Maximizing Aerobic Capacity

Good morning all!

The experts seem to agree (and Sebastien Weber has repeatedly said it, including on FastTalk) that aerobic capacity should always be as high as possible.

No matter what type of endurance athlete you are (sprinter, time trialist, long distance, etc.) and no matter where each of these athlete’s VLaMax will need to be), everyone benefits from maximizing aerobic capacity.

My question is: how do we achieve this “maximization”? Looking for advice from coaches and experts here.

One factor seems to be: getting as high a training volume as possible; that seems generally non contentious. This is where a polarized approach is helpful - getting enough volume without killing ourselves.

Where things are not as clear is: when it comes to the “intensity” part of the equation, what types of intervals are most susceptible to achieve this maximization of aerobic capacity? I suspect that work above threshold might be helpful, but I don’t know for sure. How much above threshold? What sort of duration? I think the “myth” of the so-called “Vo2 max” 5-minute all-out intervals has been debunked, and that something below that intensity is better (for focusing on the right systems without relying so much on anaerobic capacity), but beyond that: what intensity level and duration achieves max stimulation while still allowing repeatability and recovery?

Is this something that should be focused on for a certain period before then specializing (e.g., in sprinting for sprinters or on threshold work for time triallist) and, if so, for how long?

Or can this be coupled with threshold work more or less year-round, without doing it in separate blocks?

I would love to have a clearer picture here.

Really looking forward to this discussion.

I was re-reading this the other day and it suggested that the key factors in improving performance were the number of work bouts and duration , rather than max intensity (as you mentioned), as long as you are working in the ‘severe zone’ eg >FTP & <MAP.

I’m hoping that means that longer periods of repeated slighly sub-max intensity work will do that job and be much more sustainable than the traditional max effort vo2 work???

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Aerobic capacity is the result of:

  • the amount of oxidative fibers
  • the torque that these fibers can produce
  • the amount, size and efficiency of mitochondria
  • the volume of oxygen you can effectively transport to your oxidative fibers
  • the fatigue resistance of your oxidative fibers
  • you can fake a higher capacity for a certain duration by adding glycolytic fibers to the mix (probably max 90 minutes without refueling)

So to develop that capacity:

  • make as much volume as possible as that promotes the mitochondria development
  • use sufficient intensity to utilise your type IIA fibers (100% FTP)
  • train your type IIX (glycolytic) fibers

A practical application:

  • warm-up
  • perform a 5-minute all-out test (type II utilisation)
  • continue as long as possible (extend)
  • repeat every day, but skip the 5-minute test when sore.

To prevent boredom: change the above into intervals, hill repeats, wheelies, whatever. Just don’t stop after fatiguing the type IIX fibers.
“There is always a speed at which things become comfortable again, that is your endurance pace for that day”.

Thanks largely to @kjeldbontenbal , this seems to reinforce a few things.

  1. volume is a key component to maximizing aerobic capacity. By aerobic capacity, I don’t necessarily mean improving VO2Max itself (though great if it can be improved!) but, rather, “power at VO2Max”, or “maximal aerobic power”.

  2. the other element that is stil unclear to me, despite the good general suggestions made above, is which kinds of intervals are most susceptible to achieve the objective sought in working on that MAP?

Is it still appropriate to dedicate a training block (8 weeks) to first get MAP as high as possible, and then do more work in subsequent blocks on threshold power to reduce VLaMax, capitalizing on that higher aerobic power?

I think I have a good hold on what really reduces VLaMax (longer threshold or near threshold intervals at low cadance), but I don’t know what intervals are best to maximize MAP.

Am I better off with shorter intervals at higher power (2-4 minutes way above threshold, 120-130%) or longer intervals and more total work still over threshold, but not as high, percentage-wise (say, 105-110%)?

Also, assuming that these sessions are very hard, and possibly harder than Seiler’s/Trevor’s favored 4x8s or 5x5, I imagine that once a week is probably all I could tolerate. If that’s sufficient, what could be an appropriate 2nd intensity session for the week, that would still be conducive to good aerobic gains, while not over-stressing my nervous/hormonal system, while complementing the 1st session?

Would be curious to get @trevor and @ryan 's point of view on this?

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Would we great to hear from our respected experts.
I can already say that the number of repeats and the length of the duration, are variables you need to figure out for your own body.

Your goal is to stress your Type II(A)'s so that they will become stronger. That can be done through a short and very high intensity load (“sprint”) or longer sub-maximal load. The duration of the load is something to discover. (so x number of 30s all-out, or y number of HR zone 4 efforts).
Give it a go at a level you think you can handle. Two days later you will have your feedback from the legs. In the meantime, just go aerobic.

Great. Now I’m reading Olbrecht again. Some screenshots from his book (kindle version).

As I remember it, his strategy for increasing aerobic capacity was to interpolate hard efforts into endurance work to engage/involve type IIA fibers. I have attached a screen shot of some of the workouts I was trying out when I read (or at least browsed through) his book in early 2021. I have no idea if this is “right”; basically did a small set of 30/30 to start then tried to hit the fibers a longer intervals during the ride.

The progression from short to longer intervals is intended to be spread out over weeks :slight_smile:

@CEBorduas You’re really getting into the art of coaching/training with your question above. There really isn’t one answer to the question. And @kjeldbontenbal really hit on the right note when he said that you have to find what’s right for your body.

So, I can really only give a few general guidelines and then recommend you experiment…

In terms of the length of the intervals, I have seen athletes use everything from 30 seconds to 5 minutes to train power at VO2max. And I’ve seen them all be successful. All of this is complicated by the fact that almost all training has been shown to have an impact on that power (including sprints and threshold work.) So what length is exactly right really depends on what you find your body responds to. Just a few thoughts:

  1. 5x5 minute intervals with five minute rests at VO2max power has been around for a long time. They are effective, but man do they hurt. If you like them and can do them with sufficient quality then they’re a good choice
  2. I’ve seen a lot of athletes use 2x2 minute intervals at powers around or a little above VO2max. This used to be my go-to interval, but I found it hard to do with quality at altitude
  3. I know coaches like Neal Henderson really like 30x30sec intervals to work that particular system.

