What You Can’t Learn From A Sleep-Tracking App

What You Can’t Learn From A Sleep-Tracking App

We are in the age of the "quantified self," where consumer hunger for gadgets that track steps, stress levels, and sleep habits is on the rise. The market for wearable technology has grown by leaps and bounds since its humble beginnings in the pedometers of the 1980s, and is estimated to triple in value between now and 2019.

With the market surge comes a healthy dose of skepticism from critics who say that manufacturers overstate the accuracy of their devices. When it comes to something as important as sleep, it’s worth taking a second look.

As an aside, if you use any kind of app or wearable device to track your sleep, congratulations on prioritizing one of the most fundamental parts of your health. Many people are barely aware of how many hours of sleep they get per night, let alone how long they spend in a particular sleep stage.

Firstly, let’s look at the technology devices use to track your sleep relative to the way scientists would in a sleep laboratory. The gold standard for sleep monitoring in a clinical setting is polysomnography, where a series of electrodes track electrical activity in your brain and map patterns of activity to different stages of sleep. There are four stages of sleep, and though the role of each is far from fully understood, we know that spending enough time in non-rapid eye movement deep sleep and REM sleep is essential for normal functioning.

In lieu of electrodes, fitness trackers rely on accelerometers, or motion sensors. The basic premise is that the more you move, the more restless your sleep is, and the less likely it is that you were in a deep or REM stage (note that REM and deep sleep are not the same thing, but both are considered essential). This is where it gets hairy. Experts say that while trackers may be able to tell whether or not you’re asleep, how much you move is simply not a reliable indicator of what sleep stage you’re in. Moreover, studies of fitness trackers show that they tend to over or underestimate how much time you spend sleeping, depending on the model.

What use is a sleep tracker, then? While it may not be worth getting hung up on "detailed reports" that purport to show you exactly how much time you spent in REM sleep, roughly tracking how much you sleep over a long period of time can be a useful reality check. You can also get a sense of how your lifestyle habits, like drinking caffeine or alcohol before bed, affect how much you sleep. In short, "big" aggregate data that comes from tracking your sleep for a significant period can be helpful, as long as you remember to take the rest with a grain of salt. The best barometer of your sleep habits is old-fashioned and cheap: how alert and well-rested you feel on a regular basis.

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