![]() It’s true that Fitbit’s sleep staging is only correct in these 30 second blocks slightly more than two thirds of the time and, moreover, this fact is not communicated to users in the Fitbit app. If you’re thinking this accuracy is low, well, that depends on the context. That’s where Fitbit comes in: the watch’s sensors can classify sleep stages with 69 percent accuracy in any given 30 second time window, according to a paper published by Fitbit scientists in 2017. But most of us don’t have polysomnogram equipment at home, or a physician to read it. How do doctors and scientists determine what stage of sleep a person is in? This is done using a technique called polysomnography, which uses many bodily sensors, including EEG, to determine if a person is in N1, N2, N3, REM, or awake. The first two stages, N1 and N2, are considered light sleep, and N3 is considered deep sleep. There is only one stage of REM sleep, but multiple stages of NREM. Because vivid consciousness occurs during REM sleep, the EEG recorded during this sleep stage basically just looks like the EEG of a person who’s awake. If we record electrical brain activity while a person sleeps using a technique called EEG, we see that brain waves become slower and larger in amplitude, a hallmark of internal brain synchronization, as the person progresses into deeper and deeper sleep. This pattern then reverses itself until a person eventually either wakes up or enters REM sleep. As you fall asleep, your brain becomes more internally synchronized, allowing less information to be processed. Although researchers have learned that volunteers in sleep labs do recall having some sort of conscious experience most of the time when awakened from NREM sleep, the quality of these experiences seem to differ from the vivid dreams of REM sleep. Sleep can be broadly divided into rapid eye movement (REM) sleep, when a person is most likely to be dreaming, and non-REM (NREM) sleep, when a person is more likely to be in a dreamless sleep. Next, we need to understand the different stages of sleep. The Fitbit Versa also features an SpO2 sensor for measuring blood oxygenation, but Fitbit is not yet using this feature to tell you about your sleep (more on this later). PPG measures blood flow based on how green light from an LED on the back of the watch is reflected by the body.īasically, Fitbit looks at how much you’re moving and how often your heart is beating to infer whether you’re awake, in a deep sleep, a light slumber, or dreaming. To learn about how Fitbit can monitor my sleep, I tracked my nightly slumbering with a Fitbit Versa watch for two months. (Full disclosure: I received this product free of charge from Fitbit to review.)įirst, how does a Fitbit watch monitor sleep? The Fitbit Versa infers when you’re sleeping and what stage of sleep you’re in using an accelerometer (an instrument for measuring bodily accelerations of the wrist) coupled with a technique called optical photoplethysmography, or PPG. ![]() As I’ve discussed in previous posts, sleep is essential for draining the brain of toxins linked to Alzheimer’s disease and for consolidating memories from the previous day. Getting a sufficient quantity and quality of sleep is not only a core component of health, but often an underappreciated one. ![]() But one of the smart watch’s most useful features is arguably what it monitors while you’re burning the fewest calories: your sleep. ![]() When you hear the word “Fitbit,” you probably think about logging steps, calories, and cardio. If someone had told me a year ago that he sleeps with his watch on at night, I’d probably wonder just how eccentric of a personality I was dealing with.
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