How Are VO2 Max Sessions Supposed to Feel?

Sorry if this has already been answered. I did a search and got buried under the mountain of results containing “Vo2 Max,” I perused a few threads and didn’t find the answer to my question, which is:

How are Vo2 max sessions supposed to feel?

I ask because I did Bluebell (30sec @120%) today, and I felt it in my legs a bit, but my heart and lungs were just chillin like tempo. When I did Kaiser last month (3min @ 120%), I was nearly gasping by minute three. In other words, it sure seemed like I was at Vo2 max.

Before you say “Bump the intensity up on Bluebell,” lemme say that doing so would toast my legs more than my lungs, whereas Kaiser seemed to really tax my cardio without overtaxing my legs, which would seem to be the point of Vo2 max sessions.


30 seconds at 120% should be very comfortable and it’s so short your heart rate doesn’t go up that much. I struggle with anything over 2 minutes @120% especially on multiple intervals.

For real?! I must be misunderstanding something.

To clarify, Bluebell and Kaiser both taxed my legs a bit–not easy, but not murderous, either.

But on Bluebell, I’d glance at the screen near the end of the interval to see @chad saying something about breathing or getting rid of Co2 and realize I wasn’t breathing hard at all, and I’d think to myself that I was doing something wrong.

What’s the dealio?

Here’s what Frank Overton of Fascat Coaching has to say. He coaches Phil Gaimon:


My bad, answered the incorrect interval length.

Bluebell is 3 sets of 6x1-minute intervals at 120% FTP

Were you doing it right?

At the end of each set you might feel the way you do at the end of one 3min 120% interval.

With the shorter work/rest intervals it’ll take longer to move your physiology into deep VO2 territory the way the longer 3-5min intervals do. You might just be able to handle the short stuff much better than the long stuff.

Another point to address is cadence. Did you do both workouts at the same cadence, e.g. cardio vs muscular?

In the end, as you said, VO2 work is supposed to leave you almost, if not gasping. It should feel close to the most maximum effort you can do without it being a full out sprint effort.


Cripes. My bad.:roll_eyes:

I was doing the intervals right. I was typing wrong. Yes, Bluebell was 1-minute intervals.

Yes indeed. 95-105, depending. Actually, despite the recommendations being for a higher cadence, I erred lower (95) on Kaiser because I was short on breath, while I could err higher on Bluebell.

Okay. That’s what I was thinking. Three minutes left me short of breath on Kaiser, but even the full sets on Bluebell didn’t come close to that.

So do I toast my legs by upping the watts or select a different workout with longer efforts that’ll toast my lungs?

Good to know. Thanks. :+1:

Looking at the graph on that page, I see biiiig differences in HR between work and recovery periods. On today’s Bluebell, my HR did cute little fast lumps through intervals.

So I’m gathering from everyone’s answers that breathing and HR should be pretty darn high for good Vo2 intervals.

Most definitely. Towards the end of longer intervals often times I’ve got that thick drool/spit hanging down past the top tube. Breathing is extremely labored. And my last 3 minute VO2 workout I was ending at 95% MHR. To be fair I don’t even know what my MHR currently is but, this was from the highest I’ve ever seen which was maybe 6-7 years ago.

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I did Bluebell today. The 1 min intervals were uncomfortable, but doable. I was breathing hard at the end of each interval. I was ready for the 5 min rest at the end of each set. HR was above tempo, but not as high as I thought it would go. My biggest problem today was concentration. Mentally doing 6 intervals in each set was tough (and I usually like short, intense work).

Kaiser has an IF of 0.92, Bluebell 0.87.

That 0.05 difference is quite significant, and can make the difference between manageable and brutal.


I hadn’t noticed the IF. Thanks for pointing that out.

I have similar questions and wonder if I’m training correctly.
Overall I have a low max heart rate, maxing at around 160bpm.
(I’m 49, male, I had an ecg to confirm my heart is ok)

I’ve completed sweet spot base 2 a few weeks ago and started Olympic cross county. Below is my Bear -2 workout. I completed this VO2 work without problems, maxing my HR around 150. My cadence was around 90-95 with a few drops toward 88 (which seems to be my “ride forever” cadence). Ride analysis shoes I spent 22.9% of the ride in the “Aerobic” zone above VO2 and almost no time in VO2. (So I was working hard, too hard?)

So, overall I hit my power targets at 90c, with my heart rate at about 90%. Is this correct? If I raise my ftp or increase workout intensity, or increase my cadence during sets I can raise my HR. 90 minute sweet spot and threshold workoits definitely make me work harder to stay on target.

My philosophy is to compete every workout and not quit.
(I don’t think i’ve ever NOT competed a workout).

I’m happy with my training. It is working and I’m getting stronger and faster.
Am I meeting the intended training goal or should I be pushing harder?
(I realize this is just one workout example)


Just to be clear on a couple points: did you mean to write “anaerobic” when you wrote “aerobic”? If you meant to write anaerobic that makes sense.

And second, “90c” is 90 seconds? If so there is some good research out there (not new or anything) that suggests elevating HR to 90%-ish or Max HR and then time at 90% MHR seems to correlate well with increasing performance at VO2max. Whether that’s power, speed, etc…the gist is athletes get the most bang for the buck with time at 90% MHR. 90% is not necessarily THE HR to get to. For some it may be 96.3% for others maybe 87.4% etc…

Yes, anaerobic (damn autocorrect).
90c = 90rpm.



Ah ok RPM. I honestly don’t know but, IMO I don’t think the RPM matters as long as you are on power and HR is trending higher so that you spend more and more time around 90% MHR.

I fully understand a higher RPM relative to you taxes more your CV system while a lower RPM taxes more the MS system.

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As posted by @bbarrera in a relevant thread:

As per the description: VO2max – “…may not be achieved due to slowness of hear rate response…”; Anaerobic – “Heart generally not a useful guide…” It may just be that your heart requires longer intervals to respond and reach >90% HR.

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Handy table there.

And the HR wasn’t a big concern of mine. Like the table said, “Conversation not possible…” And the 1-minute efforts in Bluebell, even after six intervals, weren’t getting me breathing.

This is the key. Actually I think IF gets ignored quite a lot.

The “work” portion of Kaiser is equivalent to 33 minutes at about 102% FTP.

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It depends on what you are trying to accomplish: move the point of interest on your power duration curve up (higher power at a fixed time interval = power intensity) OR move your PDC to the right (able to sustain a power level longer = muscular endurance). Both will improve your FTP. But what really matters is your target events and what the specific demands are. Of course, we all want to improve our entire PDC curve, so ultimately we need to do both.

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