Heart rate inaccurate on Fitbit Sense

[Cameronoates]

Hey 

is anyone else experiencing huge heart rate inaccuracy during exercise with the sense? 

During exercise with the sense it won’t ever get above 120bpm for me 

but if I use my charge 4 during the EXACT same exercise my heart rate is between 145-170bpm in the cardio zone 

It’s extremely disappointing and I don’t want to have to switch to my charge 4 everytime I exercise to ensure accurate heart rate 

defeats the purpose of having the sense 

seriously one of the most frustrating experiences I have ever had.

Moderator Edit: Clarified subject

[Monikalew]

Yes, they are not cheap. I was not able to see these comments when I researched reviews .  Expensive for only randomly being accurate 
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[Monikalew]

Was it accurate when you worked out hard?  And for resting?  Mine still does not always relate to the highs.  Was it an automatic update?


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[Tdif]

I know I will give u an example the activity part says my heart rate was
115 at 12/35 am when I go to my sleeping heart rate it is not there also I
haven’t worn it all mornjng but apparently I did 49 min of activity and
heart rate at 138 lol so that in itself is completely wrong and frustrating
I will be going back to the Apple
--

Moderator Edit: Personal info removed

[pratik49]

Hi Silvia This is a known issue with most of the Sense and Versa 3 devices. It was confirmed by your support. The support says there is no timeline on fixing the issue but it's clearly affecting a lot of users. In my case this is my 5th Fitbit device. I compared my numbers with my HR strap. My HR strap shows numbers around 170-180 but somehow my Sense cuts off on a 160 upper limit and drops down to 90-100 range. This is clearly a bug which is affecting users since like more than 6 months and Fitbit is doing nothing to prioritize it. I am luckily in my return window and have requested a replacement from the seller. Do let me know how I can contribute and get this issue prioritized to be fixed. I bought the Sense because it's your best device out their but I am disappointed with the support for the device. If you cannot provide a solution atleast give us users some alternative. The support person simply hung up the chat saying there is nothing he can do about it when I was helping him give the repro steps of the issue. Will be happy to share the chat history.

[pratik49]

It looks like they have setup some kinda upper threshold and someone fat fingered it in the code. My HR also maxes around the same and drops down to 90-100 range

[SunsetRunner]

This is also affecting a Sense bought on Nov 18th or 19th and received the next day. I had been using an Alta HR since 2017 or 2018 and I know what a 140 vs. 170 heart rate feels like and routinely hit 170-185 on my intense cardio workouts - hiking, spinning, and elliptical. I know that the wrist-worn HRMs are not great with weights and I've noticed the Sense struggles there significantly.

But worse, on cardio, I've done two elliptical exercises since I received my Sense and my HR has barely crossed 145 and kept dipping into the fat burn zone even as my HR in my neck was going at 160-165. The elliptical machine even registered a 164 while holding it while the Sense said 141. I was able to get it to jump up to 165 by pushing all out max on the elliptical for a minute and I know my max HR is about 192 while doing cardio. So it seems it's 20-30 BPM low consistently. 

Is this problem ever going to be fixed on the Sense or is it a hardware issue with the HRM inside? I bought the Sense to use for fitness and sleep tracking; all the notifications/smartwatch stuff is ancillary for me. Do I just need to go get a Charge 5 instead and send the Sense back? This is a huge disappointment for a $300 piece of technology that is the flagship item.

[Deetee20]

I haven't seen anything on this forum that addresses this problem.  I had a nearly 60 minute HIIT, mostly cardio workout where I was genuinely gasping for breath and my Sense only reported "below zone" and calories burned were significantly less than previous similar workouts with Ionic.   Sense is a lot of show.  No Substance.  If I could get my Ionic to charge I would use that over Sense.  EXTREMELY DISSAPPOINTED with Sense.

[Tgisele]

@Deetee20  All of us on these threads feel the same way. 

[t.parker]

Just one more comparison. Bouldering session (indoor climbing). I took Sense first time to see how it would deal with this kind of activity. The pattern is simple. It's usually anaerobic activity (like weight training) with spikes during each climb and resting periods between climbs. Fitbit activity was tracked as regular "Workout".

Sense - orange, PolarH10 - blue. Looking at PolarH10, one can count spikes to tell how many times I have climbed. Sense is nowhere near that. This affected averages and AZM. Fitbit gave me 32AZM while it should give 79AZM. The avg. 103bpm, while it should be 119bpm. Again, I'm curious whether and how this will affect DRS.

[t.parker]

And another one. This time morning trail race, 21k, quite demanding due to elevation:

Fitbit (blue) and PolarH10 (orange)

In this particular case, I verified also PolarH10 data against the power meter and elevation to make sure it's a good reference (I look at patterns of ascents using elevation, power, and HR to validate HR).

Sense experienced usual issues and I believe the nature of the trail run may have added more noise. It detected the highest HR 186 which isn't true (but my cadence was 186, probably that's why). Although, in the past, I ran trails for which Sense was almost spot on with PolarH10 so I can't make it as a rule that trail = wrong readings. AZM should be 222 and Sense counted 221. This is because, despite all the randomness, the majority of data stayed in the cardio/peak. Sense gave me an average HR = 161bpm but correct data indicates that it should be 172bpm.

