Your Heart Rate Is the Key to Smarter Sleep Stages. Here’s Why.

heart rate during sleep stages: woman checks her Fitbit Alta HR tracker

If you’ve been using a Fitbit tracker to monitor your sleep, then you know how important movement is to signaling when you fall asleep, wake up, or stir. But in order to determine your sleep stages—how long you spend in light, deep, and Rapid Eye Movement (REM) sleep—movement alone is not enough.

During sleep studies, “most sleep stages are scored based on brain waves,” says Michael Grandner, MD, director of the Sleep and Health Research Program at the University of Arizona in Tucson and a Fitbit sleep consultant. “Except during REM sleep when doctors are also looking for eye movements and a lack of muscle activity.”

In other words, you can’t determine light or deep sleep based on movement alone. “You need another signal,” says Grandner. “You need something else that is going on in the body that differentiates REM from other stages of sleep.”

So what’s that second signal? Here’s a hint: It’s something many Fitbit trackers can already track—heart rate!

Heart Rate During Sleep Stages

You’ve probably heard that your heart rate slows when you fall asleep, but did you know that it doesn’t stay steady throughout the night? Research shows that heart rate variability—beat-to-beat changes in your heart rate—fluctuates as you transition between light, deep, and REM sleep.

Fitbit Alta HR, Fitbit Charge 2, and Fitbit Blaze continuously monitor your heart rate variability along with your heart rate. When you sync your tracker in the morning, your device will use the heart-rate-variability and movement data it gathered during the prior night to estimate your sleep cycles.  

The result? A way to differentiate between light, deep, and REM sleep that doesn’t require multiple sensors, cords, and an expensive stay in a sleep lab.

In addition to detecting your sleep stages, adding heart rate to the mix also allows your tracker to better pick up on restlessness and short periods of wakefulness that you may not even remember. “Every 70 to 90 minutes when you transition out of REM and back to stage 1, you hit a fragile point where you might have a brief awakening,” says Fitbit sleep consultant Allison Siebern, PhD, consulting assistant professor at The Stanford Center for Sleep Sciences and Medicine and director of Sleep Health Integrative Program at the Veterans Affairs Medical Center in Fayetteville, NC. “Some people may even have a prolonged awaking at that point.”

Fitbit Sleep Stages Today

If you notice more awake minutes in sleep stages than in your previous sleep data, don’t worry. Sleep stages combines the time you spend awake and restless into total awake minutes. Plus restless sleep isn’t necessarily a bad thingstudies show it’s common for adults to wake up briefly between 10 and 30 times per night.

Ready to get started? Check out How do I track my sleep and then see How Your Sleep Habits Stack Up.

63 Comments   Join the Conversation

63 CommentsLeave a comment

  • Would it be possible to see HEB during the daytime? I am interested in the practice of HeartMath and would like to see it graphed through my Charge 2.

  • So for someone with an HR irregularity such as Dysautonomia…. this isn’t going to work? With HR changing all of the time, how could Fitbit accurately figure out my sleep stage? The app has just been showing “No Stages.”

  • How much time should we be in deep sleep to get a good nights sleep? It seems I spend most of the night in light sleep.

  • is there a place on the sleep tracker to see my heart rate as it goes through the different stages of sleep and awake overnight?

  • I would like my old tracker back,, I do not care for the new graph. is there a way to get the old graph back?

  • Since the tracker changed to “sleep stages” it has been next to useless. Is it possible to revert to the old system?

  • For those of us who are old (71) we often do not sleep for as long a period as the young and naps are an essential part of our total sleep. It would be nice if you could eventually track naps by sleep stage and for smaller periods of time so we can see how we are doing.

    • I agree I don’t know what they did in the software change but my fitbit was tracking my sleep rem,deep and light sleep…even during a nap. then stopped. I exchanged it as I figured it was broken. Now this one started to show my sleep rem, deep & light stages and it went back to only showing restless, asleep, and wake. I am 68 & sometimes wake up in the night…My husband bought it for me to see my sleep stages. I am wondering if they changed the sleep program software.

