What do these wearables measure? How accurate are these measurements? How do they differ from medical sleep studies? Importantly, how should the information collected be used to make changes to improve sleep and reduce insomnia? Let’s consider these important questions and discover how to use fitness trackers to sleep better.
Sleep Metrics
There are many wearable devices available that can be used to track fitness goals and even sleep. Some of the most popular options include the FitBit and the Apple Watch. There are also smartphone apps, smart beds, mattress pads, and stand-alone products that can track sleep metrics. What kind of information is collected?
Movement
Most devices are tracking movement and are variations of actigraphy, measuring movement velocity and direction with an accelerometer. It may be assumed that stillness equates with sleep, and movement corresponds with activity and wakefulness.
Biometrics
Sophisticated devices may detect body temperature, heart rate, or energy expenditure. It may even be possible to measure electrical current conductivity within the skin. Sound may also be detected, sometimes via vibration, that may correspond with snoring.
Schedule
Timing is important to sleep quality. Sleep trackers may prompt you to provide guideposts. For example, it may be possible to input information about your bedtime, wake time, and even naps to help track sleep patterns over an extended period. This information is often collected via a sleep log and may help to identify a circadian rhythm disorder which occurs if a persons internal clock is misaligned. The degree of desynchronization is largely dependent on an individual’s genetics and the extent to which day and nighttime patterns are interrupted.
Environmental Characteristics
Some devices may also be able to identify other environmental characteristics, such as lighting, temperature, and noise. These may be useful to support the other variables that are measured. If the room is dark, it is nighttime, and if it is quiet, it is more likely that he or she would be asleep.
Accuracy
It is natural to wonder how accurate sleep trackers are in measuring the characteristics of sleep. If you were dieting and using a scale, you would certainly want to ensure the weight that it was reporting was close to reality, both true to the actual value (accuracy) and repeatable over time (precision).
Sleep is more than just lying still. Someone could lie perfectly still and a wearable may believe this inactivity corresponds to sleep. Similarly, movements may occur during sleep that do not necessarily correspond with complete wakefulness. Many “awakenings” detected by a device will go unnoticed by an individual.
It is possible that other measurements may help to strengthen the accuracy of these observations. Breathing and heart rate become very regular in deep, slow-wave sleep. This may help to indicate a person has fallen asleep, as this stage of sleep occurs early in the night. Heart rate patterns, oxygen levels, and other biometric measurements may help improve accuracy.
Unfortunately, many sleep trackers are products that are designed for consumers without scientific validation. The measurements may not be either accurate or reproducible. Artifact (such as movement of a bed partner) may interfere with the measurements. Moreover, the collected information may not correspond to the gold standard measurements.
Wearables vs. Sleep Studies
When sleep is measured by a diagnostic polysomnogram in a sleep center, there are a number of important characteristics measured by numerous sensors. Imagine all the information that can be collected.
These measurements include the brain wave activity as measured by electroencephalogram (EEG), muscle tone, the movement of eyes, other body movements, oxygen levels, heart rate, and sometimes additional data (such as carbon dioxide levels). No fitness trackers are able to collect all of these data. The nightly sleep patterns the wearables provide—showing light, deep, and even REM sleep—are not as accurate as the information gathered with formal sleep testing. They never could be.
In fact, sleep trackers are perhaps closest to a simple actigraph, a small wristwatch-like device that measures movement to give a rough pattern of sleep and wakefulness. These data can be very difficult to interpret, even by expert researchers, and the messy signals may be inscrutable to an algorithm.
What is a person to do? How can you use the data that is collected via a wearable sleep tracker to optimize your sleep?
How to Use Wearable Data
Though the data collected by wearables or other sleep trackers may be imperfect, it can still be useful. It may be important to take a bird’s eye view of the information that is collected. Consider these simple recommendations:
Trust Your Own Experiences
Before buying into the data collected by an imprecise—and possibly wholly inaccurate—device, reflect on your own sense of how you are sleeping. Do you recall waking 30 times in the night? Do you remember dreaming, even though the device reported no dream sleep? Are you having difficulty explaining the sleep pattern it provides? If you feel like you are sleeping well, consider simply ignoring the sleep data your device may provide.
Use the Information to Reinforce Good Sleep Habits
Healthy and constent sleep habits can help you to improve the quality of your sleep. It is helpful to keep a regular sleep-wake schedule by getting up at the same time every day, including weekends. Go to bed at about the same time every day. Go to bed when you are feeling sleepy. Try to get at least 7 to 9 hours of sleep nightly, meeting your own sleep needs. Avoid naps when possible. If the sleep tracker helps to reinforce a regular schedule, it may be useful.
Don’t Sweat the Details
There is evidence that data collected by sleep trackers can stress people out (a concept inelegantly called orthosomnia). It can add to anxiety and make insomnia worse. People become obsessed with the details, trying to explain every little blip in the data. If you find this is leading to obsessive behaviors for you, this could be a problem. Let it go. It may not be accurate anyway.
Corroborate the Data With Witness Testimony
There may be some inexplicable findings from your sleep tracker data. Perhaps some unremembered steps accumulated in the night. There may be frequent awakenings or restless sleep. The device may even report loud snoring. Try to verify these reports by asking a witness: consider questioning a bed partner. Learn if you sleepwalk, restlessly toss in the night, or rattle the windows with snoring. If there is a discrepancy, consider gathering more information before jumping to any conclusions based on the wearable’s assessment.
A Word From Verywell
It is fun to learn about ourselves. Sleep can be mysterious. Most of the night goes unremembered. It is natural to want to lift the curtain and glimpse a little about what occurs once our eyes close and we fall asleep. Be careful about putting too much faith into the accuracy of sleep trackers. The technology may improve with time, but these devices may be more novelties than serious scientific analyses. If you are struggling to sleep, get help from an expert.
