I’ve been tracking my FTP, VO2 max, and weight over the past year, and I noticed something puzzling. My FTP has steadily increased from 220 in September 2023 to 274 in September 2024. My weight has remained relatively stable during this time, fluctuating slightly but staying around 79-81 kg.
However, my VO2 max, as reported by my Garmin, has been decreasing, from a high of 55 in April 2024 to 50 by September 2024. This is despite the fact that my FTP has continued to rise.
Don’t know Garmin (FirstBeat) implementation but you can double-check it with 5-minute test or if you are intervals.icu user, see it from Intervals.icu power tab. For me those are close enough: Garmin continuously, intervals.icu after going through VO2max block when I actually do such intervals.
I find my garmin predicted VO2max can vary by 1 or 2 units depending what riding I’m doing. If I’m on recovery weeks or outdoor group rides, it’ll tend to fall. But trainer rides and some out doors TT’s tend to increase it (poor TT’s just maintain it).
The VO2 max displayed by Intervals.icu is very close to the number given by Garmin for September. Garmin states that the accuracy of its estimate improves with an increase in the number of training sessions, but could it be that this will still change after a full year of structured training? Or could the reason actually be that I rode more freely without a specific plan over the summer, and I’ve now started the build phase, where the training hasn’t yet reached intensities above the threshold?
Mine has varied by 13 points throughout this year as reported by Garmin. Low of 54 at altitude, 60-62 “offseason” at sea level, and high of 67 after my VO2 and FTP block.
All Garmin does is measure heart rate vs. power. So, if you come out of a VO2 block or a really hard training block where your heart rate for the same power is lower - VO2 reads higher.
I believe that it also relies on an ACCURATE measured max heart rate that has been kept up to date in the Garmin platform. Make sure you’re using an observed heart rate from something like a 10 or 20 minute test not the age based estimation.
That’s interesting, but it seems strange in my case because in all the workouts I compared, I’m producing more power at the same heart rate. For example, in the Redondo -3 workout, my average heart rate in March was 152 bpm with an average power of 225W, in May it was 149 bpm with an average power of 227W, and at the end of August, it was 150 bpm with an average power of 235W.
Have you tested and made sure your actual Max Heart rate is correct and updated? Not sure that’d be it, but I remember reading about FirstBeat where that was a requirement for the reading to be accurate.
I haven’t followed any specific test protocol, but I’ve kept the max heart rate the same in Garmin throughout the year. My maximum heart rates during intense workouts have remained at a consistent level over the course of the year.
Again, this may not be it, but I would do an actual max effort of some sort to make sure it’s correct. There are limited workouts that actually get you to your Max HR. For me, a ramp test won’t do it, a VO2 workout won’t do it, the only times I’ve actually hit mine are 100% max effort tests. Not sure if I’ve ever hit it on a 5 minute test (maybe) but I have on 10 and 20 minute tests.
But honest answer - if you want to see it go up, do a real VO2 block. Check out the VO2 Max Progression Thread and make sure you know the difference between the VO2 Max Power Zone and Training your VO2 Max - you’d be looking for the latter. When I do a block like that, then follow it up with an FTP and then maybe an Over/Under Block - that’s when I hit my max for the year because you’re actually training your VO2 Max.
Are you quantifiably faster now than you were a year ago? I would look at your PR Chart for 2-5 minutes. Have you improved? If so, I would 100% ignore this Garmin estimate. If not, I would do a Vo2 Max block as suggested above and 100% ignore this Garmin estimate.
Mine also fluctuates 1…2 points depending on the fatigue I carry that day.
Remember, Garmin states certain conditions to retrieve a VO2max measurement (something like 20+ minutes over 70% HRmax or so). Are you regurlarly reaching that?
If not, it could maybe just apply a standard decay function.
What training decisions are you looking to make based on this VO2 number?
Is this calculation (or estimate, because it’s not a measurement) even accurate enough to matter?
What does this number tell you that the rest of your power output (maybe with HR as a secondary metric) doesn’t?
To me, things like this, body battery, readiness scores, calories from HR, etc are all wonky enough that they should never be relied on and are as likely to give you false readings as they are to be accurate.
Thank you all for the responses and recommendations. Indeed, I’m definitely faster than I was a year ago. I’m not so much concerned with the absolute numbers as I am with the trends. If something is trending downward, I’m interested in understanding why.
I agree with the logic and also place value on a lot of different metrics. With that being said, I feel that VO2 max estimates are one of the less accurate measurements of fitness levels. If VO2 max is important to you, I’d get an actual VO2 max test (maybe shoot for 1 a year or more if you really want trends). For example, my VO2 max estimate between my Apple Watch and Garmin app are often 4-5 different. If it was that consistent of a calculation, they should be similar/the same.
There are fitness metrics that ARE widely accepted as accurate - heart rate, actual FTP tests, etc. If you have maintained your weight and increased your FTP, I’d be very surprised if your actual VO2 decreased. That would seem very counterintuitive (although someone may chime in with a better understanding).
I would use FTP - w/kg as a good measure of performance increase/decrease, and also comparing similar/identical longer/endurance rides of current, to past periods. If I can ride an identical route a year later with nearly the same distance, elevation change, and weather, and do it with less heart rate at the same speed, that’s a good improvement. Or - if I can do it faster with more power, at the same heart rate. OR, at the same power, same heart rate, but faster (would tell me I was more aero lol). Lot’s of variables to look at there.
I would put zero value in the result, or even the trend of the Garmin Vo2 estimate. It’s there for your entertainment only.
Even if you did know your exact Vo2, I am not sure what you would do with this data, unless you got it tested on a regular basis. And even then, I am still not sure what you would do with this data.
Please read his question. He doesn´t want to do anything with the value nor does he wan´t do know his true VO2max. All he is asking is why his Garmin shows him a decrease while other fitness parameters increased.
Another possibility: HR measurement error. during higher efforts. Did you say what device you use, watch or chest strap?
Right - and many of us are saying that there isn’t necessarily a satisfying explanation, other than their algorithm to estimate Vo2 isn’t tracking in a manner that most of us would expect.
I agree with this and bring it up to people quite a bit who pay money for things like VO2max testing. A local coach acquaintance approached me about partnering with him as he now has a metabolic cart and is selling testing, told me he’d give me a commission if I funneled athletes to him. I told him rather bluntly I have a general rule about not pushing useless things on my clients for the sake of my own income, and that a simple, free, 5-min MMP field test repeated several times a year would suffice for my coaching purposes.
He was surprised by that response.
About the only thing I can think of where knowing a raw number is useful would be in a young, aspiring professional where you’re looking at what might be possible for them, and even then because the number is trainable I’m not sure how useful it would be. That said if I get a 17 year old with a 70 VO2max I might talk a bit differently with them than I do the 20-something with a 55… but for the most part knowing that specific number is very limited in practical use for the vast majority of athletes, IMO, and certainly on a one-time basis.
Off my soapbox.
My statement applies to both trending and the raw number. I would completely ignore the Garmin estimate.
