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

[mix123]

It looks like my suggestion to fix the heart rate was removed..

So here is data from a Nordic Ski. Red is the Sense 2. Green is a Wahoo Chest Strap. Purple is a Scoche Rythm+ on my left wrist. The Sense 2 data is so far off it's useless.

[mix123]

For the next test I looked at fitbits help page about heart rate accuracy. I moved the watch up my wrist two fingers from my wrist bone. Restarted the watch. There really is nothing else I can do. Did 1hr 45mins spinning. It did much better but its still very slow to react. Too slow to be useful for anything where your heart rate moves around. It can't get the peaks right unless you stay there for an extended amount of time. I think for general day to day walking around etc it's probably pretty close. Red is the Sense 2 the pink is Wahoo Chest Strap. It gets it in the ballpark but you can see how it misses the peaks. I think a Garmin watch is in my future.

[t.parker]

@mix123 it's not a delay, your data points aren't aligned properly. Different devices may skip some data points (Fitbit doesn't always sample every 1sec) and you need to align by timestamps. Otherwise, you'll see the such drift.

[mix123]

Either way the peaks are missing from the fitbit data. 

[t.parker]

@mix123 here's an example of how alignment affects the readings (as usual, orange is Sense 2, and Blue - PolarH10):

Interestingly is that this Run is one of not many runs that Sense 2 did quite a decent job for very intense training (that occasionally happens but it had happened with Sense, too). I picked this particular run from my records to show that it's not the rule that Sense 2 struggles with high and rapidly changing heart rates. For the wrist sensor, I think this result was acceptable. The Bike, as usual, is totally wrong again (I have not a single record of correct HR during cycling). Anyway, look at the Bike "not aligned" picture. The data points end much sooner. It means that Sense 2 really struggled with obtaining the heart rate and skipped plenty of readings. Hence, placing data in the right domain is quite important when presenting such a comparison. We know that Sense 2 HR is exceptionally bad but we don't need to artificially make it worse 🙂

[JerryHam]

Normally for me during runs or walks on the treadmill the Sense 2 overestimates my HR by a LOT (for example the FitBit reporting an average HR that is higher than the real peak HR). Today I tried it with a Tonal workout (Tonal is a resistance / cable machine). I used the same iFit band that I use on the treadmill, this time connected to Tonal instead. This was a weight workout and not HIIT. FitBit Sense 2 dramatically underestimated HR on this one. Funny that the same device can be so consistently over on one workout type and under on another type. I've seen other reports of it being way under on resistance workouts so I imagine this is consistent too.  

[t.parker]

@JerryHam the more movement required the worse results are. I think with running and walking Fitbit has the easiest job to do but most other sports create a problem. On original Sense, the issues were exactly the same. See for example a session of badminton (orange - Fitbit Sense 2, blue - H10):

Several times I looked at the watch and saw "--" which meant it struggled with reading my HR. I usually wear Fitbit on my right arm but swapped my Garmin and Fitbit this time as I play using my right arm and this could affect Fitbit's readings (it wouldn't affect Garmin's as anyway it was paired with H10 on my chest).

Now, if I align the data by data points the I see Fitbit data ends prematurely:

Above means that Fitbit couldn't track my HR for almost half of the time (H10 captured it every 1sec, I verified that). There are many data points missing in the Fitbit readings. Watch on the left wrist shouldn't really have much trouble reading my HR (not much is going on with the left arm during badminton).

[rajat1048]

The Apple watch has better HR sensors compared to sense 2. In fitbit i guess they have hardcoded its HR range for most of the exercises. Its highly unreliable and i have stopped wearing it bcoz of trust issues.Even my 20$ pulse oxymeter gives more correct HR results compared to this crap.

[KenVa]

In the early years of Fitbit, it was rated as one of the most reliable HR monitors.  When I bought [temporarily, as it turns out] the Sense, it didn't even to think to look at HR accuracy.  After all, how could a company that had the technology to make a reasonably accurate HR monitor lose that capability?  Well, congratulations Fitbit you managed to update a product to make it worse.  Oh, and not to be overlooked, I never was able to get the oxygen saturation monitor to record accurately either.  I still have my old Blaze which I am satisfied with but for it requires more frequent charging than in the past but I will sacrifice some battery life for HR accuracy all the time.

[TLinkins]

The Quantified Scientist has released his review of the Inspire 3 and it actually outperforms the Sense 2 (and Versa 4) in terms of heart-rate tracking accuracy.... this is embarrassing. What is Fitbit doing?

[talltimbers]

Here's a HR graph from my run today wearing a Fitbit Sense 2. Every previous fitbit watch would put my workout heart rate between around 150. Is something hard broke here?

 

[FloppyDrive]

Tried the Sense 2 with a rowing machine against a Polar H10 chest strap... 

[sgbednar]

It seems mostly random to me.  While the resting heart rates seem to be mostly accurate, any activity seems to set it on a crazy path. My exercise is moderate, since I'm 73 years old, but I'm getting heart rate spikes (like 115 -125) for sedentary activities like brushing my teeth or loading the dishwasher, while much more strenuous activity that causes me to breathe hard and which usually gets my heart pumping results in HR readings in the 80's.  Zones are no longer meaningful, as the only zone activity the device is recognizing is the the random spikes that happen here and there.  That throws all of the recommendations off, because it has no idea how much exercise I am getting or what my heart rate is.  The only data I am getting that appears to be OK would be the steps and sleep.  Anything based on moving heart rate is garbage.  I am waiting for a replacement.  I hope it is better.  If not, I am probably done with this thing.  

