V02 Max decrease from Beta 20.31

Same.  I have been fairly stable and any fluctuations have been tied more to dealing with a non covid cold than anything else.  So this is not an issue for everyone.

to many of us is an issue. I did a long run on same path with lowest HR avg on a similar pace and distance and I saw a decrease of V02 max. That is an issue. I will keep this monitored on a next race and check the pace and Vo2max...

4977680 said:

with lowest HR avg on a similar pace and distance

You cannot infer anything from average HR on similar pace and distance (whatever that means). There are too many variables at play (environment, your physical condition, stress, rest, etc. etc.).

The watch recalculate a VO2 Max after every run and the results can change by time of the day, the day, and again, depending on the conditions. To avoid meaningless ups and down, the watch smoothes out the estimates over time.

4977680 said:

I will keep this monitored on a next race and check the pace and Vo2max.

Your performance on a race also depends on many extermal and physical conditions. If your race is up to a marathon, your threshold performance will be a better indicator than your VO2 Max

Etupes25 said:

You cannot infer anything from average HR on similar pace and distance (whatever that means). There are too many variables at play (environment, your physical condition, stress, rest, etc. etc.).

But Garmin's VO2 Max estimation algorithm isn't directly based on any of those other variables, is it? As far as I know, the core of the algorithm is based on measuring pace and HR for a submaximal effort, and extrapolating that to a maximal effort based on the user's max HR. The maximal effort is then plugged into a lookup table which maps it to estimated VO2 Max.

On newer devices, adjustments are made for heat and elevation, but I don't see how things like stress and rest would *directly* influence the calculation.

For example, if I'm stressed out or I only got 2 hours of sleep last night, I might expect to run with higher than normal HR for a given distance and pace, or at a slower than normal pace for a given distance (with similar HR to "normal" efforts.) In this way, stress and/or lack of rest would negatively affect either my pace or my HR, which would likely lead to a drop in VO2 Max.

But that's not what they're saying. They're saying that their HR was lower than usual for a given route that they ran with a similar pace to their usual pace.

In other words, their performance (wrt HR and pace) on that route was seemingly better than usual, yet their estimated VO2 Max dropped.

Similarly, if I go for a long run wearing a 50 lb backpack (and I usually don't run with additional weight), this is a variable that Garmin cannot possibly account for, and it would likely cause my estimated VO2 Max to drop. But the reason for the drop in VO2 Max would still be explainable by either a slower pace than normal and/or a higher heart rate than normal.

I'm kinda curious whether they're long run route is hilly though. If so, maybe they've been bitten the zero elevation bug? If it's a really hilly route, and they've run it at a certain pace in the past with proper elevation data, if they now run it at the same pace but the watch thinks the elevation is completely flat, seems to me that would be interpreted as a worse performance than before. (Assuming that elevation changes are indeed taken into account for VO2 Max estimations.)

(However, I have noticed that even when one of my runs is affected by the 0 elevation bug, the grade-adjusted pace for any given lap is still not equal to the actual pace, which suggests that the watch does know the elevation is changing on some level. Either that or GAP is completely broken on Garmin watches.)

Etupes25 said:

4977680 said:

I will keep this monitored on a next race and check the pace and Vo2max.

Your performance on a race also depends on many extermal and physical conditions. If your race is up to a marathon, your threshold performance will be a better indicator than your VO2 Max

I don't think they're complaining that Garmin's VO2 Max isn't predicting their performance, I think they're complaining that their performance isn't predicting changes in Garmin's VO2 Max.

So in the case of a race, if they run faster than Garmin's VO2 Max would predict, that wouldn't be a cause for concern, if I'm understanding them correctly.

What would be a cause for concern is if they run a "good" race (pace faster than usual for that distance and/or HR lower than usual), and their Garmin VO2 Max dropped.