      • You could try changing your personal settings on your program information to a lighter sleep setting? May help.

    • Agree. We are totally reliant on naps. Our marriage would not survive giving up naps. Some good data on naps would be very interesting.

  • My husband says I hold my breath for quite a long time and then choke and start breathing again which I know is probably sleep apnea. My dr says I’m not tired enough to be referred but would my sleep tracker show this problem too show my dr?

    • To diagnose a person with sleep apnea, they conduct a sleep study with multiple complicated monitors and instruments. It’d be pretty cool if the Fitbit could do that! But perhaps not realistic. Your doctor might want to see your Fitbit information, and will definitely be interested in what your husband has to say.

      Please please get tested for sleep apnea and if you have it, please follow treatment. It’s a horrible killer, and it takes years off people’s lives. I’ve known at least a few people who died young from it.

    • Did your dr ask what other symptoms presented (in addition to tiredness) when you discussed sleeping apnea with him? My husband was diagnosed and treated for sleep apnea. Through this I became familiar with several symptoms of this serious problem. Not all doctors have an awareness of the full range of how sleep apnea presents.

    • Please demand your doctor to order a sleep study. If you indeeed do have sleep apnea, it needs to be addressed.

    • SA eventually causes heart failure. You need to be referred to a pulmonologist and/or cardiologist to monitor this and or be tested to see if you need CPAP or BIPAP.
      I work with many patients with this as a long time CCRN.

    • If I were you I would change a doctor. I too, hold my breath while sleeping and didn’t understand why I was tired and felt like I didn’t sleep enough. Only a sleep test overnight at a hospital will tell you if you have sleep apnea and it looks like you have it. I don’t know how old you are but if you let it go for too long, it will rob your memory. I’ve had mine as long as I remember and now my memory is very bad for my age. If you are diagnosed for sleep apnea, the treatment will follow and it will stop you from holding your breath. Believe me you will have a happier sleeping. Don’t let it take years off your life as Liz said. Fitbit cannot help you breath normally, it can only track your sleep.

    • Ensure the air you breath at night is absolutely clean. Use a HEPA filter down to 0.2 microns and have it gently flow across your pillow. In addition, change your pillow case every day.

  • How do I get the new sleep graph consistently?

    Certain days are switched back to old sleep graph even though it’s a whole night long sleep.

    Is it still possible to recall yesterday sleep quality in new sleep graph even enthough the old graph has been displayed ?

  • I have Charge2 and don’t really think it gives as accurate time of sleep as the cheaper version my daughter has. By using the heart rate it says they wait 3 hrs to determine your sleep pattern, well that 3 hours is not included in the result and in my case I may wake up before that 3 hr period is complete. I know I’m a restless sleeper, but I can’t get any accurate account of my night when I know I was in bed at 10pm and may have taken a short time to fall asleep and that I was in some type of sleep mode for the next couple of hours but my results say I only want to sleep at 3 or 4 am. I have tried setting a sleep log when I go to bed turning it on when I retire and off when I wake. It did say how long I was on the log but the results did not match the time spent sleeping or show the early part of my sleep. I put it on the sensitive mode and for three days and for those 3 days It said I had almost 4 hours of sleep for that entire period. This was one of the reasons I bought the more expensive FitBit Charge2.

    • Carol, which model does your daughter have? Would be interested in finding out how it graphs sleeping patterns since i also think my Chsrge 2 isnt accurate either. Thanks!

    • I am a restless sleeper as well and was having a lot of trouble with the new sleep stages when I first started using them. Now I have learned how to manipulate the data so that it is more representative of my actual sleep patterns. When my charge 2 shows that I’ve slept several times for very short periods through the night, but I know that I have actually slept all night long, I delete the short naps after I take note of the last wake time shown. Then, I extend the first sleep time on my dashboard to include the entire period before the final wake time that’s shown on the last period of sleep. I hope this helps you.

    • I have just purchased the HR specifically for sleep monitoring. This is the 1st Tracker I have purchased. Mine doesn’t record the 1st couple of hours that I know that I am asleep. During the work week I am only recording a little over 3 hours per night. I’m glad you also commented on this flaw, I thought there was something seriously wrong with me.

