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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 believe this is a new Firstbeat piece that was introduced in the first alpha whereas the watch is trying to estimate your maximum HR from a decidedly submax effort. How they do that I don't know... Perhaps same was Polar is trying to determine your VO2 Max from HRV during their fitness test at rest.

    For me the watch estimated 181 on sub-150 runs. I'd say my max is probably between 179 and 180 given what I see during heavy sessions and my LT HR. So, the guesstimate isn't far off. Who knows? Maybe I'm not pushing hard enough? "

    Is this something that changes my own HR settings or just some fun information piece? Asking because AI guesses don't work at all for me and I don't want to lose my manual settings. My watch thinks my Lth is at around 189. It's lab tested at 165ish though. The confusion for poor little tech stems from all my runs being above Lth due to a medical condition. I don't want to know what maxHR the watch would come up with.

  • Is this something that changes my own HR settings or just some fun information piece? Asking because AI guesses don't work at all for me and I don't want to lose my manual settings.

    I think the watch never changes LT without a prompt and confirmation from the user. At least, I have never seen it done though I get my share of auto-detected LT changes. For max HR, you can manually disable auto-detection, which presumably should disable this new submax auto detection as well (User Profile > HR > Max HR). As long as your zones are based on LT or max HR, they shouldn't change automatically either.

    Beyond that only Garmin/Firstbeat would know.

  • Thanks you all for the replies and new data!!

    Which is normal. Heart rate always lags behind effort, at least 15-20 sec.

    I don't think this is normal. And as I said, it used to be better. That's basically what made me realize that something weird was going on. It used to react quite quickly to my effort. Now it just does nothing, sometimes even drops to lower HRs and only after some delay, it starts catching up.

    Not clear if he's showing OHR from his watch or his watch was connected to Frontier X?

    That's true. But I think J had an earlier version of his post where it was already mentioned that it was the same data, but then edited it. Thanks J for clearing it up! Slight smile

    I'm only seeing this issue when performing HIIT workouts with rapid increases in heart rate. Steady state and even hard trail runs are fine.

    This could well be. I'm not sure. My (highly subjective) perception is that it's something that is always there. It's really just a delay. To me it looks like it's just more noticeable with rapid increases. That's why I tried to match the data exactly in my earlier graph. Garmin is always too late compared to the M400.

    In brief, Garmin apparently recently made the floating average period at processing the HR signal longer than it used to be

    This would actually fit the observation quite well.

    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.

    Thank you for the new data. I think this makes it very clear that something is wrong here.

    In brief, Garmin apparently recently made the floating average period at processing the HR signal longer than it used to be (and not only at F7, but also at Epix, F6, Instinct 2, and probably elsewhere too). I assume they did it to cope with frequent problems of recording double beats, leading to the false detection of the max HR, and corrupting zone tables, LT, VO₂max, and other metrics. It was frequently complained about it here on the forums too. Unfortunately their solution leads to a great lag, and to the flattening of the graph.

    Please report it to the Support! If Garmin does not get a lot of negative feedback, it is unlikely they would change anything, because they consider the change an improvement.

    Thanks for the additional insights. I wasn't aware of these issues before.

    It makes sense that Garmin try to improve something here, but as you point out, their solution seems to have made it worse instead.

    I also wonder why there aren't more people complaining about this. Maybe it's too subtle and one really has to look at the data or observe HR and realize that it doesn't make sense?

    Can someone from Garmin comment on this issue, please?

    The most fundamental feature of any sports watch has gotten unreliable in the latest update. WHR and external HR sensors give inadequate results. Garmin should be all over this!

  • So, my upgrade (for F7X) finally came two days ago. Today I did a 1 hour bike ride, with both my F7X and the Edge 1040 mounted on the handlebar.

    For the first ~20 minutes, I looked at them a lot, then I stopped because it didn't make any sense to continue so - they were 85% of the time identical, and the rest 15% at 1 bpm difference. Whether this was starting from a stop and getting from 90bpm to 125-130bpm within 20 seconds (with a clean ramp-up), or starting a sprint or a climb (130/140bpm to 165bpm), or going all out, or even while my heart rate was decreasing.

    So at least I can say that with a *Garmin* chest strap (an old one, neither BT nor run dynamics), the F7X with 9.33 behaves exactly like before - it is identical with the readings that my Edge 1040 get. I don't know if the problem is with a specific brand of heart rate straps, or with all third-party straps - but with Garmin own ones, it looks this work fine.

    I didn't save the F7X ride (since I don't want duplicates in my account - even if you delete afterwards, some stats get broken), but it was also not needed since I never saw them more than 1bpm apart. And this is the HR graph from the Edge 1040, on flickr: Screenshot. You will see that the HR ramps up very well/linearly with power (but not the same slope), and it reacts well to start-stop-start again scenarios - see around 8 minutes.

    I will probably do the same with a short ride just with the F7X, but from my side - this is a non-issue with _my_ watch and with _my_ chest strap.

  • Am I understanding this correctly ?, you are complaining that 2 devices are measuring your heart rate and 15% of the time they are 1bpm different ?

    Whats the problem with that ?.

  • Huh? I'm not complaining. I'm saying for me, the question in the title oof the thread - has 9.33 ruined heart rate monitoring - can be answered by "no, it hasn't" (for me).

  • Thanks for your info! It's good to see not everyone is affected.

    So, problems so far seem to occur with 3rd party straps or with the F7's wrist heart rate monitor.

    I will probably do the same with a short ride just with the F7X

    This would be interesting to see!

  • Still no comment on this from Garmin. Anything?!

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

  • There are clearly people from Garmin on this forum. What's their job on here if not to look for potential issues etc.? Make sure we don't swear??

    It would be very easy for them to acknowledge an issue here. Or ask for more data. Anything really. But like this it's basically a big ol' "we don't give a ... ". Sorry if I'm wrong, but after almost two weeks it surely feels that way.

    Also I just tried contacting support on the phone and wasn't able to get through and gave up after listening to music for 35 min.