AZM difference is only 1 minute and the average HR difference is 11bpm (although, I find it hard to pick any part of the graph where Sense would be accurate - there are maybe 3 short segments). The second one could be significant if it's an average of the whole run. I didn't count standard deviation though but on the chart, it shows as quite significant as this data is pretty much all random.

At least the race was really nice (and cold ;)) That's typical surface but I don't think it had anything to do with adding noise.

[MrMogo]

I'm a long time user of Fitbit; many watches, recently an Aria scale.  All the features generally work well.  Sometimes there can be glitches but starting the watch over (pressing button for a long time) generally works.  One thing that is CONSISTENT without fail is how the heart rate monitor fails during more rigorous exercise.  My start-out regimen consists of 30m on an eliptical machine followed by various manual exercise (abs, kettle balls, weight machines).  Without fail, the heart rate monitor is easily 30-40+ bpm lower than what the eliptical machine says.  When I'm at 145-150, my watch says 80-90.  WAY OFF.  Useless at this point.  Then when I'm doing the less rigorous manual exercise, it pops right up to my true bpm (i.e., by now maybe around 130-150.  So in my workout record, it always records a creampuff session of 30 min of 80 bpm (I might as well sit down) followed by 45 min of real workout (130-150 bpm).  A real suck when it comes to tracking calories and zone minutes, but everything else works well.  So, I keep it.  And accept the fact that my calories and bpm are VERY conservative.  I really wish you moderators at Fitbit would stop pusing that BS about wearing the watch correctly.  Any tighter and I'd get GANGRENE.

[obermd]

I wore my wife's Charge 4 last week to test to see if I wanted a Fitbit for myself.  Running the same route last week and then again today with my brand new Sense gave me almost identical heart rate numbers.  I suspect Fitbit has fixed the HR issue in the latest version of their Sense firmware.

[t.parker]

@obermd Sense sometimes gets it right.

[obermd]

Since I only run on the weekends I'll keep an eye on this.  During the week I swim a three quarters to a mile each day.  The running is supplemental for improving my overall cardio fitness and lung capacity.

[SunsetRunner]

I can show you All that there is a massive glitch - don't know how many devices involved but that is what happens. As soon as you start an activity, Fitbit back log it. See below (by the way, I found out today but it is going on since December last year, every day). During the night your heartbit is recorded normally. You can see the limit of 106. However, as soon as I walked to work, look what happened. The data were rewritten. The spike was not there in the morning between 11pm-7am but it appeared after the activity at 8-815pm was logged . And that is happening to my Fitbit since day 1. I have plenty of pix to support that. Have a look in your activities and see if impact you too. 

 

 

 

[Tgisele]

@SunsetRunner, the problem was first reported in September of 2020. Several of us have the same issues or slightly different, there is certainly a lag in the heartrate while exercising. As others have done, I compared it to a Polar and Sense was always behind and NEVER did my heart rate come close to the highest rate of the Polar.  It is very frustrating. 

[SunsetRunner]

@Tgisele I would be ok with a lag, but having the sense telling me that my heartbit was 150 at night only because 12 hours later I was exercising it's beyond imagination. I can't still believe that. 

[obermd]

I understand.  However, I can only report what I'm seeing.  I used to be a runner until I tore a calf muscle so I know what it feels like to be near the peak zones for extended periods.  My wife's Charge 4, my new Sense (which downloaded the current version during setup), and my personal knowledge of knowing when I'm near my peak cardio area for an extended period of time all point to my Sense being accurate yesterday.  This is why I wonder if Fitbit didn't fix their software in the current release.  And no, I don't think this is a hardware issue.  

Also, I don't wear my watch at night - nickel allergy - so I can't comment on the issues people are seeing at night.

My suspicion is that the software is mishandling the high and low beat rate settings.  Why Fitbit would throw away the working code is beyond me, but it appears they did.

[NeilFinny]

---

@MrMogo wrote:

I'm a long time user of Fitbit; many watches, recently an Aria scale.  All the features generally work well.  Sometimes there can be glitches but starting the watch over (pressing button for a long time) generally works.  One thing that is CONSISTENT without fail is how the heart rate monitor fails during more rigorous exercise.  My start-out regimen consists of 30m on an eliptical machine followed by various manual exercise (abs, kettle balls, weight machines).  Without fail, the heart rate monitor is easily 30-40+ bpm lower than what the eliptical machine says.  When I'm at 145-150, my watch says 80-90.  WAY OFF.  Useless at this point.  Then when I'm doing the less rigorous manual exercise, it pops right up to my true bpm (i.e., by now maybe around 130-150.  So in my workout record, it always records a creampuff session of 30 min of 80 bpm (I might as well sit down) followed by 45 min of real workout (130-150 bpm).  A real suck when it comes to tracking calories and zone minutes, but everything else works well.  So, I keep it.  And accept the fact that my calories and bpm are VERY conservative.  I really wish you moderators at Fitbit would stop pusing that BS about wearing the watch correctly.  Any tighter and I'd get GANGRENE.

---

I found the Ionic pretty accurate, it was why I upgraded to the Sense.. bad move

[Monikalew]

Thanks for your input. From things I have been reading, Fitbit was pretty good with heart rates on models before the Sense. I have the sense.  It is not accurate on the highs for me.  Reading from others it is not very accurate on lows too.  


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