped, you're now performing at a high exercise intensity, which, as you know, becomes an unsustainable effort.

because you're above that limit.

Yeah, I love it I mean, I've got new thoughts or sort of thinking on the fly because I'm very biased. I'm always looking at those like critical power curves or critical pace curves that we've got on Athletica. But what you're telling us here is that, well, actually as you know, the typical hyperbola or the decrease in that classic curve, everyone's got one. If you're on Athletica, go check out your own curve on Athletica.

you

That's kind of natural as we go and that critical power line that we draw across, well, the context, as the duration lengthens, that actually should be kind of almost going down and down and down, right? Your critical power when you start sure isn't the same as two hours later on, right? It's a fraction less. It's kind of cool.

Yeah. And

the thing is, it's not a linear decline. It's very much non-linear. So you might not see much of a decline for a few hours. And then suddenly, boom, it starts to tank.

And that adds an extra piece of complexity to the mix because it's not always the same for everyone. And in fact, it is very different between athletes. People's durability varies massively.

Yeah, well, perfect segue. You segued yourself. Why is that? ⁓

Yes, the short answer is it's kind of unknown within the research.

potentially likely due to, I differences in fiber types. So one athlete might have more type 1 fibers. Creates type 2, gets another athlete. There seems to be different sex differences as well. So females have kind of shown to be more durable, at least in their physiological durability.

I don't know if there's research that's shown that on the performance end, but certainly it seems like their drop in physiological durability in their thresholds seems to be greater.

Go girls.

Ha ha ha.

Yeah.

⁓ What about what are your thoughts of ⁓ metabolic flexibility and durability?

An interesting one because you would sort of assume that, especially as you deplete your carbohydrate stores, if you were able to metabolize a higher amount of fat, that you would be able to maintain that performance, at least from the fresh values. Peak fat oxidation hasn't been able to ⁓ predict someone to have greater durability. ⁓

But certainly, it can't be a bad thing to be able to oxidize more fat as you start to deplete your internal carbohydrate stores ⁓ and therefore be able to maintain ⁓ that performance.

Mm.

Yeah, I'm very, Harrison, I've had this chat offline before. It's, ⁓ I'm very biased towards kind of believing ⁓ intuitively that metabolic flexibility, Marjaana your point, should be related ⁓ to the level of durability. But to, know, Harrison's right. It's like, it's not, you know, there's some hints in some of the data sets, but it's not definitive by any means. I would say actually the female,

⁓ data that you just mentioned, Harrison, ⁓ that also potentially speaks to that too, because ⁓ women are known to be really good fat burners relative to men as well. So there's a lot of things that are sort of pointing there, but this is the coolest thing about this whole topic is like, you know, I grew up and it was like the key pillars of endurance performance were VO2 Max, anaerobic threshold and exercise economy. That's it. Nothing else. That's it.

And now all of sudden it's like, ⁓ the fourth pillar is now coming in. This is brand new. Like this is just out of the gates, you know, a few years old. And you're, you know, one of your master supervisors, Harrison, think, or a few of them, ⁓ Ed and Dan, they wrote one of the first papers on this, they? Yeah. And that was only a few years ago, right?

Wait, it didn't read.

Yeah.

So.

Why wasn't

this considered a core metric until recently? Was it just something that we figured out was missing from the big picture with VO2 max economy and a threshold? I mean, how are they different?

I suppose the initial joiner model that Paul was just mentioning ⁓ was that the three pillars of endurance exercise were your VO2 max, exercise economy or gross efficiency and cycling, as well as your exercise thresholds as a percentage of VO2 max. And those still are good predictors of endurance performance.

I guess when you then start to realize that those measures which were taken as static measures being in a fresh state, that's what they are. But as we started to realize that actually, if your thresholds are changing, this now adds this other piece that you need to appreciate the dynamic change in those endurance metrics, which is durability. And I think as sort of

learn more about that, began to realize that this new concept durability is independent of those initial pillars and can predict performance independently. just because you have a high Viotamax or high threshold, it doesn't mean you're going to be more durable. So I guess that's why it now should be considered.

Hmm.

need to hold that critical power, critical pace. And ⁓ yeah, they're obviously working on interventions that are going to, going to lessen that decline in that threshold. So maybe that's a good question for you, Harrison. Like,

Obviously it's important, especially in the context of a lot of the athletic listeners here. ⁓ How can they potentially, what are the things that they should work on to, I guess, is it increase? Do I say increase or prevent the fall in ⁓ thresholds, I guess, as they go on?

Yeah,

this is sort of the, yeah, the big unknown is actually how do you get more durable? How do you prevent this decline in performance and in your physiology? And so there's, I guess, limited research that really points to, you know, are there specific sessions that you should do to try and help with this?

At least from these initial papers, it seems that a high training volume, consistency in your training are big leavers in this. Having a regular long endurance session, your weekly long ride, your weekly long run, particularly ones that probably include some high intensity efforts around your race pace.

similar, something with progressing in intensity. And then, like we were saying before, using low intensity, like fasted sessions to try and help that fat metabolism is likely another lever that has potential. And then also resistance training has been another thing that has been proposed as likely

Mm.

beneficial component to improving durability. ⁓ The mechanisms by which it does this is, guess, still also relatively unknown, but likely the ability to maintain your form ⁓ and technique. You sort of see as your form starts to break down, the energy demand for a given pace or power output ⁓ increases. So if you're able to maintain your form, you're

you're not going to see that degradation in your technique, which essentially makes the same power output harder for you internally.

When, when does durability actually like play a role? We have an athletic, we have all kinds of athletes, somebody doing 10 Ks, five Ks and running and up to, you know, like multi-day ⁓ cycling events. So Ironman is durability only interesting to look at.

like past certain distance, for example, half Ironman and up, or is it more relative to the fitness level? Do you know what I mean?

Yeah, would say, I mean, yes, the fitness level.

I would say that at least in the research, most of the studies that we've done at AUT, they've been around that two and a half hour mark, ⁓ where you do see significant declines in your lactate threshold. There's been other studies in runners that have ⁓ been as low as 90 minutes, which have shown reductions in critical speed. And so, I think anything beyond that

90 minute mark unless you're very new to exercise ⁓ is likely going to be the point where it potentially becomes important.

being able to monitor where you are is important for things like training monitoring. So coach prescribes you a session in X, two hours in zone two or intervals in zone four, however you want to design a session.

Making sure that you're hitting, being in that right physiological zone is important to achieve the adaptations that's intended from the session. Also helps to quantify training load. So if you have drifted into another zone, your internal load is a lot higher despite what the external load might.

indicate based off your fresh failures. So yes, that's a key point in order to accurately quantify the work that you're doing so that you can use that to plan the next session or the recovery required. So yeah.

Hmm.

What's up?

So

it's a post analysis interest more so than live monitoring. So if Paul now sends me off to the same climb next weekend, we can see if there's, or let's say in two months when I'm in better form, he could then analyze the first climb versus the second climb and see if my durability has improved.

Potentially. Yeah. And I guess there's a lot, there are a lot more factors that would come into play there. You know, I guess the research from my master's is looking at the effect of carbohydrates on durability. So we know that your carbohydrate availability will impact your durability.

I guess there isn't research yet, but likely ⁓ altitude plays a factor in there. So if you're going above 2,000 meters, there's likely going to be an effect there as well. ⁓ And then certainly heat stress could play a factor as well. So guess there's a lot of moving parts. ⁓ And so making sure those environmental conditions are similar, I would say, is important in order to make.

comparisons between sessions.

Haha.

Yeah, this is a kind of, ⁓ I loved your explanation there, Harrison, on the breathing frequency stuff and its relationship to, it gets telling us something as a workout goes on, right? So as you're out there, Marjaana, out there doing that session on that hill, it might be changing ⁓ under various different contexts. And like Harrison said, it all comes back to the graph.

And it's like the breath is like a signal for what Stevens in Stevens model. It's like, it's like load stress strain. think I get this wrong sometimes, but I think it's like the strain is like, it's kind of like a mechanical engineering ⁓ model, but it's like the, the, the metal is, is, is, ⁓ there's a lot of strain on the metal, right? So the stress can be kind of the same.

Mm-hmm.

but the strain might be sort of different. So your body is like, it might be under different strains, I guess, for different stresses, different loads, something like that. We'll get Stephen to explain it to us next time. But regardless, things change as you go out there. And the breath, how much you're hyperventilating or not, or calm, that's telling us something about how...

it's stressed or strained, are. hope someone can teach it to me, but it's like, it's like how, yeah, how much are things changing? I had this, um, experience with after right after the Steve and Isidler podcast, I a little training science podcast where I went up the hill and eating something before it, my gut was off and it was like, I could really feel my breathing frequency was a lot higher compared to when I usually like, it's, it's a ride to do all the time. And it's like,

It was something was definitely off and I was hyperventilating accordingly. that breath was picking up and it was picking up some other stress that was in my mind. So, yeah, I think it's more of an interesting thing here that we're gonna, but I think we're gonna see this evolve as we go on because I think the time our guys are, is it Visma or whatever they're working with is one of the big teams. Yeah.

