How long time for Vo2max to settle?

My Garmin Fenix 5s is just about 3 weeks old, and im pretty confident that the Vo2max still hasn't settled to a correct value. Because of this my last week of workouts has been categorized as being unproductive, even if im clearly gaining fitness. I run three times a week, leaving at least a full day of rest in between, which is more than the Fenix 5s recommends me. My stress level according to my watch is pretty low at mid 20's to 30's. My weekly training load is about 700, optimal range. The Fenix 5s explanation is my training load is optimal, but i'm loosing fitness could be because my body might struggle to recover. I don't support this explanation, and i can't find any evidence to support this in the info my Fenix 5s is supplying. I believe my initial predicted vo2max was overshot by as much as 10%, which i believe is a lot, especially considering it hasn't settled after 3 weeks or 9-10 runs. My first run was a 25 minute run, 4,36 km, pace 5:44 min/km, avg. bpm 184. This was pretty much an all out effort posting a predicted vo2max of 45, resulting in a predicted race of about 23:30 min 5k. At this point i knew it was pretty fishy, considering an all out effort 25min. run netted me 4,36km i wouldn't be able to race 5k in 23:30 min. Today three weeks and 9 runs later im running 30 minutes, 5,3km, pace 5:38 min/km, avg. bpm 180 - clearly an improvement. I set three personal bests this week (being 'unproductive') longest run, fastest 1k and fastest 1mile, the last two on my run yesterday - still unproductive. My vo2max has fallen to 43, but its still to high as it predicts a race time of 24:12m 5k - my fastest 5k yet is 27.21. I believe my vo2max should be closer to 40-41, which my apple watch actually got right. I tried changing it manually in my personal settings but i guess that didn't count. I paid four times the amount of money getting this Fenix 5s, and at this point i think my apple watch series 3 did a better job. It's demoralizing spending this amount of money for a watch that is no better at calculation my fitness level, calling me unproductive. How long time will it usually take for a watch like this to get the vo2max right? My apple watch calculated after every run. One run could be vo2max of 40.21 and next run 41.00 and then dropping to 39.85 on my last run if my recovery wasn't long enough. That was a lot more constructive feedback than the Fenix 5s trying to slowly lowering my vo2max calling my effort unproductive until it finally gets it right. Sorry for a bit of a rant here, but im a bit baffled by a watch this caliber getting it roughly 10% wrong, and keep getting it wrong (though slightly less wrong every time) during weeks.

Would it have been better/faster if i slept with my watch? I suspect not, my runs should speak for them selves, and i didn't sleep with the apple watch either.

Edit: Additional info i forgot while ranting...

My first run with this Garmin Fenix 5s watch (25 minute run, 4,36 km, pace 5:44 min/km, avg. bpm 184. as stated previously), had an Aerob TE of 5,0 and Anaerob TE of 3.5 and it recommended 3 days of recovery, so the watch must have know it was a really hard effort, and it still overshot my fitness level by ~10%. I wanted to try an adaptive training program with this watch, however im not confident in the devices ability to creative an adaptive program when it initially overshoots my fitness level by 10% and following weeks struggles to adapt. How will it adapt a training plan to my fitness level, when it can't seem to find my fitness level.

0 Daniel_Ilg over 5 years ago in reply to 6502627

Have you checked out this article: https://www.outsideonline.com/2407295/why-higher-vo2max-isnt-always-better

This is what I meant by your performance being limited by too intense training

The short and intense runs are too short and too fast to improve your efficiency. You are accumulating too much lactate bc you don't train your base. Garmin's aerobic training is misleading here.

0 6502627 over 5 years ago in reply to Daniel_Ilg

Thanks, i read the article, and i have seen a couple of videos on youtube on this exact subject aswell. The article states the following:

"If you’re a 5K runner, you probably want all the VO2 max you can get, regardless of any efficiency penalty."

So the Garmin will only base my vo2max calculation based on my runs because the runs are highest ranked in that regard, and because my other workouts aren't hard enough, but i do low intensity training on the side. Cycling 1-2 hours at hr zone 2-3 or rowing 30-60 minutes at hr zone 1-2 to flush out lactate to improve recovering... and just to feel good in general.

I've read the white paper subra linked, and it seems somethings a miss. It states the following:

"As shown in Figure 4, the estimation error falls close to 5% in running already with a very short period of data, and in 75% of the workouts, VO2max has been assessed successfully after running 2 kilometers."

The figure 4. shows that the curve flat-lines after about 12km. If that has to be in one run, im far of... but if it cumulative the vo2max reading should be pretty close by now, it should have been within a week actually.

I read firstbeat sort the data collected and use only "good" data. So if for some reason the data i compare after a run like total time / total distance, avg hr, avg. pace, time before peak hr at the same pace, or in short comparing the runs as a whole experience / effort - firstbeat slices and dices sections of the runs with what they believe is good data, the runs get tougher to compare, and could lead to misleading information. I can't believe this though. Many others would have the same problem, but i guess it could be a problem with my specific route, or just plain unlucky. Never had an issue with my apple watch though. Always spot on. When runs felt good, i run fast with low avg hr, my vo2max for that run was better, and on slower harder days the vo2max would be less.

Anyway... the Garmin says im loosing fitness, but it dosn't have any explanation as to why - other than maybe i need to rest/recover. The Garmin says my stress level is low, and im recovering for longer than the Garmin advises me to. Im really confident that the initial vo2max calculation was wrong, and that it eventually will get it right - and when that happens my training status will change from unproductive to maintaining or improving.

It makes no sence to me that a run on the 20th of april, 28 min. avg pace 5:40 min/km, distance 4,95km. avg. hr 181 bpm is gets a training status of maintaining. And the 22th of april 30 min. avg. pace 5:30 min/km, distance 5,46 km, avg. hr 182. gets a training status of unproductive. I can't see how improving time, speed and distance at the (pretty much) same hr and perceived effort would result in losing fitness.

0 Daniel_Ilg over 5 years ago in reply to 6502627

I just looked it up. It took my device 2 months to come up with the correct Vo2max.

I give up on my training advise though. I'm convinced that you make remarkable progress with your kind of training. Good luck.

0 6502627 over 5 years ago in reply to Daniel_Ilg

Thanks, i guess i'll have to wait it out another month or so then.

I know in the long run (no pun intended) i wont keep improving my fitness by running 5k three times a week. At some point i wont get any fitter or any faster without changing it up. But that's not now. I'll probably keep improving for another 4 weeks before i'll need to change my schedule.

As stated in the white paper by firstbeat, the vo2max is calculated by speed/hearthrate (given some other factors like age and gender) so in the same week running faster at the same hr bpm, would cause a rise in vo2max - which was not the case on my watch, it actually told me i was declining, which leads me to believe than the initial vo2max calculation for some reason was quiet wrong.

0 Former Member over 5 years ago in reply to 6502627

I had a very similar experience to you Originally it used the default heart rate (which was a bit low) then it increased it on auto to a level that was too high. This had an impact on VO2max (which inreased), but it also meant I could never reach any anaerobic threshold's and my load measurements were low. After doing a really hard set of hill reps only to get- no anaerobic effort- I switched to manually setting a value for max HR. This now gives a much more sensible data set across the board.