# VO2 Max Decreasing Despite Increasing FTP and Stable Weight

Here’s another thing. When they measure VO2max in the lab, they put a mask on your face and they ramp up the exercise rate. When the amount of oxygen you consume stops increasing, that’s your VO2max (or VO2peak or whatever - sports scientists recognize a distinction but it’s unimportant for this discussion).

Your body burns oxygen to produce aerobic power. It then delivers that power to the bike. But we all don’t have the same gross efficiency. Some of us are lower, some are higher.

Anyway, you can estimate VO2max from a short maximal effort. It’s not a direct measurement, it’s an estimate. If you searched for peer-reviewed literature, you could find people who’ve estimated the potential error margins. It might be +/- 10 mL O2/min kg or something similar. This is why they mentioned you can do this with a 5-min maximal effort in intervals.icu. This sort of estimation is well accepted in many other sports. But remember, the average difference of the estimate from the actual VO2max might be small, or it might even be zero. But that’s an average error, and your own VO2max might differ substantially from the estimate.

If you haven’t done a maximal effort, then your Garmin only has sub-maximal data. I know that you can estimate VO2max from sub-maximal efforts. Logically, I would expect the accuracy to be lower still.

The other thing is that there’s the concept of test-retest reliability. That is, in many settings, even if the underlying value doesn’t change, we would expect a test to produce slightly different results when administered repeatedly, just because of measurement error. We don’t know the test-retest reliability of the Garmin algorithm. It may be that the minimum detectable change is 1 mL O2/min kg. It may be that it’s more like 3 mL. We don’t know. But it’s not zero. And your VO2max estimates are within a band of 5-6 mL O2. That’s not a huge change.

And the last thing is that if you’re interested in VO2max as a marker of health, then it’s diminishing returns. Going from bad to below average is a huge benefit. Going from below average to average is good. If you are actually in the high 40s, then you’re already in good shape. Going from 40 to 50 is fine, obviously, but in terms of life expectancy or other measures of health, then you’re going to be gaining less than if you had gone from 20 to 30. If someone offered to magically raise my VO2max by 10 mL, obviously I’d want to take it, but from a “the needs of the many” perspective, you’d want the genie to find someone whose VO2max was like 10 mL O2 and give it to that person.

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How has your peak power / short duration power changed? Sometimes an increase in FTP can mean a decrease in 5s power or similar, sometimes just due to the way the power curve is fitted to the data values. Afaik what Garmin/Firstbeat do is compare your power curve (not just your FTP) to a set of power curves with known Vo2Max (from a lab), and then assign you that Vo2Max value. If your short-range power has dropped (or is untested), it might pick a power curve that belongs to a lower Vo2Max.

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Forget wearable guesstimates. Just track 5 or 6mim full gas efforts. What do you do with a vo2 max number anyway? Power is what matters to going fast

While I agree with common sentiment that knowing VO2max doesn’t matter if more direct performance related metrics are improving (FTP, TTE, etc), OP question is still justified – Garmins estimate is based on some combination of various metrics and if trend over medium period is downwards, it means something is not improving and possibly going worse (a la HR for certain power).

Two possible explanations:

• it started in May and continued over summer – maybe heat pushes your HR higher and you are not adapting to it well?
• longer less intense rides? a la sufficient volume to improve FTP but not enough intensity for VO2max improvements?
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Obviousely you would if you coach people yourself (as it sounds).
But if someone buys a Garmin he eventually does that to be coached by that product. And as Garmin decided to use VO2max as their prime indicator for your current fitness, you probably want to have this measured/estimated in the best possible way.
Telling those people to just ignore VO2max as it´s imprecise is somehow missing the point.

Oh yes, it´s imprecise. Luckily all other comon fitness metrics like CP, FTP, 5 min TTs, ramp tests etc are always very precise with low margin for error

I’m not a coach, by no way, but I’d second Kurts advice, and ignore the Garmin estimate, its too unstable and will fall or increase for no clear reason separate to your actual fitness trend. It can be a demotivator when everything else is going right and it suddenly falls a bit.