  • I’m not really thrilled about the new graph, I want to see how many times I’m restless, that was the reason I bought my fitbit. Is there a way to switch back to the old one?

  • Hi I am wearing charge 2 , but why I am unable to view my sleep stage? I have check I am wearing lose or tight, but already a month still can’t view my sleep stage.

    • I thought u could only view the sleep pattern on ur iPhone app . I didn’t know it would be visible on the Fitbit Chg 2 also. I will ck this out online or call Fitbit .

    • May be you have a cardiac “arrythmia absoluta” preventing the tracker to analyse a stable heart rate and in consequence any further analyse of your sleep…

  • I have central sleep apena. Can Fitbit monitor my breathing and send me a buzz to partly wake me Up so that I breath again?

  • My heart rate does not work since I charged my Fitbit two nights ago. I have tried restarting it but just comes up with–

  • Hey! I travelled on Monday night and on Friday night and feel certain that I slept a little. My guy but shows nothing whatsoever. Do we hVe to be in a lying, supine position for it to track sleep? I was in a n semi reclined state. Huh ?

  • I have atrial fibrillation and although I get results I only get the simple graphs which are hard to follow, is there any way I can get better graphs as the simple ones are not very useful.

  • I LOVE the Sleep Stages, when it works!!! I have the Charge2, & it only pops up about once a week, just enough to give me hope, & then goes back to the old, reg cycle. It ALWAYS says; that it was not able to detect a regular heartbeat, which is contradictory of what is stated in the info above, our HR changes all night through the stages. My HR is on the lower side. I wear it the same way during the day( & night), & it picks up my HR then just fine. What do we need to do diff to get the Sleep Stages on a reg basis? It’s one of the main reasons that I traded up & got the Charge 2, & for the Water Resistance.

    • My Fitbit2 went back to “Sleep Pattern” about 2 weeks ago and no matter what I did it would not go back to “Sleep Stage”. Today I got the “Sleep Stage” back and I did not do anything differently. Don’t know what will happen tomorrow!

  • I agree with Mr. Milnover, why are none of these questions receiving a response? I’ve had my charge for 1 night now and didn’t get the stages. I figured it was because it was too loose, but now I’m just left feeling like this function doesn’t really work. Guess time will tell, cuz you’re not, ha ha.

  • I agree with Mr Milnover, why are these questions not being awnserd? I’ve had my charge for 1 night now and didn’t get the stages. I figured it was because it was too loose, now I am just left wondering if this feature doesn’t really work. Guess time will tell, cuz y’all aren’t, ha ha.

  • Yes Bob – I too have wondered why the questions are not being answered by the ‘expert’. Perhaps Danielle could answer this. I’m not really sure what their role is in all this.

  • I recently returned from a long haul flight from Australia to the USA. My Charge 2 recorded 6+ hours sleep on the flight which amazed me as I just seemed to doze but perhaps did better than I thought! But when back home that night I recorded nearly 11 hour of restlessness with no details. Just wondering as I felt I had a wonderful sleep that night! Any idea why this was not recorded normally? Fitbit on wrist as usual,battery low but not abnormally so. Thank you. Julie Reynolds

  • This is a neat feature. If you read the paper linked under “Research” above, you might notice that the metrics they use for light and deep sleep are pretty similar. So I wouldn’t worry too much if it looks like you’re not getting enough deep sleep. It could just be that the tracker is logging some of your deep sleep as light sleep. It can’t be perfect based only on heart rate, but the proxies that the tracker uses are based on solid data.

  • My Charge 2 was giving me perfect read outs of the complete 4 stages of sleep each day for the first few months I wore it. Then it started irregularly alternating between the 4 stage and only 3 stages. Whenever my wife wore it, the display showed 4 stages! Then it only showed three stages. After visits with my physician and cardiologist, it was discovered that I now have an occasional skipped beat originating in my atrium. I’m told to ignore it!

    So, it appears that the Fitbit transition between 4 stages of sleep and 3 stages was an indication of changed heart operation.

