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Heart Rate Accuracy Issues with Fenix 8

Coureur FR
2 months ago

Hello everyone,

I recently purchased a Fenix 8, and I’ve been experiencing significant issues with heart rate accuracy while running. The heart rate detected by the watch is much lower compared to both my previous watch (Fenix 6 Pro) and my chest strap readings.

Here are some specific observations:

During my regular runs, my average heart rate should be around 150 bpm, but my Fenix 8 never goes above 130 bpm.

During interval sessions, my heart rate should reach around 180 bpm, but the Fenix 8 still does not exceed 130 bpm.

I have tried tightening the strap to improve sensor contact, but it made no difference.

I’m very disappointed, especially since my Fenix 6 Pro was much more accurate, usually within ±10 bpm of my chest strap readings.

Has anyone else experienced similar issues? Are there any settings or troubleshooting steps that might help improve the heart rate accuracy?

Thanks for your help!

  • 0 26 days ago in reply to ivano59

    Garmin offered me the HRM PRO chest strap. That one measured ok.

  • 0 26 days ago in reply to 9036334

    Exactly, the chest strap measures ca. 30-40 bpm more than the watch.

    Now here's the thing: When I want to know the Recovery Heart Rate (after stopping the activity, press the 8 o'clock button a couple of times to get to the Recovery Heart Rate function), then it calculates from the correct heart rate and gives me a false result. Example, if the fénix 8 indicates heart beat of 120 bpm at the end of an activity, but the real rate is 160 bpm, then the Recovery Heart Rate is calculated starting from 160. After two minutes of recovery, it then measures for example 120 bpm, 40 beats slower. But as a result, it would then indicate 0 seconds, because it compares the result to the heart rate that was (falsely) measured at the end of the activity, namely 120bpm.

    I hope I wrote this a bit in an understandable manner. If you have any questions, please reach out to me.

  • 0 26 days ago in reply to Coureur FR

    Judging from the multiple reactions on this thread, it must be a fénix 8 problem. I have not heard of any other Garmin watches having the same problem. This is what astonishes me: Garmin should clearly be able to resolve an issue like this.


    By the way, I also bought a cheap equivalent watch on Temu. I wore that watch together with the fénix 8 and there I saw the discrepancy of 20-40 bpm, depending on the intensity. When I wore the HRM pro chest strap, the Temu watch showed the same heart rate. 

    What I also noticed: the heart rate is only measured wrong DURING AN ACTIVITY. As long as no sports activity is recorded, the heart rate is working fine.

    The case is clear, it is the task of the Garmin engineers to solve the heart rate issue.

    To everyone reading this thread: We should join together to officially protest against this. We all paid a substantial amount of money for this watch that is supposed to be state-of-the-art. It is not acceptable that this measurement is malfunctioning. 

    If you agree, please reply to these posts.

  • 0 26 days ago

    I have the same problem too. I am using a Polar H7 chest strap sensor and compared to the wrist heart rate sensor the deviation is way off while I am on the trainer for example. I have no idea what is going on anymore with Garmin, really. Fenix 8 is by far the worst 1200 euros spend in my life so far.I mean really over 400 firmware fixes since the watch came out? And still fixing? And now what? After everything works flawlessly (NOT) we have the subscription model? I am totally furious, and I am already seeking ways to start migrating to another platform.

  • 0 25 days ago in reply to patten67

    Ho inviato una email con il link della discussione, al supporto Garmin. Vediamo se risponde....mi hanno sostituito un Fenix 8 Solar per questo problema ma anche quello in sostituzione ha lo stesso difetto..

  • 0 25 days ago in reply to prain

    I would bet it has to do with operating the remote, or grabbing a jelly-bean or something along those lines... Grinning

    I use mine on the trainer all the time, it's reasonably accurate (when I occasionally forget my strap), like most stuff, until I do something wonky with my hand/wrist, which is why I generally ride with a strap (chest or optical arm, depending), regardless of indoors/out.  I would bet this is particularly inaccurate on a MTB ride, or similar.

    There was a time where I tried to get this to be consistent, with wrist HR, but then I realized I was giving myself more strife wondering if my HR against power was going to be accurate, etc.- I decided the trade off just wasn't worth it (particularly the new optical-arm models, which are quite comfortable, but still highly accurate, very close to chest straps now).

  • 0 23 days ago in reply to NikosA

    I am speechless about the fact that Garmin does not do any effort to solve this problem...
    @NikosA: Do you have any tips how and where to migrate the data to?

  • 0 22 days ago in reply to patten67

    @pattern67, I am still exploring ways my friend. I can tell you what I have done so far. I asked for all my data from Garmin. The process is described in Coros website support, as it seems Coros is trying to make it easier on Garmin users to migrate. Garmin gave me the data as was described by Coros and then I tried to load them in Coros training app to see how is their platform compared to Garmin. Guess what, none of the files was usuable, and I got only errors. I thought it was Coros, then I tried to upload them in Strava...The same! the files cannot be read (I am referring of course to the .fit files with all my activities). Then I tried the ultimate...re upload it in connect... Error again! So you ask your data back, but you get a bunch of files that are useless? I don't know what to think anymore. And I have downloaded the data twice just to be sure it wasn't a bad download. I then turned to Strava where I did the exact same thing (since all my activities are in sync with Strava). I got my files and then I went back to Coros. The data were loaded just fine. Although I do not own any Coros devices, I still can check their app and my data to see how are they doing compared to Garmin. The similarities are there and so far it looks good, but I am still testing. I can't of course migrate just like that from one platform to another, I am into very deep with Garmin (blood pressure, index scale, powermeter, tacx trainer, and the list goes on yes I am (was?) a Garmin fun boy). For sure I can tell you, that there is not going to be a Fenix 9 for me, even it comes with hologram stats.

  • 0 22 days ago in reply to NikosA

    @NikosA, thanks for the information, I will check out Coros and post my findings here.
    Yes, I know the feeling of being 'tied' to Garmin... Then again, I've been having Garmin Forerunners and fénixes for the last twenty years or so, starting with the bulky Forerunner 101. And I've never had any issues with my Garmin devices, up to now.
    I will also try again to ask Garmin if they know of the issue and if yes, are willing to tackle the problem. Last time I complained I received the HRM pro-plus chest strap, which is helpful, but does not really solve the problem.