How is Sense 2 heart rate accuracy while exercising?

[Rami.Khalawi]

Hi all,

To the owners of the new Fitbit sense 2, how is the heart rate accuracy mainly while exercising? Is there any improvement comparing to the previous model?

Thanks

Moderator Edit: Clarified subject

[KB9WNS]

I have a now dead Sense, when that watch was functioning it did rather poorly on high intensity interval training.  My old Blaze does much better (still no comparison to a chest strap) but decent for moderate exercise and some interval training.  My Sense did poorly even on moderate exercise on a spin bike.  It did decent for sleep and resting but that is about it. My Dual HRM chest strap supports both Bluetooth LE (BLE) and Ant+ so it is possible for FitBit hardware to pair with the chest strap BLE.  Ant+ requires a hardware change.

[t.parker]

@Rami.Khalawi so specially for you, my run from December 8th, 18km, easy pace trail run :):

Three watches:

Fitbit Sense 2

Garmin Fenix 6 Pro

Garmin Fenix 7 + PolarH10 strap

Now a tricky question. Which one is Fitbit Sense 2? Not pink. It's orange. Blue is Fenix 7 (with PolarH10 which is a reference) and pink is Garmin Fenix 6 Pro. So now you've seen that Garmin may also suffer horrible HR reading (and funny, that this time Sense 2 tracked it really well).

I'm not saying that other watches suffer the same problems all time but it's not like they are always perfect either. Sense 2 tracks 1 of 10 exercises properly while Garmin 9 out of 10 but for me this is enough not to trust wrist HR (I believe I may be a bit extreme case of the user).

Here's another one (same setup, same colours). Race on December 4th, trail half-marathon. Additionally, I added an elevation profile as the race was very hilly:

In this case, I can't tell which one is better, whether Sense 2 or Fenix 6 Pro. Sense 2 seems to struggle more on the inclines but F6Pro managed to capture my HR over 200bpm at some point (I believe it mixed it up with my cadence). I'd say both watches delivered messed up HR. This is the reason why I don't train with wrist HR.

So now you had a chance to see horrible readings on Garmin watch, too 😉

The bottom line is that Fitbit won't fix Sense 2 the same as it didn't fix Sense. If it could be fixed, it would be done a long time ago for the original Sense.

[JerryHam]

Here's where I get the absolute worst performance - when doing a power walk on the treadmill. This is a fast walking pace with arm movement consistent with jogging. (I finished the November and December iFit running challenges and am finishing the year out with a few hiking challenges). It does better for me with running, but of course far from acceptable. Here's an example from this morning where it is so far off that FitBit shows the average HR far higher than the MAX HR from the iFit band. Left side in the image is from the iFit app (band connected to the Treadmill) and the right is from the FitBit App.

As you can see, at this power walking movement and pace (3.5 MPH or 5.6 Km/H), the FitBit is not even close and the graphs don't even seem to be charting the same thing. The real max HR was 109 and the average was 79. My resting HR is 46, so 79 is not out of line for such an easy walk. But FitBit thinks the max was 157 and the average was 124. As several of us have noted before this makes nearly the entirety of "Premium" - since much of the data is based on Active Zone Minutes which comes from HR - completely useless. 

The spikes in the iFit band HR correctly correspond to when the grade went to 15% (the gray area on the iFit chart shows the elevation and grade).

So in this walk, I should have gotten approximately 3 Active Zone Minutes (for me, FitBit's simplified version of "fat burn" zone is from 94 to 117). What I actually got from FitBit was 44 Active Zone Minutes. I did a second powerwalk / hike today as well, this one at 4 MPH and got similar results and now have 110 Active Zone Minutes for the day when I should have about 8.

During these walks, I would regularly see this:

Over 100% off! The treadmill data, again, is from the iFit Band and shows 74 whilst the FitBit went crazy and is showing 155.

[rambo2K22]

I've had a Sense 2 for about 6 weeks, replacing my second Charge 5 is less than a year (both simply died). This is my last kick at the can with Fitbit. Sadly, the Sense 2 is atrocious at tracking heart rate and active zone minutes. I've tried everything. Restart, adjust straps, adjust wrist position. This latest workout was the worst. Rower bootcamp. I could feel my heart bursting out of my chest. Heart rate was through the roof. I was sweating buckets. I was pushing 1:38 pace on the rower at 10 damper. Bootcamp was burpees, pike push up, squat thrusters, heavy duty stuff... 45 min total, 20 seconds max break. I was exhausted. Fitbit recorded max HR 112. I received a paltry 13 AZMs. This is utter garbage. The only function that seems to be ok is sleep tracking. So disappointed. I wish there were a fix because I like wearing the thing. It's light, confortable, good battery life, and I don't care for having a phone on my wrist. 

[Veritas175rgr]

It's honestly terrible, in everyday. It spikes and drops,  goes blank, doesn't record and then in general randomly adds ridiculously high resting rates.

[katieemjay]

Nope. Completely inaccurate.

[KenVa]

I solved the problem... went to Ebay and found a "new", unused Blaze for sale and for $30, I'm all set.  Back to holding a charge for 4-5 days, accurate heart rate and another band and charger to boot.  Really a sad commentary that company's old products are more accurate than the new ones.

[Paolov80]

It seems to catch up pretty Well with in oximeter when u are resting or light walking but is horrible in exercise mode.Everytime you enter in exercise mode all goes crazy.I noticed that if im resting and look at the Watch for example it tells me 80 bpm i begin a training it drops to 65 and continue all the training really really low,then stoping the exercise it raises at normal levels.Seems to me a bug in exercise mode,don’t know if they never fix this.

[KB9WNS]

The Blaze was decent.  Only downside is the sensor window is vulnerable to stress corrosion cracking by skin oil.  My fix to that was to use a layer of "Duck" brand "HD Clear" tape over the sensor window. Works excellent.  Still have the Blaze. 

[KayDT]

I have a sense 2 and it’s terrible. Says my heart rate is in the low 100s when I’m exercising hard and my heart is pounding and I can take my pulse and it’s in the 160s. @Fitbit seems to have no interest in acknowledging or correcting it. Can’t believe I spent $300 on a device that tracks my heart rate less accurately than a $10 pulse ox from Amazon. 

[Krocket]

I always had some issues with the HR monitor on my old Versa.  It was sluggish to respond and sometimes went nuts, reporting HR well over my max.  So I was looking forward to the SENSE 2 - they must have improved the technology in 5 years, right?  I was horrified to learn that it is basically unusable.  It’s especially bad on the rowing machine, but way off on the stationary bike ane walking as well.

I am quite sure this will be my last Fitbit, for I don’t expect the company to last much longer.  Too bad…