VO2 MAX vs FTP training

I was listening to another podcast where they were always talking about training at a % of their VO2 MAX instead of FTP %. I was wondering if you were, for example, training at 90% of VO2, what would that be as a percentage of FTP? Is there like a sliding scale or something?

Also, they seem to put a high value on VO2 Max work for triathlon training. I haven’t listened to their entire library but it seems to be more important to them than sustained power? They also mention Zone 2 work a lot so, I’m wondering if they are more like polarized training?

Relationship between FTP and VO2 Max is highly individual, depending on so many factors. Moreover, assessing FTP (even allowing for different definitions) can be done fairly easily - unless you have access to a metabolic cart, VO2 Max cannot.


I’m not even sure that training at a % of VO2 Max makes sense. VO2 Max isn’t a power number, it’s a state of maximal oxygen uptake. The VO2 Max zone is a power range that enables you to get into and stay in that state for long enough to reap training benefits. Theoretically you could ride at 102% FTP and achieve VO2 Max, it might just take so long your muscular endurance gives out first. Or you could ride at 150% FTP and achieve a state of VO2 Max very quickly but you couldn’t stay there for long before blowing up.

Re VO2 work for triathlon training I fully agree. VO2 sessions are great for lifting FTP, and that’s what triathletes (and the rest of us!) need. There is a tendency among some triathletes to do little or no training above threshold, because they don’t race above threshold. I also think a polarised approach makes quite a lot of sense as a triathlete if you’re balancing a lot of volume across the 3 sports.


First, read this paper from 1988.
Determinants of endurance in well-trained cyclists .pdf (2.2 MB)

Then think about the historical context here. It used to be thought (I guess) that endurance characteristics were mostly the same for everyone, or that the work/power/endurance relationship was linear along with VO2. In 1965 the CP model was published, and people started looking at where that was relative to VO2max. But it didn’t really take hold everywhere. So many studies even today will have people train at 60%, 70%, 80% of vo2max which is right in the area where FTP happens. So you get weird results sometimes or often.

Exercise phys and strength & conditioning as a whole are finally getting around to seeing that LT/FTP/MLSS/CP/etc varies, and it’s scaring people about what it means for the validity of the conclusions from the huge body of exercise protocols and literature. But it’s like, big news in some realms, which really shows how cloistered a lot of scientific communities are.

As for the emphasis on VO2max in a lot of lit, it’s important but it’s not. I forget who said it but it was something like a high vo2max is necessary but not sufficient for elite endurance performance.


Just found this blog post which pretty much answers my questions :stuck_out_tongue_closed_eyes:https://blog.trainerroad.com/cycling-power-zones-training-zones-explained/

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I didn’t come here to disparage anyone, but wow, this is a really bad article in terms of the author’s understanding of physiology. There’s no such thing as IIb fibers in humans, there’s no way to tell if you’re using IIa fibers or not at tempo because it depends on the distribution of motor units, etc etc.

well, to be fair, vo2max is pretty accurate in WKO4 or 5 these days.
Can also get it from INSCYD.
I’ve never used the lab setting, but heard that if you don’t have the same tester, the tests can be unreliable.
But yeah totally agree, FTP makes more sense for zones at threshold or below, then things really get interesting and should use WKO I-Levels!


I am no doctor or physio but a quick google shows plenty of published material discussing “Type IIB Fibers” :man_shrugging:

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They exist in other species but not us. We’ve known since 1994, thanks to sds page experiments, that what was thought to be IIb was actually IIx when human muscle fiber homogenate was compared to rat. Smerdu, american journal of physiology I think. Besides that, the article talks about certain fiber types exclusively doing some types of work. This violates the size principle, but also has training implications. :frowning:

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IIb fibers, or IIb myosin?

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Actually, there is an interesting discussion over on the intervals.icu forum about estimating MAP. Also, the latest podcast from Scientific Triathlon has Seb Weber discussing the new protocols that INSCYD uses for non-lab based VO2 max, FTP and other such parameters.


Thanks - That episode has been downloaded for a while, but not had the chance to listen yet. Will do so today.

It’s a new one – up this week.

