The Importance of VO2max Zone Accuracy?

Okay, so first a quick bit of background; every year for the past 2-3 years, I’ve followed the SSB I and II (High Volume) plans and completely nailed them. I’ve rarely failed to complete a workout other than on a bad day, and seen reasonable FTP bumps.

But then, every year, I progress to the Build phase with above-threshold efforts and VO2max work, and the coin flips. I can usually suffer through the first and second intervals, but then I’m trashed and can’t hold the required power at all, and end up bailing on the workout.

Earlier this week, I attempted Huffaker, following suggestions on these forums that it’s a good workout to benchmark what percentage of your VO2max you can repeatedly hold, as I suspect mine is lower than 120%. It was rough and I had to bail on 2 of the 6 intervals even when aiming for 110% during the second block.

Somewhat frustrated, I decided to attack the intervals from a different angle yesterday. I found a consistent 3min fire road climb in my local woods, and replicated Huffaker outdoors. I completed the workout, and my power across the 6 intervals averaged 117% FTP. However, the power output wasn’t quite as consistent as it would have been had I completed the workout indoors on TrainerRoad, with the watts straying into Anaerobic Capacity towards the start of the interval, and occasionally dipping slightly below my VO2 zone where the hill flattened out slightly. The screengrab below shows the 6 efforts, with the purple line indicating my VO2max power zone (105-120%)

So my question is; how important is it to strictly stay in the VO2 zone? By exceeding the zone at the start of each effort, am I changing the nature of the workout, thus negatively affecting the desired training effect?

Everyone’s VO2max zone is different. Mine is approximately 115% of my ftp.

VO2 isn’t just a power zone, it’s a physiological response. It’s not just saying “ride at this power”, it’s about getting you close to your maximum oxygen intake for as long as possible.

So in fact, going over power in the first 30-60 seconds of the interval isn’t necessarily a bad thing, as it can get your HR and breathing quickly up to that vo2 zone. Same with dropping below 105% - if your heart rate isn’t dropping then you’re still working hard.

I’d be interested to know the average and max HR for each interval as a % of maximum - but in general, they look like a good set of outdoor vo2 intervals to me.

Note how Rattlesnake starts you off at 140% before settling down into the traditional vo2 power zones.


The key isn’t so much as nailing 120% everytime as much as it is staying well paced throughout the entire interval. Starting at 130% and finishing at 105% is not good. If you can do a hard start and get your Hr up and the HOLD, awesome. BUT. You’d be better off starting at, say, 112% and holding that throughout the entire interval.

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Your goal isn’t so much the power as it is getting the right response from your HR, i.e., getting it into the VO2 zone for as long as possible.

As @martinheadon said, extra power at the start or “hard start” actually helps get your HR up quicker. Ideally you want to get it as soon as possible and then kind of hover there. If the rests are too long, you’ll drop out and waste time getting back into the zone.

Now if the power is unsustainable (i.e., your legs are trashed), then you might not finish the workout. Bad since you don’t get the time in VO2 that you want since you bailed early. Or you might finish the workout, but you are unable to get your HR up due to fatigue (what i call system failure) :sweat_smile: Again, if you can’t get HR up, then you’re not getting VO2 time.

If you do it right, it feels interesting. Your legs won’t catch fire. Your HR will wiggle but stay high in VO2 territory. Hence, the recommendations for keeping your cadence high and using a repeatable power so that you can finish the workout. If you have to reduce the power, do so. You can do so at the start or you can do so as you fatigue.


Thanks Martin, good to know. At the end of each interval I was panting pretty well so I’d say they’re putting me close to maximum oxygen intake. As you can see from the graph in my original post, my HR seems to get high and stay elevated without dipping too.

As for those HR values for each interval, I think my maximum HR sits somewhere around 180bpm (reasonably low for my age), which results in the following;

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I think you nailed it pretty well, Luke. Those intervals look fairly consistent and definitely had you up into VO2Max territory. If you go out to the fire road again, no doubt you can make them even more consistent.

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This. Almost by definition, if you do 6x3 min intervals (e.g. Kaiser) at your max capability (same average power for each interval), you’ll be riding at VO2 max.

That might be, maybe, 112-115% for you indoors? You can determine by trial and error.

Nice work on the outdoor intervals! 117% average is a good number, and they are pretty consistent. Is your outdoor FTP higher than indoor?

Thanks Dave! My average power for each interval did vary slightly, but they were within +/- 5w of each other.

I’m not sure about indoor vs outdoor FTP - I’ve always tested indoors using the 20min test, and used the derived 95% number indoors and outdoors. For the most part it feels bang on, but as soon as things go upwards of threshold I have a real hard time sustaining the power demands on the indoor trainer. The only thing I can put it down to is that outdoors, I’m able to stand up and rock the bike around which perhaps helps me put the power down, whereas being sat in a static position on the trainer really doesn’t work for me.

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Is VO2max the most misunderstood zone or what?! :man_shrugging::thinking:

(p.s. - P. Gilbert knows VO2! :trophy: )


Sounds like there may be an indoor vs outdoor thing doing on - whether it’s a difference in standing, cooling or just psychological.

Best approach I think is to dial down the intensity of indoor VO2max workouts by a few points. Or now that the weather is getting better (assuming you’re northern hemisphere!), do VO2 max intervals outside.

The fire road you picked for the intervals above seems like a good spot to get some consistent intervals. I have similar long sustained fire road climbs near me that allow me to do good workouts outside without having to worry about traffic or stop signs.

There was a pretty good article on Xert about how the rattlesnake style intervals are better for some people as opposed to the steady effort style. A lot of it depends on their individual fitness level.

Very geeky article:

I think I’m going to tackle as much of this Build block as possible outdoors this season - Summer’s coming, and it seems to be the best way for me to hit the power targets. Plus, surely it has to be better to put the power down on the bike I’ll actually be racing?! I’m putting together a little database of local hills for efforts, so I’ll have somewhere on hand I can rep for most interval durations.

I’m hoping after a few sessions outdoors, I might ‘get used’ to the suffering a bit more and be able to complete indoor intervals if I need to as well… I’ll see how it goes!