I don't believe Fitbit really counts your heart rate.

[MintyFox]

I can tell you that during my workouts where I'm doing a lot of stationary exercises like push ups and pull ups where my heart rate goes very high, the Fitbit will display a resting heart rate and will not go any higher even if I wait to check for a delayed reading. In fact if I just sit here doing nothing and shake my wrist up and down, the heart rate will start climbing higher and higher and eventually cut out which it constantly does.

It seems that it's estimating your heart rate based on movement. Right now I'm laying down, my reading is 109, I'll shake my wrist for 20 seconds...now it's 125. My heart rate did not change whatseover, I moved nothing but my wrist. It's very disappointing.

[lukedga]

Guess it might depend on the model? I have a Surge and it's constantly scanning my wrist. My heart rate climbs when I'm doing pushups or squats.

[Deksam]

I haven't had that issue Fox, though I will say that when I exercise pretty hard it doesn't display an accurate reading until I stop whatever I'm doing.  It could partially be due to an estimation, but I've had fairly accurate readings after running, stopping to take a break, and checking my stats.

Sometimes it does take a while to "catch up" .. but if it wasn't taking your actual heart rate and instead just guestimating based on movement, then a resting heart rate wouldn't calculate at all.  It could guess on a resting heart rate, but  then you'd never decrease that value, which I have been doing steadily. 

It could be a defective model. You can try to do this by calculating your own heart rate alongside the fitbit in a few different conditions to really get an idea as to how accurate it really is.

[NANiAM]

I don't really take the heart rate to serious on my fitbit. I like seeing what it says but I can tell more on knowing my body. I think it's just a quick tool to look at but not the most acurate. I do agree it does vary.

[divedragon]

The whole heart rate process isn't accurate.  I'm on my second Charge HR and this one is more accurate than the first one (it died running in the rain), but still doesn't record consistently during exercise nor does it accurantly calculate my resting heart rate.  I use a variety of methods to test this from a seperate HR monitor, the heart rate monitors on treadmills and my phones HR checker.  My phone, the external monitor and the treadmill are all pretty close, but the Charge seems to top out and/or measure about 10% lower.  If I'm really pushing myself, I check the heart rate and it just shows: --

As to resting hear rate, it calculates mine in the low to mid 60's, yet as I'm sitting here, it's showing 55 and I've confirmed that with a manual count.  54-55 is pretty common for me lately, so why is my resting heart rate today at 69?  Doesn't make sense.

Yea, I'm less than impressed with the HR capabilities of the Charge HR.

[emili]

if the HR changes that much by shaking your wrist- I would say there is something wrong with your bit. I would recommend a call to the service team so they can help you. Maybe my expectations are different than most, but my HR does a great job for me. It gives me an accurate enough HR when I run, or lift or do nothing at all. I compared it to my polar strap and sure there is a difference, but not enough for me to stop using my bit. I am always on target with total calorie burn. If it is less than what I think it should be, I compare it to a previous day where I killed it and sure enough I didn't go as hard or as long. it stinks that you are disappointed with it- I would still give a call though. Best, E.

[MintyFox]

Well when you are running, its cycling up the heart rate just like when I shook my wrist but since you're also actually active, your heart rate climbs as well. Has anyone tried checking what their heart rate is now, shaking for 20 seconds then checking again?

I'd look into getting it fixed if theres a problem but I got this thing in early 2015.

[SunsetRunner]

50 heart rate, stays same with shaking..

When being ill a longer time ago, constantly was in fat burn zone while not exercising.. periods of not being in heart rate zone if not exercising, and went up to a higher heart rate with exercise and increasing intensity..

Believe it must measure what your actual heart rate is (close to), not depending on moving your arms.. then the heart rate sensors could be left out if it be depending on movements alone.. and can't be called 'heart rate tracking' then, and use for more accurate estimation of calories burned.. (personal opinion)..

Your tracker can be faulty, as @emili suggested it's possible to contact the Fitbit Support Team (Click here to contact)

Optionally check out Returns & Warranty before contacting support.

[MintyFox]

So fitbit support told me to deregister the device then register it again. After doing so the heart rate now does not jump up if I shake my wrist, I tried immobilizing my wrist and then running in place and it counted my heart rate until it got to 110, then it lost connection, gave me a "- -" then reconnected a little later with 130 which was accurate.

So its definitely functioning differently now, certainly more accurate, only thing that bothers me is that it cuts out while the heart rate is rising. Is that normal?