[JerryHam · Accepted solution]

I doubt a replacement is going to help - only because it seems that anyone that takes the time to check the results from the Sense 2 gets similar bad data. For me, I get a huge spike - today up to 165 - while doing my warmup walks before my runs. After 5 minutes or so, it settles down and mostly agrees with reality. Sometimes it will go "nuts" again and go really high during a slow run for a few minutes, then come back and track correctly again. The worst I have seen was sitting on the couch the other day when it said 145 for two minutes. I'm 55 with a max HR of 165 and 145 is sweating, breathing fairly hard, etc. My resting HR is 47. Two minutes later it said 50. Still on the couch, still just relaxing. It is either the same or maybe a bit worse than the original Sense 1. It is really just a watch with a step counter that shows texts and notifications. The rest is not accurate or precise enough to use.

[KenVa]

The silence from Fitbit on this thread is deafening and quite telling.  No denials, no acknowledgment of the issue, no proposed fixes, just silence.  "Talk to the hand."  Quite the business model they have now, sell fitness trackers that don't accurately track heart rate.

[KB9WNS]

It's clearly obvious that FitBit has gone to the lifestyle/fashion market and left the athletic training and fitness market.  Much more $$$ in the fashion side of things.  Us athletes expect high performance and functionality.

[t.parker]

@KB9WNS about that I don't think athletes were ever a target audience for Fitbit. The sports tracking on Fitbit hasn't changed since I owned Charge 2. They added crippled version of swim tracking and now number of new labels but there is no any features helping athletes to train, no new metrics, no analytics tools. You can revert back to Charge 2 and there will be no difference in the way sports are being tracked there. It's just a simple activity recorder. It was basic then, it is basic now and to be honest, my requirements in that area are much higher than just accurate HR 🙂 I don't have expectations that this will change as it would require totally upgraded app, watches and backend. And yet, Fitbit can barely address existing bugs... If Fitbit wants to address health and lifestyle then that's fine but even in that it drops constantly ball 🤷‍:male_sign: One thing is sure - Fitbit isn't designed for athletes.

[KB9WNS]

I used a Blaze for 2 years with excellent results.  Still have it and it does surprisingly well against a Garmin with chest strap. My main complaint with the Blaze is the poor choice of HR window material which is susceptible to stress corrosion cracking caused by skin oil.  Found that applying "Duck" brand HD clear tape over the sensor window protected it and improved the accuracy.  Big plus on the Blaze is that it is held together with 4 screws and is serviceable.  

[t.parker]

@KB9WNS majority of athletes, when their training involves HR zone training will switch to the chest strap anyway. This is why we don't hear many complaints about other brands - because users have alternatives to use external monitors (and other sensors). I've been using Suunto Spartan Sport WHR Baro and it's probably the worst optical HR in the world (worse than Sense 2 - yes, it is possible :D) and yet, from an athlete's perspective that wasn't really a big issue as I either used chest strap or armband sensor for training. I've been using that watch for a little over a year and the reason why I switched to the next one was not HR but the fact, I wanted better in-watch navigation and I couldn't connect my bike speed and cadence sensors (it was limited to a joint speed/cadence sensor and I had two separate ones so I could connect either speed or cadence, not both - stupid design). Otherwise, it was a good watch for sports tracking (and very durable which is important to me during rock climbing). Wrist HR didn't matter at all (in fact, I turned that off entirely, it made the battery last 2-3 weeks). Then, with my next watch, it took me a few weeks to even try the wrist HR because I continued exercising with a paired chest strap. On Fitbit, there is no such choice hence there is a lot more backlash. I wouldn't even bother to post all those comparisons if I could pair one of my external HR monitors 😄 I was always saying (and sticking by it) that the wrist is probably the worst possible place on a human body to wear a heart rate monitor. I see such issues on Suunto, on my old Garmin Fenix 6Pro and now Fenix 7 (this one is quite good although struggle with higher HR readings, too). Some inaccuracies are unavoidable. Even Apple Watch isn't 100% perfect. There is only one way to solve this problem but Fitbit ignores the obvious solution. Let's assume that the current line of watches isn't suitable for external sensors from a hardware and/or software standpoint. But then, the Fitbit app could successfully establish such a connection and eventually, override HR (and send the readings onto the watch in real-time during activity so the user can see it). If apps like Zwift, which runs on mobile phones/tablets can connect to a number of sensors over BT/Ant+ (HR, bike trainers, power meters, anything) then I see no reason why the Fitbit app couldn't do it either 🙂

It's not accurate HR that makes the watch suitable for athletes. Athletes usually understand pretty well wrist HR limitations. Accurate HR is a must for some basic features but as long as the watch supports external sensors this is a secondary issue. Fitbit doesn't understand it.

[Rami.Khalawi]

With all respect to you bro, but I can't agree with you. I have had apple watch 4 & 6, Garmin Fenix 6x pro, Huawei, Samsung 3, 4, and now I have garmin 7x pro and never faced any issues related to the heart rate. I have seen this issue only on fitbit sense old one.

With regards to Sunnto watches, I never tried these watches but yes you are right, I heard that there is an issues related to the HR.

I have made many comparisons between the watches and watches with chest HR monitor, and frankly speaking, the difference between the chest HR and other watches is barely noticeable. 

But when it comes to fitbit, oh its really a nightmare. 

I was really planning to buy fitbit sense 2, but with these feedback from the users I can't step forward. 

Fitbit really need to slove this issue as it's well known issue on the old sense.

Thanks,