FlowState said:

VO2 Max estimation algorithm isn't directly based on any of those other variables

Correct. But your heart is responding to effort in certain conditions. Heat, elevation, fatigue, stress, injuries, etc. The Vo2 Max model on the watch takes into account some of them. In addition research has shown that gas exchanges can vary during the day, by day for the same athlete. So not only the indicator variable (HR/HRV) can be correlated differently to ventilation based on conditions, but ventilation itself can vary depending on conditions.

FlowState said:

In other words, their performance (wrt HR and pace) on that route was seemingly better than usual, yet their estimated VO2 Max dropped

Performance may be defined as how fast you run a distance. Vo2 Max is a measure of aerobic capacity and is an excellent overall fitness metric in general. Vo2 Max is the size of your aerobic engine, how fast you complete a lap on a race track is enabled by this capacity and is somewhat correlated to it. In fact, it is more a limiting/enabling/factor. Between 2 athletes with the same Vo2 Max, the one with the highest threshold pace will win every race.

FlowState said:

What would be a cause for concern is if they run a "good" race (pace faster than usual for that distance and/or HR lower than usual), and their Garmin VO2 Max dropped.

It wouldn't be a cause of concern at all, and it happens to me all the time as I see my Vo2 Max estimates go up or down after a 5kPB (up) or a HM PB (down) for whatever contextual reasons.

VO2 Max trends are all what matters, not fluctuations from run to run.

Yeah my only point is the person you're responding to seems to be concerned about how actual performance affects Garmin VO2 Max estimates (they gave an example where they clearly think their VO2 Max should not have dropped), while the points you brought up are more applicable for the opposite direction of the relationship: the predictive power of VO2 Max estimates with respect to actual performance.

For example, I don't think Garmin directly takes lack of sleep into account when estimating your VO2 Max from a run. But clearly lack of sleep would probably affect your *actual* performance during a run.

My understanding of 4977680's comment is they are concerned about the effect of actual performance on Garmin VO2 max estimates, and not the effect of VO2 max (Garmin estimates or otherwise) on actual performance.

The difference is that in the former situation, those other factors (e.g. fatigue, injuries) don't seem to be directly involved in the calculation, so differences in those factors cannot be used to explain why 4977680's VO2 Max dropped after running the same long run route at a similar pace as before, but lower heart rate.

If we were talking about how VO2 Max can predict performance before the fact, then I would agree that all of those factors would matter. But I don't think that's what 4977680 was talking about.

Etupes25 said:

It wouldn't be a cause of concern at all

Sorry, I meant in the context of the thing that 4977680 is referring to: their perception that VO2 Max estimation isn't working properly.

Etupes25 said:

VO2 Max trends are all what matters, not fluctuations from run to run.

Sure I agree in general. If 4977680's VO2 Max continued to drop while their performance continued to stay the same or improve, then that might indicate that there's a bug or something has changed in algorithm, or at least that there's something which doesn't make sense on the surface.

Personally I haven't noticed anything.

I don’t agree as if my training is same and I am performing same or even better than Vo2Max cannot decrease. The other problem is that I am getting a “non productive” activity since the  updates 20.xx and matching the drop of Vo2 Max

Regarding Sleep I never used the watch at night since my first Garmin so this is a parameter that even if is considered by Garmin is not influenced as no changes.

Ahoj moje vo2max taky klesá z 71 už jsem na 67 a výkonnost držím stejnou ale překvapující je že predikce závodu zůstává téměř stejná i když vo2max klesá pořád mám předpověď na 10k za 32:30 čekal h že když klesne vo2max tak na to bude predikce závodu reagovat 

The race prediction uses other data than your VO2 Max. Research has shown that VO2 Max is not the best predictor of race performance. In fact, *pace* at VO2 Max and *pace* at lactate threshold are better predictors. Vo2 Max has been found to explain about 81% of the performance variations across well trained athlete, while pace at VO2 Max explains more than 94%: this is because pace at VO2 Max includes running efficiency.

https://journals.lww.com/acsm-msse/fulltext/2010/05000/test_of_the_classic_model_for_predicting_endurance.20.aspx

The race predictor of Garmin also uses your recent training data (mileage, pace) to evaluate how you perform across various workouts.