In terms of the number of sessions per week, that also depends on the individual. If you can get through two sessions in a week without too much fatigue, then I’d recommend it. But, if you find that too much then I would do something a litlte easier and more fun in the second session. What to do depends on the time in the season. I’ve mixed this work with threshold work (i.e. hill repeats,) sprints, and Zwift training races. But it all depended on the goals at the time.

What’s more important to remember is that all of these workouts are tough and produce gains quickly. You only need 5-8 sessions to see the gains.

Hope that helps!



Thanks for the thoughtful response, as ever, @trevor !

To keep things simpler, I guess the other part of the question I’m trying to figure out is whether doing the work “in stages”, as has long been preached, makes sense. In other words, and since you say that the gains come quickly, does it make sense to do a first bloc of VO2 power work for, say, six weeks, and then follow that up with more threshold work?

I’M thinking that working at the higher powers will likely raise VLaMax, which is a recipe for lowering threshold power, is that correct? And would that validate the approach of “raising the ceiling” first, regardless of VLaMax impact, and then do threshold work to raise threshold power under it?

In the end, my focus hasn’t really changed, and I’m looking at what will make me the strongest on the long term. Not necessarily the sharpest for one race in the season.

if you do the higher intensity, and vlamax goes up, threshold likely won’t fall but fatmax may.

If you incorporate one longer session while you do your harder intensity that might be very good for you.

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@CEBorduas I think Steve’s advice is great!

It is always a balancing act, but are various attributes aren’t always that fragile. Most of us can improve VLaMax without too much impact on our threshold power.

I do agree that doing six weeks of VO2 work is all you should do. By then you should have seen most of the gains and going longer can start to get you stale.

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Thanks @trevor and @steveneal .

I guess the only question is leaves is: what am I doing now? The intervals I’ve been doing for the past 3 weeks have been 5x5s at a power that I would characterize as somewhere between threshold and VO2 max power (probably between 105 and 110% - this is a reasonable guesstimate based on feel and experience, as powermeters don’t always agree and I haven’t tested my MLSS/threshold power formally in a few years). The workouts are a “fun” challenge as opposed to a “tough” challenge. I’m not crippled after them and can train easy the next day.

So far, I’ve been doing those once a week and doing one or two strength workouts, with the rest being Zone 2 riding.

Should I leave things “as is” is or, in line with the discussion above, is there a benefit to doing similar workouts at slightly higher power level for a few weeks, before transitioning to another block of longer intervals at this (or a slightly reduced) power?



Intensify or extend once you can handle them

For what it’s worth…I’ve only done these once but they easily generated the most time @ VO2 as modeled by WKO - Bossi Intervals (from High North’s workout library). You could think of this as a progression from your 5 x 5’s as it is five by five minutes with 3 min RBI, but the five minutes on are done as 3x:

  • 30s @ 130% FTP
  • 70s @ 100% FTP

It is killer. Modeled time at VO2 per WKO for the last 365 days for me is below. You can easily spot the day I did this workout.


@CEBorduas, my only suggested change to what you’re currently doing would be to add a second day with the 5x5s each week. Building that aerobic engine takes a lot of time and work to see significant changes. For many athletes, once per week isn’t enough.

In terms of transitioning to longer work at a similar intensity, that does somewhat depend on how long you’ve been doing the 5x5s and if you have any upcoming target events. If you’ve been doing the 5x5s for a while (i.e. months) then your body is probably ready to hit other target energy systems. A couple weeks of doing longer intervals at the same intensity may have some value just to teach your body to sustain the power you’ve developed with the 5x5s, but at some point your body is going to stop adapting to the same or similar work.

And if you have a race coming up, it would probably be helpful to switch to something shorter and harder (i.e. 2x2s or Tabata’s) to bring around your top end.

But all of that is a bit of guesswork since I don’t know how long you’ve been doing the 5x5s and what you have coming up.




I hope all is well!

I guess I’m no longer clear on the intensity at which to do the 5x5s. I’ve typically done them at around 105% of threshold, and found them to be too easy at that intensity. Which is why I’ve more typically done 6x5 instead.

Is it possible that the relative ease with which I can complete this at this intensity indicates that I need more stimulation, in the form of either longer intervals at the same intensity? Or should one compensate for the relatively shorter duration of 5x5s by going at an intensity higher than 105%?


Trevor also looks at a HR cap + 1 bpm. How does your HR compare?

What are you expecting? 5 minutes right at your FTP should be fairly easy to accomplish.

Has your FTP been correctly assessed?

That’s kinda the point. Twenty five minutes at threshold interspersed with 4 minutes of rest feel too easy to provide much of a stimulus.

Which is why I’m looking for the most appropriate adjustment to make from there.

I often hear, “it only takes 4 to 6 weeks to get results”, in reference to VO2 or anaerobic work, but no one ever says what to do afterward :slight_smile:

For someone who simply wants to get faster every year, I don’t think just 6 weeks of VO2 per year will cut it, so what exactly is the plan? In other words, how often should we return to VO2 and/or anaerobic in a given year? Do we cycle through something like the following?

  • 6 weeks of Endurance/Sweet Spot/Threshold
  • 6 weeks of VO2
  • 6 weeks of Anaerobic
  • rinse & repeat

Another way to ask the questions:

  • How many weeks of VO2 per year should we do?
  • How many weeks of anaerobic per year should we do?


/cc @trevor

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