Yeah, VIsma

So they're in, yeah, like some of the tour teams are investing heavily in figuring this out. They're at the cutting edge, but we'll eventually see this sort of drift into us, you know, weekend warriors for sure.

Harrison, talked, you mentioned five, at least things that I counted, ⁓ ways that we might improve durability, high training volume, training consistency, a weekly long run or ride, ⁓ resistance training, but then you also mentioned fasted sessions might help with this, fasted workouts. Are there other modalities that might improve durability and can you talk a little bit more about how fasted

workouts might affect durability.

I guess.

So with my research that looked into the effect of carbohydrates on durability of your lactate threshold, did ⁓ a crossover group to one group did two and a half hours of writing at 90 % of their lactate threshold for two and a half hours and then repeated that session also doing. ⁓

you

The same was 60 grams of carbohydrates now. And what you saw was that the carbohydrate group ⁓ significantly mitigated the decline in power output at the lactate threshold. So on average, this was about 3 % decline in the carbohydrate group and about 6 % in the non-carbohydrate group.

Thank

And so this is obviously.

playing a role ⁓ in how you're declining over time. Whether that is a stimulus to improve durability, I guess, remains to be seen. But plausibly, is a greater stress on the body. And potentially, that is in itself a stimulus ⁓ to improve that decline over time. ⁓ And so I guess, yeah.

Mm.

I don't really have a clear answer to it, but in my mind that is likely something going on there. ⁓

Mm-hmm.

So is it better to do intervals at the start of a workout or at the end of a workout to build durability?

That's a question.

It's a good question. Certainly, intervals as opposed to not intervals will increase the rate of decline in durability. you know, certainly the intensity of exercise rather than

the work itself is a bit more telling in terms of what's going to be a stressor on the body and impact that durability. So I'd say as long as those intervals are interspersed throughout, you're still going to be getting that stimulus.

Hmm.

Good question, not too sure.

I don't know.

I'm not too sure either. But you know, we're getting a pretty cool tool. And this is just a perfect, perfect segue to talk about the new newest athletic innovation. We're still working out the kinks of it. But it's it's ⁓ probably going to be called intervals IQ. And it's basically a ⁓ it's it's the work of

Dr. Stefano Andreoli. And ⁓ he's basically invented this new ⁓ feature that basically uses AI to detect your intervals as you go along in any given athletic workout. It's only for cycling, but it's just launched and I'm just so enjoying kind of going through all my different intervals on there.

And, know, we're still working out the kinks of it, but it's really, really cool. And just to not have to actually zoom across and figure out your own sort of intervals, they're sitting there and they're sitting there at the end of your workout. So if you're on to Athletica, make sure you check that out. And yeah, it's pretty, pretty fun.

Harrison, what questions do we still need to answer in the research about durability and fatigue resistance?

A lot. ⁓ As you probably gathered from my vague answers on a few of the questions, particularly around the, you know, how, how are we able to train durability differently? There's more research.

needed on that. think we've almost got the tools to start being able to monitor durability, that is closed. And then more towards what impact does different environmental conditions have on durability. So there haven't been any specific published papers looking into the effect of heat stress or

of hypoxic environments, and then probably more female and age specific research. there has been studies to show that under 19 cyclists are less durable than world tour, pro tour cyclists, but then how that interacts with weather.

cyclists that progress through into the professional ranks are the ones that already have greater durability or if it is a training effect somewhere amongst those groups and how is that actually being trained is probably the key to the next step in the durability research.

Mm-hmm. And adding time ware as well in there too is going to be fascinating when we do that.

Yeah, I'm really keen to get myself one and start messing around with it.

Harrison, thanks for joining us today.

Thank you very much.

Thank you for listening today to the Athletes Compass podcast. Take a moment now, subscribe, share, and let's keep navigating this endurance adventure together. Improve your training with the science-based training platform, Athletica, and join the conversation at the Athletica Forum. For Harrison Dudley-Rode Marjaana Rakai and Dr. Paul Laursen I'm Paul Warloski and this has been the Athletes Compass podcast. Thank you for listening.