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Heart Rate Accuracy Issues with Fenix 8

Coureur FR

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 in reply to R R

    not necessarily. Plastic watches weigh less and often have smaller diameter. Your newer watches or more expensive ones seem to have steel cases of larger footprints, and the sensors versions have changed over the years. Elevate v3, v4 and v5.  The v5 has more optical sensors to begin with.  Optical HRM is susceptible to interference from dark skin, tattoos, heavy sweat, hair, your wrist bone being close and pushing it away and if you jack your arms around really fast vs let them flow in balance the heavier watches may need to fit snugger, so their mass doesn't change how close they are to your wrist when you power your arm movement. As i type this i can't believe i'm having to explain the physics of light based HRM and watches but whatever.

  • 0 in reply to Supernovae
    Supernovae said:
    As i type this i can't believe i'm having to explain the physics of light based HRM and watches but whatever

    I'm glad you're having to explain this and not me this time. It gets pretty tedious to have to explain the fundamentals of newtonian physics year and year after year.

  • 0 in reply to 2529455
    • Tedious as you might think it is, it's not true. My former light fr945 had the same problem for some time but Garmin was able to patch it out and at the last firmware it was working correctly constantly. My Fenix 8 is somewhat heavier but same size, was improving in heart rate monitoring during runs but suddenly turned bad again after update about two months ago. Weather wasn't cold yet and still isn't. I always wear it tight. So Garmin needs to do proper investigation and get the firmware right. They did it before and we expect a proper working device for this price.
  • 0 in reply to rvdave11

    Hi Dave - 3 months is about the same length of time I've been encountering issues with heart rate results. I now know for sure that the biggest issue I had was Garmin auto correcting my heart rate max target to an unattainable number for me. However since I purchased the watch in the same period the speed of heart rate update seems to have slowed. Everything points to an update issue which I hope Garmin will look into.

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