FWIW I see a similar macro trend of Garmin estimated VO2 being higher in cooler months and lower in hotter months. Backed up by the occasions when I’ve done cycling trips going from hot to cooler climates and vice versa. 7 years of data!

Possibly another factor is that I tend to do more indoor training in winter and those indoor rides also lead to higher estimated VO2. I think because they’re very smooth with no surges for traffic stops and starts, hills, matching a group acceleration, etc so my HR stays relatively low for the power.

Overall I wouldn’t worry too much about it. My N=1 is that the Garmin estimate is in the right ballpark at a macro level (had my VO2 lab tested last year and it was right in the middle of the range that the Garmin shows) but probably not good enough for tracking smaller fitness changes. I turned off Training Status as think it’s far too reliant on that VO2 number.

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Buying a Garmin does not mean you are doing it to be coached by that product, incorrect assumption. I own a hell of a lot of Garmin Stuff and have never relied on it for that and probably never will. TR and “Coaches” do that.

I’ll add another hypothesis on the Garmin. If you’re one of those people that has a pretty consistent heart rate that’s pretty predictable, predictable HRV, etc., and you have a correct max heart rate in Garmin’s software, I think it’s probably directionally correct when you look at the macro trend - i.e. not absolute number at all points of the year, but how you compare to the same point in your training cycle from a year prior. I have a higher absolute FTP this year, which means I’m doing similar Heart Rate workouts for whichever training block I’m in at a higher power. I’ve watched mine steadily climb through my VO2 and then FTP blocks, peaking a couple points above where I was a year ago, then drop a little bit as I went into specialty, racing, and then time off. Exact same trend / curve shape as I saw last year. But, my heart rate is pretty predictable and aligns with my power zones pretty consistently without a ton of variation.

With that said, it’s really an amusement metric and that’s pretty much it. FTP, TTE, and power curve tells the real story. I think the Garmin VO2 Max is definitely good for psyching out your buddies when you can tell them they’ll never catch you because of their scary low VO2 Max

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Another possible explanation: The OP’s short-term efforts are all sub-maximal from April to now. Like for me, I last did a 20-min FTP test around April, and I hit 310W in the 5-min part of the test. From then to now, in my outdoor efforts, I have not exceeded that power at the same or similar durations. It’s likely I could match or maybe exceed that effort if I specifically tried. But nevertheless, if I check intervals.icu, my VO2max estimate has declined from when I set that power record.

We gotta remember, the Garmin is not directly measuring your VO2max. It is estimating your VO2max based on efforts you do. The intensity of the efforts you feed it is key. If all the efforts are close but not equal to the maximum possible on your actual power-duration curve, then you would see something like this.

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You as well eh?

I’m not saying it’s imprecise. I’m saying it is totally meaningless. First off, it’s an estimate based off of HR data. As you probably know, HR is affected by numerous non-performance factors - heat, caffeine, stress, sleep, etc. Using something that is primarily based on HR is, yes, “imprecise”.

But the real catch here is that VO2max (or eVO2max or whatever) is a number that does not - in any way - lend itself to performance gains. It’s not actionable. It is trainable, but to what end? Is not the goal of coaching, whether by me, or Trainerroad, or Garmin, to improve performance? VO2max is not a performance measurable, so if you eVO2max on your Garmin says you are fitter but that isn’t translating to your performance… then what?

You’re better off using a power meter and conducting periodic field testing. Those can be done with Garmin products irrespective of their features, and in fact, I’d argue that Garmin’s products (Vector 3 and their head units) are among the best, if not the best in the game. But that doesn’t mean you need to use the bogus metrics they talk about.

This applies to their recovery stuff as well. My Forerunner would tell me I need 2 days of rest after literally anything. So no, as a Garmin user for everything from Forerunner, to Varia to Vector3, I summarily disagree with purchasers wanting to be coached by the product.

