Why is adjusting intensity recommended for VO2max but not Anaerobic?

Many/most VO2max workout instructions from Coach @chad include something like this:

Important: Try to settle on a demanding but repeatable power output such that you can finish as many intervals as possible. The goal is to accumulate a productive level of stress at a high level of intensity while avoiding the need to frequently quit intervals early.

And that’s oft repeated on the podcast too. My understanding has long been that if you need to adjust down a few %, from say 120% for a 3-minute interval, in order to repeatedly complete the intervals on target then you should. As long as you’re above 110% FTP and/or reaching the desired HR and breathing levels for VO2 work, then that’s what matters most - not the exact % of FTP. For example, I’m having a great day and working really, really hard every single interval if I can complete a 3-minute VO2 workout at 115-118%.

Why are there not similar instructions for shorter, higher power anaerobic workouts like Merced with 40-second intervals at 135%? If I have to down-adjust intensity to complete Merced on target am I missing intended benefits? Or is this the realm where it’s better to skip an interval here and there to enable hitting the target in others?

Every interval above FTP is subject to adjusting based on your personal power profile. That said, 135% with very short recovery for about 5 minutes is going to have a lot of overlap with regular VO2max work.

Power at VO2max is a range of intensities that can elicit VO2max, and is duration dependent. If power is too high, you may run out of anaerobic capacity before hitting your physiological VO2max. The initial 10-ish seconds is highly efficient from a muscular point of view, at recharging your muscles, and is short enough that your O2 consumption shouldn’t drop much if at all. This workout looks like it’s pretty much relying on that mechanism.

In this workout, I would not skip an interval, or lengthen the rest between intervals, or you will fundamentally change the workout. I would take extra rest between sets, or simply lower power a few percent if needed. If you’re hitting the end of a set just barely finishing, and are still able to complete the other sets, you’re doing okay. If that’s not the case, rest longer and/or dial intensity back a notch.


Anaerobic workouts are developing your power output, they require a specific power target.

VO2max workouts are developing your physiological process, which, as already stated, can be stimulated at varying degrees of power output. ‘120%’ is a generalised target.

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In the TrainerRoad world, workouts are classified by Coggan power levels. This leads to confusion about the intent of the workout, which is usually stated in the goals.

In other words, consider two TR workouts targeting max oxygen uptake (vo2max). One uses 120% target power, the other 130%. One will be classified as vo2max and the other as anaerobic.

I could/should add that I’m 50, and while no slouch for my age at 3.9 W/Kg and several years of TR training, I do find the higher power stuff a struggle. Doesn’t keep me from trying though :slight_smile:

Age and W/kg aren’t good predictors of ability to do work at higher power levels. :smiley:

The instructions for Merced mention finding repeatable power (below). I haven’t done Merced but Coach often has tips on modulating power in the workout text. Probably this does too?

“The primary goal is to Improve maximum aerobic capacity (power that relies on high levels of oxygen uptake) by pinpointing repeatable 40-second power and fully stressing your aerobic capabilities in order to improve them.”

As @bbarrera mentioned, Merced is a 40/20 short/short that hits power over 120% so gets tagged as anaerobic, but it says VO2 is the target:

“This workout affords an opportunity to accumulate a lot of time at peak aerobic output in order to improve power at VO2max and perhaps even VO2max itself.”

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@bbarrera, @roflsocks, @jgthomas59 thanks for chiming in. As it turns out, when I tried Merced +1 I failed pretty spectacularly!

It could have just been a bad day (or I psyched myself out by starting this very thread in the hours leading up to the workout :wink: ). OTOH, I did fuel well before and was pretty well rested with this being week 1 of Rolling Road Race MV after a recovery week last week. I did increase FTP with Ramp two days earlier, but that was only a tiny 3W or 1%.

I went in thinking I’d start out trying 100% and down-adjust intensity from there. But stick with the 40/20 structure no matter what. So as you can see I was able to complete set 1 at 100% but it nearly killed me. Ended feeling like I’d just completed a Ramp Test. With the long rest interval I was able to start set 2 at 100% again, but soon notched down to 97%. And while finishing that set again nearly killed me, I told myself it was only because I’d started the set at 100%. So I went into set 3 again at 97%, stubbornly stayed there and gutted it out. By the time set 4 started I was beginning to have trouble holding the target and was completely gassed - so much that it affected my overall physical feeling the rest of the day.

In hindsight I’m thinking I should have down-adjusted more than 3% and done it earlier. Maybe even have started set 1 lower and then increased later if I felt like I could handle more.

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I started to comment before that it looks like a helluva workout. FWIW I’m also 50 and 3.9 W/kg, been doing structured training regularly for a couple years, and I think I’d have similar results with this one. The closest I’ve done is Ansel Adams in Gen Build (50/40s at 135%), and I skipped a couple repeats.

Interesting that Merced +1 is right after the ramp test. The next two Thursdays don’t look quite so evil. The whole first block looks like a reverse progression :man_shrugging:

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The weight of academic opinion holds that the best adaptation to VO2max occur with accumulated work at 95% to 100% of VO2max. So the goal in any VO2max workout is to accumulate time in that condition…but you can be at VO2max at work rates that are substantially lower than 120% of FTP. See my post on the anatomy of a 15 minute VO2max interval where we talk about Billat’s work with extended VO2max intervals.

It’s not a bad idea to start those three minute intervals harder than you think you can go & adjust the power level down throughout the interval while keeping your HR in that 92% - 95% range.

Merced…same idea, workout structure…the rest period is a more integral part of the overall workout. If you want to adjust power level in Merced, fine. Crank it up on the first interval & adjust it down throughout the set. Just crank it back up for the first interval of the next set. \

The work rate isn’t as important as achieving a plateau in oxygen consumption. To me, the less power you can accumulate minutes in a VO2max condition, the better. You’ll recover better.


15 minute VO2max interval: