How does Fitbit calculate Resting Heart Rate?

[BigHaole]

I'm finding this very frustrating to be sitting at my desk, and see my HR showing as 74, but my Resting HR being 80.  Clearly Fitbit is not using the conventional definition (from Wikipedia):

"The basal or resting heart rate (HRrest) is defined as the heart rate when a person is awake, in a neutrally temperate environment, and has not undergone any recent exertion or stimulation, such as stress or surprise."

This definition would lead me to expect my reported resting heart rate to be the low value reached in the early morning, or at least the low value I reach, during the day.  Instead, it's above both of these.  I would like to know how it is being calculated, so I can know if my Fitbit is reporting anything useful when this number goes up or down.  Over the recent new years holiday, I got more sleep and more exercise, with less stress, so I was expecting this to go down, but it has gone up and I do not understand why.

[shipo]

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@sgalant wrote:

Workouts help to lower the FitBit RHR during the same day as well, before some of my track workouts I sometimes sit at about 54 and after doing some sets and reps I am at about 52 or 51.

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I think it depends upon the type of workout.  If I do a relative short run, say under five miles, my next day's RHR, as calculated by Fitbit, is typically 41-42, however, on days when I do longer runs, say ten or more miles or a race, the next day my RHR can be as high as 45.

[Babinator]

Wow I remember Bjorn Borg the tennis star had that RHR.   

Moderator edit: personal info removed 

[kbmm]

My heart rate at night dips as low as 36, my RHR is between 44 and 47, though there have been days when it's been 41. When I had pneumonia it went up to 58 for a while. All perfectly normal for me. It depends on genetics, fitness and a number of other factors. My physicians have confirmed that that is in fact, fairly accurate (whenever I get my pulse/BP taken). As long as you're not passing out, feeling weak, are able to exercise and feeling energetic etc., there is nothing to worry about!

[shipo]

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@Babinator wrote:
Do you ever thinks it's too low?

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I'm not sure if you're responding to my post or not.

The following comments, in no particular order, kinda-sorta answer your question from my perspective:

• Yup, when one's heart rate is zero, it is definitely too low.  🙂
• From what I've read on the subject, assuming no AFIB (Atrial Fibrillaiton), bradycardia (aka. Athletic Heart Syndrom), is not a bad thing.
• I have been fairly active my whole life and have always had a relatively slow heart rate; back in my teens I could routinely get it down into the high 20s when in bed, I'm in my early 60s now and the lowest I typically see recorded on 5-minute average plot from my Fitbit is 33 (most recently just last night).
• When I was in high school I was a middle distance runner, I had a doctor try and put me in the hospital because my heart was beating along well under 40 while I was in his office.  He insisted I go to the hospital and even called an ambulance; I jumped off his table and literally ran out of the office.

[kocytean_za]

Hi guys. I've been reading this thread with interest since I came here to understand how Fitbit measures your resting heart rate, and what it defines as your resting heart rate.

The reason I'm curious is that I'd expect my heart rate to be much higher than Fitbit reports it as. My RHR as reported by my Charge 2 (which I've been wearing for more than two months and wear to sleep) is between 56 and 64bpm. This is very surprising to me, because it's the RHR of someone who is much fitter (read: athletic) than I am. I'm a geek who spends 80% of his day behind a computer, except for an hour or so of active, intense exercise. My RHR as reported by my Fitbit started at 70bpm (measured in June, almost willing to disregard it since there's not a lot of historical data at that point). It's since dramatically decline to where it is now.

I thought, great! I'm definitely getting fitter. But, why does my Fitbit report my RHR as around 58bpm, when my heart rate as I sit typing at this desk, not having exercised at all today, is 80bpm?

Looking at my heart rate graph, my heart rate when asleep is at around 55-60bpm, and my heart rate when stationary is around 70-80bpm. I have never checked my heart rate wearing my fitbit at rest and seen a heart rate of below 60bpm.

I understand that Fitbit is not a medical device per se, but it is sold as a fitness tracker. I and others here clearly have some concerns that it's not tracking our fitness progress accurately and might be reporting numbers potentially based on miscalculations.

[Colmcq]

So I just got a fit bit for my girlfriend and I gave it a go for a laugh.

It reckons my rhr is about 60 which is interesting because here I am as an ex high level athlete with three cups of coffee down me, tapping away on the keyboard after a cycle ride this morning with my heart rate bobbling about 42. To say the way fitbit works out rhr is wrong is an understatement. It's useless. 

[shipo]

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@Colmcq wrote:

So I just got a fit bit for my girlfriend and I gave it a go for a laugh.

It reckons my rhr is about 60 which is interesting because here I am as an ex high level athlete with three cups of coffee down me, tapping away on the keyboard after a cycle ride this morning with my heart rate bobbling about 42. To say the way fitbit works out rhr is wrong is an understatement. It's useless. 

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How long have you had the Fitbit?  It takes a few days of history before the RHR is fully calculated.

I've had a Fitbit for well over two years and have never noticed anything like what you're describing; can you post your daily heart rate plot from the Fitbit.com dashboard?  It should look something like this:

The above graph, when taken in context of the Fitbit RHR calculation works out to a RHR of about 42. 

[JJTrav]

I always just assumed that RHR is some calculation based on something like the following:

Day before heart rate while not doing any physical activity and then looking at your sleeping heart rate for the night you just slept + a small correction based on current day activity. I say the small correction because I have seen this number change a few beats during the day before, but it is very rare, so I'm thinking the present day is counting something, but very little.