I would say the opposite: purchasing a product intended to measure, record, and display data, but with marketers telling you all about their great proprietary metrics (which are bogus), with the intent of it “coaching” you is an utter mistake. And that is demonstrated by the fact that this user is dedicating mental energy and time to figuring out what’s going on with a metric he or she probably doesn’t really understand in terms of how it’s estimated, and to no actual training end. It’s misleading at best, and is throwing them off of what is probably a totally fine training plan otherwise.

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Keeps me up nights.

Cycling is a contest of who gets to the line first. It’s not about who consumes the most oxygen.

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Actually, in the popular media, there’s been a lot of discussion about VO2max and its link to health. So maybe that is where the OP is going.

However, their eVO2max is in the 50s. Let’s say there’s an estimation error of +/- 10 mL O2/min kg. So, if their VO2max is actually 40, that’s hardly horrible. That’s about average … for non-athlete men under age 29.

Furthermore, remember that in the relationship between VO2max and health, there are diminishing returns. Going from 40 to 50 would be nice, sure. Is it going to gain you much in life expectancy? I doubt it.

And for all we know their VO2max is really 60. Which is nice, except that now we also know their gross efficiency is low … and I don’t think you can do much to train cycling GE once you’re an experienced cyclist.

Yes I did not cover every single use case for that number. You are right. Still wouldn’t pay any attention to it. YMMV.

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think of this in a way as if you have a house with walls and a roof. The entire “volume” of the house is your FTP, which is then limited by the roof. You cannot have higher FTP than your Vo2 Max. FTP is a sum of all your energy systems. To increase the FTP, you either have to increase the overall size of the house or build a higher roof. In other words, if FTP increases, but Vo2 does not increase (decrease based on indicators), then it is clear that your floor and walls become stronger, but the roof remains the same height. To increase FTP, you have to increase Vo2 at some point, otherwise the floor will meet the roof once you progress with your training and eventually you become a “diesel”

The change in Garmin’s estimate of your VO2 Max could be based simply on the type of workouts you’ve been doing lately, change in the environment you are working out in (getting hotter / colder), etc. Garmin is estimating your VO2 max based upon ??? And any estimation model output will be affected by inputs. Here’s a perfect example of WKO5’s estimate of my FTP - notice the big drop in mFTP 90d at the end of July, and then it goes up in September. I haven’t done a big effort that would justify the increase in September, so this increase is an effect of how WKO5 models FTP based upon the combination of the workouts it incorporates into the model. As the balance of actual Power-time peaks changes, mFTP changes

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There are two possibilities:

1. Your VO2max is truly decreasing. This seems unlikely given that you’ve told us that your performance has improved during this time.
2. Garmins estimate of your VO2max is off. This seems more likely for the same reason.

As long as you have accurate data and inputs for things like resting and true max HR, Garmins VO2max estimates actually tend to be fairly accurate, contrary to what’s been said elsewhere. There is published data on this, and there have been studies done that use Garmins VO2max estimates as inclusion criteria.

As a result, the most likely things would be:

1. You have inadequate recent data (HR, power) points recently based on the riding you’re doing for Garmin to get a good estimate. This would include issues with heat stress recently, which will make the algorithm think your VO2 is lower than it actually is (I think?)
2. There is a problem with your HR or power monitor that is slowly worsening over time (unlikely I think).
3. You have inaccurate values for things like resting or max HR (seems unlikely).

I would personally contact Garmin directly for further advice if this matters to you and you can’t get it to make more sense.

Look at you power to HR ratio - really what Garmin does is comparing them. It is very possible that due to summer season and increased temperature your avg HR is higher for the same power. Many people (including me) experience lowering VO2 estimation in the summer. Mine have plunged form 54 to 51.
But this is really only an estimation that changes - you real VO2 Max did not change that much, of course.