    I hope this information helps someone.

  • My wife and adult kids bought me a Charge 2 for my birthday in mid-Jan. After about three days of use, I decided my wife should have one as well.

    Anyway, we are 74 & 71. Device is tracking sleep well and is consistent. My wife goes to the gym 4 days per week. Yoga and weight training 2 days each.

    Motivated by the Fitbit, I have been doing about 2 miles per day up and down steep hills. Fitbit records about 24 flights of stairs at the end of the walk. Combined with my other activity, I am getting about 7 to 8 thousand steps. Certainly a lot more than sitting at my PC.

    My Fitbit records sleep pattern as expected. Suggest that anyone finding disappointing results, call their tech support. This device has incredible capabilities but is not trivial to learn.

  • I am 83 years old and have been a very healthy person all my life until 8/13 when I experienced a serious Lumbar injury that literally left the disc in multiple pieces and resulted in Sciatic Nerve pinching, and numbness/tingling to my toes in my left leg.
    I had two stints installed in 4/17 after a blood work-up disclosed a cardiac event that I was totally unaware of, and now see my Cardiologist every six months and I now feel like my old-self, and go about my life normally.
    My problem with sleep occurs during the night when I am awakened by rapid heartbeat that manifest itself in my left calf and foot along the sciatic nerve. I can literally tell myself, calm down, we are not involved in exercise, or work, and my heart will slow down to a normal heartbeat, and that experience may repeat itself during the night?
    I now have a Fitbit Watch and beginning to explore its use.

  • How do I reset fitbit so I get all sleep stages. My fitbit is in correct position and monitors heart rate well. Tried switching fone on/off have synched fitbit it’s fully charged but still only basic sleep. What else could I do? Would be great if anyone knows or make other suggestions. Thanks, Chris

  • I love the design of the sleep stages.

    But why don’t Fitbit use HRV, because error message of missing sleep stages is: no constistant hear rate!
    When you have cardiac arrhythmia, you don’t have accurate heart rate!

    And why do I have sleep stages until an Fitbit app update, after that non?

    Why did you change the algorithm for sleep stages?

    Restarts, new installation, reconnecting, other position on the hand didn’t help.

    Support can’t help, only standard answer.

    When this is fixed and customer have accurate sleep stages, then will Fitbit have the best tracker!!!

    I’m looking forward to the the best Fitbit Ionic!

  • me gustaria saber si este aparato puede ayudar a controlar las arritmias cardiacas nocturnas, o por lo menos a controlarlas.
    muchas gracias.

  • The sleep tracker is the coolest part of the Fitbit… If only it it was useful like actually tracking stages…..

  • I am new to using Fitbit. I have the Charge 2. All I can say is that I am in awe of the sleep tracker. I have chronic fatigue and although I do not have an official sleep disorder, I have been told I have disordered sleep. No matter how much I sleep I never feel rested. So to have a tool to see what’s going on is just awesome. Maybe I can now figure out some insights on my own.

  • sorry to perhaps go over old ground. I do have very broken and restless sleep and my Charge 2 rarely records any sleep data. However it clearly shows my recorded heart beat all night. i understood this was what provided the sleep data so why is this not happening? confused and a shade disappointed at this information not being available, apparently.

    • I am experiencing the same thing. Cannot find good position for band. Past teo weeks have beeen nothing but restless sleep with the excuse that it could not get a consistent heart rate reading. Perhaps it is my heart rqte or BPM which coincidendly went to to very low 50 BPMs at same time. Maybe this is issue. Goiong to visually recoed my sleep with a motion based camera to see if I can get additional info.

  • Does it matter what bpm to record for sleep, my sleep bpm has gone down to around 50bpm in the last few weeks and since then i havent had a sleep record.

    • I am experiencing the same thing. Cannot find good position for band. Past two weeks have been nothing but restless sleep with the excuse that it could not get a consistent heart rate reading. Perhaps it is my heart rate or BPM which coincidently went to to very low 50 BPMs at same time. Maybe this is issue. Going to visually record my sleep with a motion based camera to see if I can get additional info.

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