This number can be massively influenced by alcohol for me. Fitbit is quick to log an increase from it the very next day, but then seems to take days to bring the RHR down again after my normal heart rate has resumed (usually half way through the day after drinking). This can make me suspicious that Fitbit might be looking at a period of more than 24 hours.

I'm not sure what the state secret is here. If people don't understand the logic, they won't respect it.

[jsherman]

I agree that the resting heart rate is BS and it's even more BS that they say this is solved as they've never told us how they calculate it so it's not solved. Every heart rate monitor I've had in the past has said you check your heart rate first thing in the morning for resting heart rate. When I wake up in the morning and look at my wrist I'm 55 to 59. However Fitbit has lately been calculating me anywhere from 61 to 64. I watch my resting heart rate go up in the middle of the day which makes no sense as it should be taken first thing in the morning. I have no faith in their calculation and if they won't tell us how they do it I have less faith and they cannot say the problem is solved as this chain is how do they calculate rhr

[shipo]

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@jsherman wrote:

I agree that the resting heart rate is BS and it's even more BS that they say this is solved as they've never told us how they calculate it so it's not solved. Every heart rate monitor I've had in the past has said you check your heart rate first thing in the morning for resting heart rate. When I wake up in the morning and look at my wrist I'm 55 to 59. However Fitbit has lately been calculating me anywhere from 61 to 64. I watch my resting heart rate go up in the middle of the day which makes no sense as it should be taken first thing in the morning. I have no faith in their calculation and if they won't tell us how they do it I have less faith and they cannot say the problem is solved as this chain is how do they calculate rhr

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Checking heart rate immediately after waking up is old school; that was done because there wasn't a better way of tracking 24x7; unfortunately this process results in an artificially low "resting" heart rate.   Similarly, the old school way your doctor would take your "resting" heart rate was to wait for you to sit for a few minutes and then take it in the office, a process which, depending upon what you were doing immediately prior to getting into the office, could result in a reading which was as high as the "immediately after waking" reading was low.

The cool thing about the Fitbit formula is it calculates a resting heart rate which is higher than the sleeping rate, but lower than a typical day-time rate.  In my case my sleeping heart rate is typically between 33 and 35 BPM, my heart rate sitting hear typing this is 56, while today's calculated Fitbit RHR is 42.  Sounds pretty accurate and non-BS to me.

[Colmcq]

I had it where it was middle of day and hr was ten beats lower than what it
thought rhr was

[shipo]

@Colmcq, I've never once seen what you describe; please post a full-day graph (like the one I posted above) for a day where your RHR is 10 BPM higher than what you manually calculate midday.

[jsherman]

how do you get that chart? I have a blaze and do not see the option unless it's for a workout

[Colmcq]

With pleasure

Attached screen grabs. This I sent to support.

You want a graph too. I'm getting that for you

FYI my resting hr should be 36-3

[kbmm]

I agree with you. I think it's pretty accurate. Mine during the day fluctuates between 50 and 60 or so, depending what I'm doing (with occasional blips into the high 40s and much higher - 100s when I'm exercising). At night it's between 38 and 48. Today my resting is 44. On sleepless nights, or when I've had a lot of caffeine, or am sick, my night-time rates can go up into the 50s and my resting rate with pneumonia went up to 56 one time last winter. It seems very accurate to me and a good indicator of when I'm sick or under the weather (it sometimes starts rising a little right before I get sick, which shows that my body is working a little harder). The fact that it calculates in 5-minute intervals makes it much more accurate it would be if taken once a day when you're "sitting," which is what doctors do (or what people can do when they decide to take their pulse).

[shipo]

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@jsherman wrote:

how do you get that chart? I have a blaze and do not see the option unless it's for a workout

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You should be able to get it from either the Fitbit.com dashboard, Daily view for Heart Rate, or from your phone by using the daily graph; here's what a daily graph looks like from an Android device looks like:

[shipo]

@Colmcq, how do you know your RHR should be "36-3" (whatever that means)?  A daily graph would be far more instructive.

[Colmcq]

36-39

Typing this out from phone

I've been ill recently so daily graphs only go down to low 50s but still
lower than what it recons is rhr Edit: i can't screen grab from this computer and I can't find the bit where it has the graphs.

I got that other screen grab from my phone ages ago. This is so confusing.

Fitbit seems to be confusing something like average daily ambient HR with resting HR. Resting HR is when you're totally at rest just after waking up. Its not some mangled averaging of daily heart rates. Its a minimal value.

@shipo 33 RHR? WTF you seem like an endurance athlete all right, at least according to that graph you posted

[shipo]

@Colmcq, ahhh 36-39, got it.

On the Fitbit.com dashboard, make sure your "Activities" tile is being displayed; on that tile, set it to heart rate mode and the time frequency to Daily (if you look at the image in message #84 you'll see the two ovals in the upper right corner showing the mode and the duration).  From my phone, all I do is touch the Heart rate icon and then touch the day in question and the graph shows up.

Yeah, I'm a distance runner, the quote you pulled from my old post was referencing a time back in the early 1970s when I went to the doctor due to a bad case of poison ivy and he tried to hospitalize me because of my heart rate (which, while slow, was probably elevated compared to my norm because of how severe the poison ivy was).  I tried explaining to him I was a middle distance runner on my high school's track team, but he didn't seem to get it.

[greysave]

I have to agree with the original post.  I have the same issue with my Charge 2.  I don't know what algorithms it uses, but I can see my resting heart rate as much as 6-8 points lower at times during the day than what the app shows my rate for the day.  Now obviously I do not know what my resting rate is at night, but if I can see it lower than what the tracker says my daily rate is many times during the day and the sleeping rate should in theory be low as well....Seem like the measurement is flawed....