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.

  • Hi

    1. VO2MAX calculation is not also incorporating your last run but it uses your recent history. So the Vo2max has a memory. This takes a while to adjust. So there is no chance that it directly goes from 45 to 41.

    2. The determinants for your running performance is based on Vo2max but it's not the only driver. Running economy and performance at lactate threshold are also part of your performance. Since your Vo2max indicates a faster time, running economy and/or lactate threshold performance must be underdeveloped. Since you train pretty intense, I would say it's your running economy, if I have to make a guess.

  • Thanks for you reply, i updated my original post, while you replied, so i added some info at the bottom.

    I believe im getting fitter on all fronts, my watch think my fitness is getting worse, because it thinks im fitter than i actually am.

    Running economics - i found this description "measures runners' energy utilization when running at an aerobic intensity". The last three runs was 30 min. long. Pace was about the same, but my avg. bpm declined, resulting in Aerob TE 4.3, 4.2 and 4.1 on the last run. I would assume that when running the same distance in the same amount of time but with lower avg. hr and a lower Aerob TE score, is evidence fitness is getting better?

  • Thanks for your reply. As i read it; the 30 days described by Garmin is not as long as it takes to get an accurate vo2max reading. It will create an estimate the first time you run (20 minutes or longer at 70% max heart rate.) All my runs will meet this criteria, and should update the vo2max accordingly with every run activity.

    Garmin describes the run vo2max to be the most accurate and hence a vo2max estimated by a run activity will be on top of the hierarchy for 30 days - only upgraded the next 29 days only by other run activities and not by walking. If however my vo2max was first set by walking, the vo2max would still update after a run activity within 30 days because it is considered more precise.

    Edit: Garmin states:

    You record a Run Activity with GPS (#1 in the list) which generates a VO2 Max Estimate on May 1st. That reading will display in Garmin Connect and will only show updated readings with additional Run Activities with GPS for the next 30 days. Other activity types in the list (2 through 6) will only update the overall VO2 Max Estimate if the May 1st activity is older than 30 days because Running is at the top of the hierarchy list. 

  • If you own your watch 3 weeks and you train 3 times a week, than there are 9 data points for performance available. Please be patient, train additional 3 weeks an you'll see more accurate VO2max.

  • Maybe this post will help you: https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-5-series/217770/vo2-max-and-race-pace-disparity

    And your 30 minutes runs with this aerobic impact are not helpful to close the gap between prediction and actual performance.

  • Thanks for reply. So i would need about double the amount of sessions than i have = 18 runs about 500 mins. total. I can appreciate that Garmin uses a more general vo2max, because your general fitness wont change a lot over the course of a run or two - i guess that's what the training effect from every run is for - where as apple watch just updates the vo2max every run, which would cause the Garmin to have a greater resolution as it splits the Aerob and Anaerob, where as the apple just combines the total fitness into vo2max. Im still a bit confused about it taking so long to adjust though. Does the Garmin couch not use this vo2max in adapting the training plans? I see there's a 5 min. benchmark run before you get a program, but there's really no way that 5 min. benchmark will be able to measure my fitness level better than the 500 min. needed by the vo2max? Sorry if im being a bit sceptical.

  • Thanks for your reply. I didn't get a lot of help from that thread unfortunately.

    I do realize that running 5k three times a week won't massively increase my race time. I would use intervals, hill repeats, tempo runs and coordination training to achieve a faster race time. When i started running again 8 weeks ago, after 4-5 years break from running and exercising, my goal was running 5k three times a week. I wasn't able to run more than 1.3k before i was completely knackered, knee pain and shin splints almost made me quit lol, so i decided to create and follow a running program. Now im running +5k three times a week, still at a pretty hard effort but its getting better every week. Im able to run further before my HR starts to rise above HR zone 3 (at the same pace), im spending less time in HR zone 5, and if i hit +180bpm im able to recover below 175bpm by lowering my pace, something that wasn't happening 4 weeks ago - once i hit that 180bpm i never recovered i just had to bite the bullet till the end. Im even running faster pace now, at lower perceived effort and hr.

  • If you want a deeper look into the calculation of VO2max

    https://assets.firstbeat.com/firstbeat/uploads/2017/06/white_paper_VO2max_30.6.2017.pdf

    (Firstbeat develops the training software for Garmin devices)

  • Thanks! I will definitely read that :-)

    I was aware Garmin uses firstbeat software, but i didn't know of this more elaborate documentation.