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.

[Babinator]

I was a runner and wondered why how the algorithm distinguish sleeping heart rate from resting heart rate etc, I’ve seen some great opinions from users.

Sent from my iPhone

[Kagakusha]

it presumably uses the accelerometer to detect patterns of slight movement typical of sleep. One could ask the same question if it’s sleep quality monitor.
But the traditional measure of ‘resting heart rate’ does NOT include data whilst asleep.

[CrystalClearly]

You are very generous in saying there might be "some meaning to watching long term trends in resting heart rate...." Since they hide their algorithm, we have no reason to believe that it is the same algorithm over time.

Traditional measure or not, Fitbit's algorithm for resting heart rate must include time when asleep. There is always a resting HR listed when I wake in the morning, and I have certainly been asleep since the previous midnight.

Moderator edit: merged reply

[dlhnj]

This was actually my original question to Fitbit - has the algorithm been modified over time?  I am not so concerned how they calculate resting heart rate but would like to know if they are changing how they determine it.  I have been monitoring my resting heart rate for the past 4 years.  It has remained fairly constant - range is only +/- 3 beats per minute when looking at a monthly average.  So I don't think they have changed the algorithm over this time. 

[Kagakusha]

Well of course it includes overnight heart rate.
They explicitly say so.
It’s that that makes their measure of ‘resting heart rate’ essentially meaningless for comparison to anything else.

From my iPhone - please excuse spelling checker induced nonsense!

I don’t think anybody except Fitbit knows.
The refusal to provide the algorithm, and the use one no one else uses, severely limits its utility.

My *impression* is there has been no obvious change over the last two or three years.

Harvey

Moderator edit: personal info removed

[Oregonmama]

That is what it should do, but clearly not what it actually does. Comparing my step count graph to my heart rate graph says it must be calculating my RHR when I am walking.

[Manupuri42]

I wear my charge 3 to sleep every night. My average sleeping heart rate is 62 - 65 as per detailed sleeping heart rate graph in Fitbit premium. But my average RHR doesnt go below 70. Why ?

[Kagakusha]

It’s perfectly normal for your overnight heart rate to be significantly lower than your ‘resting heart rate’ RHR.

RHR is normally defined as your heart rate at rest *whilst awake*; heart rate whilst asleep has NO role in the usual definition.
Fitbit refuses to reveal how it calculates RHR, but as it clearly says it DOES use heart rate whilst asleep, the result cannot be compared to anything else.

In fact the normal definition of RHR is poor.
It doesn’t define how long you have rested for, whether you have used alcohol or nicotine etc, whether you did really heavy exercise earlier in the day etc etc.

The Fitbit value can be of some value in tracking long term trends. Ignore short term fluctuations, and don’t compare it to anything else.

From my iPhone - please excuse spelling checker induced nonsense!

Moderator edit: personal info removed

[Babinator]

Thx

Sent from my iPhone

[Manupuri42]

Thanks a lot professor.

I agree. I also had something similar in mind.

👍

[Oregonmama]

Even long term trends don’t mean much, if your exercise habits change.

[Kagakusha]

Yes, long term trends can have some significance, even if your exercise habits change.
If you stop exercising, your RHR will probably slowly rise as your cardio vascular fitness slowly reduces.
Conversely a harder regime may make it fall as CV fitness improves.
RHR is one crude indication (and only a rough indication) of CV fitness.

Just don’t look at day to day, even week to week changes, they get affected by all sorts of things. A mild cold raises my RHR noticeably for a few days; a good dinner out with a few glasses of wine and it will spike for one day. These say nothing about overall CV fitness.
But a reduction, retained over quite a period, probably does. Do some statistic if you know how.

Just don’t get hooked on worrying about it!

[Oregonmama]

What I'm seeing is that it rises/drops a lot based on how much time I spend
being active each day and what the pattern of activity is. If I sit all
day, except for a single exercise session, it drops dramatically. It may
slowly rise after that, but it would take a very long time being sedentary
most of the day to make up for the impact of the way this value is
calculated.
My real RHR has fallen and risen significantly in the months since I had
the Fitbit. (I'm hyperthyroid and found myself needing an adjustment to my
meds.) Neither shift in my real RHR was seen in my Fitbit RHR, because my
Fitbit RHR was completely swamped by other factors However, when I
manually looked at the daily graphs and estimated the numbers either for my
low HR each day or my HR at a time of day when I am usually resting, both
had a very clear signal. The alogrithm Fitbit is using for RHR pulls way
too much noise into the calculation for it to say anything meaningful about
RHR.
Fitbbit continues to claim that this number tells you something significant
about your health in the same was as the conventional HR. In reality, their
algorithm is so dominated by other factors, that it can't tell you that.
And yes, I know how to do statistics. I also know how to do error analysis.
The signal to noise ratio is way too low for the RHR to be meaningful,
especially since it isn't even consistent for a given person.
Of course, Fitbit can continue to wave their hands and do their dog and
pony show saying their RHR tells you the same thing as the one studied by
Dr.s because most people don't have a signal of any significance happen. I
just happened to be "lucky" in that way.

[Kagakusha]

Whilst I agree with some of what you say, the fundamental problem is really not just Fitbit.

I’m no fan of the Fitbit approach, which hides what it really measures and is not comparable to any other measure. But at least it will be consistent.

The whole concept of RHR is flawed, because there is no proper definition of what it is - in this respect conventional “Dr’s” RHR is no better than Fitbit.
It does not define how long after exercise; how long after ‘heavy’ exercise (I entirely agree there is a fast recovery then a much slower one), how long after a meal (digestion raises it) ; what time of day (diurnal rhythms affect it); alchohol, nicotine, etc etc etc. Then things like stress come into it.

So whilst the Fitbit RHR is seriously flawed, it has that one merit of consistency. Conventional “Dr’s” RHR is very little better.

Fitbit RHR or conventional RHR *measured in a consistent way* probably give a rough indication of CV fitness when compared over long timescales, say a month or more.

But getting obsessed about it will be counter productive; it’s a very crude rough and ready guide, where small changes should be ignored.

Harvey

[Oregonmama]

I understand what you are saying, but 10 bpm or so because you change when
you exercise isn’t a small change.

[Kagakusha]

Agreed, it isn't; as I've repeatedly said, RHR be it Fitbit or any other version is a very flawed measurement.
Unless you impose your own protocols to make it consistent, it's of very limited value.
Not quite *no* value; with care, & a good understanding of its limitations, some.

[Du92979]

This has been my experience too.  It never changes even if it is super low during the day it just stays with what I wake up with. 

[Kagakusha]

It’s odd in that respect. 99% of the time yes, it calculates a value shortly after you wake and sticks with that, whatever happens. I *assume* - but we don’t know - that it uses data from the previous day.
But I am absolutely certain that very occasionally I’ve seen the RHR change later in the day. But I have never figured out what causes this.

Fitbit should stop this silly guessing game by publishing the algorithm; the claim that it is commercially confidential is risible. The fact that they do not publish it will probably make this my last Fitbit device; so the secrecy is commercially damaging.

[warfest]

I find it very frustrating too when I see my heart beats at 49 while I am working at my desk (I am an endurance runner this is why it is low) and it says my resting hearth beats are at 61 when any other devices says it is lower. I dont wear my watch when I sleep... and I train several times a day but when I am resting, it is never at 60. It seems like it picks a random number every time.

[TinaMarie73]

I’m really not sure how it works to be honest. Sometimes my heart rate will be in the 40s and 50s when sitting and I do walk a lot but I’m not a athlete. Then it will get low at night. I just wonder if this is really accurate. It scares me because they say normal heart rate is 60 to 100. I’m clueless. I just hope for everyone everything is ok.