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Yep, that’s the one. Time goes slowly when you’re homeschooling 2 kids and working a FT job… :ok_hand:

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This is the correct answer. Researchers discovered that humans have type IIx MHC (myosin heavy chain), rather than than the previously thought type IIb MHC. But the the muscle fiber is still classified as type IIb. So type IIb muscle fibers are made up of predominantly type IIx MHC. It’s semantics really, as the fiber type IIb still does what we thought it does, the biological makeup is just different than previously thought. It’s just a naming system. He’s just being a contrarian.

Here’s the research paper he was quoting: https://journals.physiology.org/doi/pdf/10.1152/ajpcell.1994.267.6.C1723

No it doesn’t. Did you even read it?
"relying almost entirely on type I (slow twitch) "
“riding at this intensity begins to recruit some Type IIa muscle fibers.”
“activates more Type IIa muscle fibers than lower intensities”
“relies primarily on type IIa muscle fibers”
“type IIb fibers doing most of the work”

Literally never once states the fiber types are exclusive. It describes which fiber type is predominant, which is correct. It’s a spectrum, and the proportion of fiber type activation will change with exercise type, which is what the article says. Stop trying to be contrarian.


You’re right, that’s my bad. I was remembering the phrase “exclusively anaerobic metabolism” which is wrong too.

Still, “relies primarily on type IIa muscle fibers” is egregiously incorrect. But still all of those statements of fiber type by definition of size principle and mixed MHC expression means they cannot be universally true for everyone. I’m trying to correct what are important distinctions on a very misunderstood subject.

So yes that’s my mistake, so let’s strike “exclusively”, but even “most” or “primarily” or as you say “which fiber type predominant” shows a lack of understanding that impacts training methodologies. It all depends on the velocity and force requirements as well as the individual’s reaction norm to the training environment, which muscle, and where on the muscle we’re looking.

Just sticking with the article’s histochemical categorization, if we look at a spot and you’re using IIa fibers, you’re also using all your type I fibers. If you have 80% type I fibers, odds are no, you’re not using IIa fibers at tempo. If you’re 50% IIa fibers at threshold and you’re only using 75% of muscle mass, that’s still only 25% IIa fibers being used, or 1/3 of active muscle mass. So “relies primarily on type IIa muscle fibers” would require both a very very high % of IIa fibers, but also a large amount of muscle mass recruitment.

Besides that IIx fibers exist in only small quantities in humans. The huge majority of studies on endurance or strength trained individuals will show 0-3%, which makes it exceedingly unlikely they’re ever recruited. After onset of most training programs, most fibers that would be classified as IIx shift to IIa.

Muscle fiber classification is no longer “semantics” at this point because of how much misinformation is out there, or people relying on classification schemes from 1994 and not 2020. It’s been 26 years, we know better now. Histochemical “IIb fibers” are classified as “IIx” in the modern era if we’re to keep from confusion between species, which we very much want to do. If we run sds-page of MHC of rat muscle homogenate next to human muscle homogenate, we see three bands for humans and four for rats. The shortest migration band for humans matches the second shortest migration of rats’ IIx MHC. Rats will have a fourth, even shorter migration in a band corresponding to their IIb MHC. Now if we start plucking individual fibers we will find a range of MHC expression per fiber, but how much of that is hybrid I/IIa or IIa/IIx, or if training shifts fibers to a more focused MHC type over another is very much still up for debate. But still no IIb anywhere to be found in humans.

Somehow, I don’t think trying to educate people is contrarian, but I am hasty and tactless sometimes and I apologize for that. I hope this clarifies things.


WOW! This thread went waaaay above my head, but thanks for the interest! LOL!

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Love the nuance here. Can I ask a basic question since we’re on the topic?

Do human muscle fibers exist along a spectrum of “slower” to “faster”, or is there more of like a bimodal fiber distribution that we call I and IIa/IIx?

Any fundamental references I should read up on? Thanks!

The fibers do indeed exist on a spectrum. There can be lots of fibers that are only I, IIa, or IIx. Intermediate or “hybrid” fibers exist, but it’s very much up for debate how many fibers are hybrids and where they generally shift with training. This is of course MHC. When you do histochemical staining, you’re staining for the ATPase domain, and it’s hard to get a sense of nuance there. For references, check out anything by Jimmy Bagley, but I’d be remiss to suggest anything on muscle physiology without mentioning Walter Herzog.


If you want to get in to 2020, nobody runs SDS-PAGE any more :wink: