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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 ran today with HRM. Though it might be some cleanness issue (washed it in tepid water) or battery problem in HRM Dual (replaced it to new one, BTW it showed OK status on the watch and 85% on iPhone before replacing - after exactly the same, so this 85% seems to be fixed). Checked if the strap is tight enough Went for a run today. Here is what I got:

    So again, during the fast paced segment its going down and raises on cool down. What is more interesting, I checked respiration rate chart as well:

    This is all screwed up and does not make sense at all. Plus I lost all trust in what Fenix 7 is measuring. I think that given the money I paid for the gear it is totally ridiculous.

  • Plus I lost all trust in what Fenix 7 is measuring

    The Fenix 7 isn't doing any measuring....

    I must have missed your post where you provided evidence ruling out an issue with your HRM belt?- there is an issue here for sure, but I am 99.9% certain you just have a faulty strap.

    If you want to make an extraordinary claim, the onus is on your to provide the evidence to support it.

  • That doesn’t explain the weird behaviour while measuring with the wrist sensor. If it worked correctly I would risk spending money again on a chest strap. Plus for me it weird, that the faulty behaviour happens during higher intensity

  • That doesn’t explain the weird behaviour while measuring with the wrist sensor.

    Since you own the HRM Dual, if I understood correctly, you can verify whether it comes from the HRM strap. HRM Dual can be used also standalone with a number of phone apps. Install one, and record the same activity simultaneously through the F7 (connected over ANT+), as well as with the phone app (connected over BT), and then compare the results.

  • So we know frequency = 1, being we get one sample per second. I do not believe the frequency has change between software versions. You should also be getting the CSV data so that it can be properly plotted. Any differences in start time between the two can be removed by adding or subtracting the time difference to one of the graphs time axis data. This will push the data left or right depending how how you do it. 

    You can also overlay them by removing the amplitude offset between the two at time=0.

    Not saying or saying the software is causing poor OHR behavior...but it isn't a sampling frequency issue.

    edit: just realized Michael's post was a month bad.

    Also I think users should be allowed to pair an external HR strap to the watch for anything they want. Whether it is everyday tracking, sleep tracking, etc.. OHR in general is not a precise measurement and when erratic behavior...which we would classify as random errors. System errors can be removed with data processing if someone wanted to. Random error can't be removed, and that is what a lot of OHR runs into when you use it for anything but sitting at a desk and walking around your house.

    If I wanted to really take a look at my sleep without going to a clinic I would want to use my watch, and I would want to be using a chest strap. I shouldn't need to start an activity to utilize a chest strap. Even Apple of all companies allows this.

  • What about some more *** HR data? Not during an activity, but just everyday use.

    first peak: walking to station
    second peak: walking from station to doctor
    third peak: walking from doctor back to station
    fourth peak: walking from station home
    thingy marked in red: exercise test that took longer and resulted in substantially higher HR than the walking. Yeah.

  • In my case, heart rate measurement during the day works tragically. Previously, everything was fine, now during each walk F7 shows a heart rate of around 130 bpm. Then I measure my heart rate with my hand and it is usually between 60 and 80, while the watch shows, for example, 130. What is the worst, such erroneous data are presented for a long time. I have already learned to take my watch off for a while, and after putting it on, heart rate is correct, eg 80. Unfortunately, after some time it starts to show 120, 130 again.

    Below is a screenshot of a slow walk, I looked at my watch frequently and after the first heart rate increase to false readings, I took my watch off for a while. After wearing it, the heart rate was displayed correctly, but after a while it was the same again.

    After buying the watch, on the older versions of the software, the heart rate measurement worked correctly.

    Additionally, MoveIQ often detects the walk as an elliptical cross trainer.

    More examples of slow walks:

  • This clearly illustrates the obvious - HR was messed up by software update. It should be fixed urgently (reverted back to previous) instead of "looking into it" 

  • Today's walk. I only put on fr955 for a walk, the earlier readings in the chart are from a different person.

    15 minutes after starting the free walk:

    (f7s and fr955)

    15 minutes later and after switching places on hand:

    (fr955 and f7s)

    After turning on the heart rate widget, sometimes the readings go back to normal, other times I have to take my watch off for a while.