When VO2max turns Anaerobic 💥

@TomasIvarsson has a great reply below. While this is a bit harder than needed, you will make vo2 adaptations from it, just with much higher fatigue. This is a lot of the premise from Dr. tabata and Tabata intervals…zone 6 On/off but for vo2 improvement.

Basically ensures your HR gets high and stays high.

google vo2max slow component and you’ll find some interesting info on going easier and longer…I’m becoming a big fan of that.

good luck!


Does not stroke volume peak at around 60-70% of max HR then sit on a plateau up to maximal HR from there?

Yes that is correct, have a look at slide 8 of 19, it supports you claim. Max volume per stroke does max out @40-60% of VO2max, This is why you can improve VO2max with loads of Z2.

Max volume per time unit, however, peaks later. Picture is from this article. At some point the maximal output is reached and pushing yourself further only adds fatigue.

Not always:



Absolutely, I don’t disagree at all. We are all “special snowflakes”! In every aspect it is important to be responsive in your training and see what works for you.


Strictly speaking, the use of the term “anaerobic” to describe a zone of training was a bad choice in the first place… but I’m fairly confident that if I went back and looked at my VO2max block, I spent a significant amount of above 120% of FTP… I just don’t really look at power at that high of a level in terms of a % of FTP as the older models do.

The reality is, for the last interval set that I did, I did 6x3:30 on 4-5 min rest, “full gas” hard start intervals spinning at 110+rpm. If I trust my performance insights for those intervals, on average about 20% of the effort was driven by anaerobic systems, and the other 80 largely by aerobic energy systems. Obviously, that’s sloppy - the earlier intervals would’ve drawn more on glycogen while the later intervals were primarily aerobic… as glycogen stores depleted, aerobic energy system would try to compensate, but power would decline later in the workout.

In short, the point is to get through the anaerobic contribution in the first place and maximize your aerobic power output… then repeat it. So yes, you’ll spend some time in that higher power zone, but as you fatigue and deplete glycogen, you’ll settle into a more aerobic effort at or near your capacity for aerobic work.

I don’t see any issue with those intervals - they look a lot like mine from my VO2max block, and well… that block reaped tremendous rewards for me.

Agreed. I just go as hard as I can for the required length holding back just enough to allow for a quality final interval. If it’s deemed “anaerobic” by a power definition, so be it.

I just wrapped up a block of VO2 work in prep for my first race in a long time this coming Saturday. I’m feeling as strong as ever and I cannot wait to hold the throttle open. This VO2 block had me doing more TiZ than any previous VO2 block and I 100% attribute that to two VO2 blocks late in the 2020 season. I know that the VO2 max system (forgive the crudeness of that) can decline at a faster rate than say threshold, but there’s no doubt in my mind that the blocks that were done last year still had some residuals coming into 2021.


I’ve just completed (tried) my first session of the vo2 block. I find that if I go hard start my first interval just blows me up. I’d need a huge rest between efforts. I started with 5 mins on / off and then reverted to 3z
Also - my HR on an afternoon always seems lower than morning session. I’m struggling to get time above my 90% max.
Any thoughts?

Don’t go hard start. Just do steady-state intervals instead. Hard-start isn’t some magical amazing thing. Also, jumping right into 5-minute intervals is a bad idea. We don’t need to go balls to the wall on the first workout.

I would start with something conservative. Try a 4x3, 5x2 or 6x2 minute workout, and then progress from there.

Heart rate is one of several markers that can idicate where you’re at in relation to VO2max. I would pay more attention to your respiratory or breathing rate. If you’re breathing hard you’re probably close to VO2.


Great advice.
So easy to make irrational training choices when it’s your own training.
I’ll be reigning it in on the next one :+1:

Keep the hard start, but maybe not as hard as you think. For me, I found my hard start at ~400-450W and settled in around 325-340W or so for my max efforts. It’s not meant to be a total blow out hard start, and the intensity of the intervals is not “all out”. It’s “all out” that you can repeat. If your first interval averages 340W and your fourth is down at your FTP, you’re going too hard. Find what’s repeatable “all out”.


How long are we talking for hard start?

I did 15s for anything from 6min down to 3:30 intervals.

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I did 60s.
That’s maybe my issue.

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Yeah, that’s too long. You’re just looking to jump start the HR and oxygen uptake - that’s the theory. 15s hard start, then settle in. I started with 4x5min intervals and as I progressed got to 6x3:30 with longer recovery, over 8 workouts in three weeks. Counter intuitive but it worked.


I was almost going to start a separate thread about this. What do people use to assess the quality of their VO2max sessions? I think what I use is fairly standard: 1 - HR, 2 - breathing rate, 3 - RPE.

I’ve looked at some of my recent and past sessions and think HR can tell me which types of VO2max workouts don’t work for me, but not much more than that. I mentioned in another thread my MHR is 186 but I have no problem hanging out in the upper 170s during threshold / over-under sessions, so from a pure HR perspective I spend more time above 95% MHR in threshold sessions than VO2max sessions. I see more of a difference between breathing rate and RPE between threshold / suprathreshold / VO2max power targets than HR. Could be that I am a total outlier on that.

I posted some notes in this other topic on vo2max struggles:

After a block of two sessions per week crushed me, I’ve had good luck of late by dialing it back and starting really slow - 1 vo2 interval, 3-4 days of endurance, 1 vo2 interval, 3-4 days of endurance, 2 Vo2 intervals, etc.

I’m nailing the hard start intervals with practice and now I’m pretty comfortable pushing 120-125% for 5 minutes. I’m ready for a bigger block next.

I’m probably going to try 40/20s just to see how they go.

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Breathing (during) and dFRC (post ride analytic).


Session 2 done
5 x 3 mins with 15s fast start. All within 10w av, HR and breathing high. Happy days. Well as happy as one can be doing these :+1:


Nice! Did that feel better on the legs?