A lot of people with insomnia show me their FitBit results. Mostly it is to share some objective data that shows that their sleep is poor. Either short or broken up into many fragments or both.

Activity trackers can be very helpful when you have difficulties sleeping. A first question however becomes: How accurate are they?

There have been multiple studies comparing activity trackers with electroencephalography (EEG). EEG testing involves wearing leads on your head (similarly to when doing an EKG) to measure brain activity and gives you a highly accurate picture of how much you sleep and which sleep stage you are in. Researchers have had people wear an activity tracker as well as EEG leads and compared the results.

Activity trackers are very good in fact at estimating how much we sleep. They usually come in within 15-30 minutes of the total sleep time measured by EEG. However, they are not good at telling one sleep stage from another.

In other words, your fitbit is good at telling you how much you have slept but not necessarily at how much of a certain sleep stage you were in.

The second question I want to ask at this point is: How often does a healthy sleeper wake up per night?

There are no guidelines or criteria for but when it comes to complete awakenings that we are aware of most would probably say that not waking up at all or waking up once is normal. However, when part of your job is reading sleep studies you know that the picture is more complex.

Having an arousal (when your EEG shows an awake pattern for 15 seconds or less) is normal up to 15 times per hour! Having 6-8 EEG awakenings (EEG shows awake pattern for more than 15 seconds) during a night I would consider pretty typical. In fact if I read a sleep study and someone had less than 4 EEG awakenings during the night I would find that unusual.

Why am I bringing this up? I want you to know that when you look at sleep objectively, even healthy sleepers have a lot more active sleep than you would think. Why does this matter to you? Because your FitBit readings should not be stressing you out or causing insomnia.

Ask any physician and they will recognize the saying “treat the patient not the numbers”. If it comes to lab values, x-ray results or fitbit readings how the patient is doing trumps everything else. Let me elaborate by sharing some scenarios with you.

1. Let’s say you are having terrible insomnia and your sleep tracker shows that you are waking up frequently. The readings in this case do probably reflect your insomnia and when you sleep better you will see that your readings improve as well. However, if you start sleeping better but your tracker still shows erratic sleep then don’t worry. It is probably just picking up arousals and brief awakenings that most people are not aware of.

2. You are sleeping good but your sleep tracker is showing that you only have 3 hours of deep sleep and 4 hours of light sleep. Don’t worry. The tracker is probably correctly estimating your total sleep time to 7 hours. However activity trackers are not good at telling one sleep stage from another. If you feel rested then you are getting the amount and quality sleep you need.

3. You feel like you’ve only slept 4-5 hours but your sleep tracker is saying that you slept 7 hours. This could be because you are lying very still and the fitbit interprets this as sleep. You can try to increase accuracy by making sure that you move your arm at all times when awake. However you could also have some sleep state misperception and underestimate how much you sleep. If you find that even when you are moving at all times when awake the tracker still estimates you sleeping 2 hours more than you think then it is probably correct and you probably have paradoxical insomnia.

In summary I want to tell you that your sleep tracker is good at telling if you are awake or asleep but not very good at telling you how much deep or superficial sleep you’ve had and that even healthy sleepers do have several awakenings at night. How you sleep is very important. What your FitBit tells you about your sleep can be helpful, but not at all as important as how you feel.