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9.33/9.36 has ruined heart rate monitoring!


After upgrading my my fenix 7 to 9.33 I have noticed a few odd things about the heart rate that's displayed/recorded on my watch. Here's what I noticed:

First run with the new Firmware: My old H7 chest strap sensor, which worked fine before, showed sudden drops in HR of about 30 bpm while running at a constant pace. (H7 has a fresh battery.)

I thought was just the chest strap, but then I noticed sudden mayor changes in HR with the integrated HR sensor as well, when I was just at home. Within 2 seconds it jumped or dropped by about 20 bpm.

Also, when I stand up after sitting for a while, my heart rate does not change at all on the watch. It keeps showing mid to high 40s. However I can clearly feel that it's way off for about 15 to 20s and then it starts "catching up". > Again I big jump in HR on the watch. I tested this multiple times by comparing it to the data from my H7 + old watch where it behaved as expected – a gradual increase in HR.

I also restarted the watch which didn't help and I made sure I was wearing it correctly. (I wore it the same way before upgrading the firmware.)

Before the upgrade it felt very reliable and now I don't know what to think. Has anybody else noticed something similar? Any suggestions on what to do now?



  • I always wondered the same. It is very unusual and ineficient that important topics on forum are not considered by Garmin staff for whatever reason. Some other topics are but major topics are left unanswered for a long time (such as open watter swimming, compass issues, now HR).

    Reporting bugs to garmin support and beta forums does not yield results obviously.

    Bug reports should not be redirected to different channels but collected and treated adequately by fixing issues and providing feedback on status of those bugs.

    Silence and redirection does not instill confidence or resolve issues.

  • My side as someone who either dual records with Zwift or another watch if running (Fenix 6 Pro) in parallel I cannot see any difference. I never use optical for activities but for a resting state it matches my Polar Verity Sense..

    For activities with either a HRM Pro, Polar H9 or Verity Sense I can't notice any differences for running (where where I dual record with an F6 Pro) or indoor riding where Zwift captures the same ANT+ HR steam my Fenix does.

    I should say I always disable Auto Detect Max HR as I know my MaxHR so maybe keeping this setting On, enables some smoothing or other processing?

  • Thanks for the data!

    What's the reaction time between the two? When you're sitting down for a while and it show's 44 on both devices, that's fine, but what happens when you get up/do something to increase your heart rate? Do they ramp up simultaneously?

    I should say I always disable Auto Detect Max HR as I know my MaxHR so maybe keeping this setting On, enables some smoothing or other processing?

    Turning this off didn't change anything for me. It still takes 15s+ for the watch to notice that I've stood up. (HR still goes down before it goes up) (I also restarted the watch after changing this setting.)

  • but what happens when you get up/do something to increase your heart rate? Do they ramp up simultaneously?

    So if I am active, then wrist HR is terrible, but this really has always been the case which is why I always use an external HRM

    At rest (both are the same)

    After 1 minutes fast walking indoors

    So I see lag or most likely the wrist HR just isn't tracking once I am moving, but this is no worse than I saw before, which is why for me, only in the resting HR scenario I find wrist HR useful. Otherwise you probably have as much luck with a random number generator ;)

    But I think some people are saying they have issues with external HRMs too, and in this scenario, what my Femix 7 records is no different to Zwift or the Fenix 6 Pro if both are using same external HRM.

  • If you feel you have identified a bug then contact Garmin Support and log it.

    I have yet to see any of the issues that I reported being fixed. Some of them I reported more than 3 years ago. 

  • If you have concerns regarding your watch OHR sensor and how it reads you in and outside of an activity, please reach out to Outdoor Product Support in your region.

    Please Review This Support Center article:

    The Heart Rate Sensor on My Garmin Watch Is Not Accurate

  • Hi

    It's great to see you're looking into this!

    Just to be more focused: Is there anything specific you have in mind beyond what has been provided in the thread?

    I think so far, some of the clearest examples are what J has shown here for example:

    Ive done another set of hill repeats and I've been able to replicate the same discarded data issue during rapid HR elevation that I noted in my earlier post.

    Heres the data from the Garmin:

    And the data from the Fourth Frontier strap (I've provided the EEG plot from one of the ascents where the Garmin was discarding HR values. You can see that the strap's resolution goes well beyond detecting heart rate, but also provides a pretty clean plot of the heart's activity (i.e. I have confidence that the strap is providing correct HR data to the watch when I can see the EEG plot matches the reported HR):

    or here:

    Runalyze HR graph produced from the fit file

    Connect IQ graph from the same fit file

    I will also provide the data from my test via eMail.

    If there's anyone with two Garmin devices, one older and one with 9.33 who can show the discrepancy, that would be ideal.

  • Today was my first long run with 9.33 and I noticed multiple instances of WHR glitching, which to me looked like locking on cadence, especially on downhills. When that happens the HR jumps to 15-25 bpm higher than my actual HR. Then after some time it drops back without me changing anything. 

    In the last few months I was really impressed with the WHR accuracy. I don't remember it glitching even once. I am not sure if it is the new firmware version or a colder weather, but it looks like I'll have to switch back to using a chest HR monitor. 

  • Can confirm the same. Not quite healthy at the moment thus when I jump up my HR shoots up. Just tested with HR from oximeter and watch. The first small rise in HR was caught by the watch. Then it stayed there while the HR shot up on the oximeter. Then garmin followed some 20 seconds later. This is not good at all.