When VO2max turns Anaerobic 💥

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?

Yes much better all round.
Yesterday legs were just too lactic / acidic / etc and were shutting down. Got tonight’s about spot on.

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I’m basically doing a three week block. VO2 hard start sessions 3 x each week, 1-2hr endurance ride, and a 3 hr bunch ride. I’m hoping the VO2 focus for three weeks will help break through a bit of a mental block. I’ve just finished session 6, and it’s going well so far.

Let us know how you get along with 3 VO2 sessions per week.

How long should you be able to hold anaerobic interval though? - I struggle with inside/outside ration - and when i do the subscribed vo2 sessions outside for 4x4m lets say - i rarely look at power meter, and im just going to go as hard as i can - since i know 4x4m vo2 max have me clinching for those last seconds each set. But outside i can do 375w, and inside im more in the 320 ish. Just took an FTP test outside 2x8m - and came out with 2x at 368//364w - was that too anaerobic or vo2 though? Am i failing to get any vo2 session done outside basically ? And should i try to focus more on holding abit back? (alltought i think its hard to just keep at a number wiht uneven roaads.

My FTP inside (took on a ramp test) was at 288 three weeks ago

You cannot doo too hard vo2 max work. Especially with longer sessions like 4min and 8min. If you go as hard as you can you are burning your anaerobic contributions and go into higher percentages of vo2 max - so maximal aerobic. Especially when recoveries between intervals are short.

When you are doing intermittent intervals like 30/15s or 40/20s you recharge your anaerobic contribution and these become a more anaerobic workout. With longer intervals, you go as hard as you can and you always end working aerobically.

Here’s the energy demand contribution for better illustration

Or simplified:


I just go as hard as I can manage. As above you’re not going to get much anaerobic contribution on the longer periods.

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I think I’m in the V02max range when i can no longer decide when to stop breathing in. My body decides. It’s like there is a valve which suddenly clamps shut even when I know I need to get more air in.

I’ve done two weeks, 1 week left. Week 2 was better than week 1 so feel confident I will get through week 3 and earn a rest week.

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High North has a good workout based on this study. 5 x 6 min decreasing power intervals, 3 min between reps. I barely made it through four today, and I missed the power targets on the fourth. 4-90 sec steps @ ~ 120%, 112%, 109%, and 103%. WKO had me at 12:15 at VO2 max intensity in 24 min of work. I probably could have achieved more with a higher cadence.

FWIW I did a three week session, “polarized” either VO2max effort or Z2.

Did 3-2-3 workouts per week and didn’t have issues. Took about 10 days to fully recover and about 6 weeks to reap the full benefits: 3% FTP gain in what felt like overnight.


I’ve done 3 workouts in a row in the first week of the block.
First one was messy (went a bit hard).
Second one was 5 x 3mins indoor with 15s hard start. This was satisfying but painful.
Third one was outdoor on hills of 5 mins. Felt good and mentally much easier.

Overall I’m pleased as I was not sure I’d be able to get the intensity. 90g carbs in each 90 mins session and high carb during the day.

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