By Brandon Peters, MD
If you have purchased a fitness tracker, like millions of others, you may wonder how to use the wearable device to improve your sleep. These sleep trackers may provide some valuable insight into an important of health and well-being. They can also be completely useless. 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.
What Sleep Metrics Do Wearable Fitness Trackers Measure?
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 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. There are variations on actigraphy. This measures movement velocity and direction with an accelerometer. It may be assumed that stillness equates with sleep, and movement corresponds with activity.
Biometrics
Sophisticated devices may detect breathing patterns, heart rate, or oxygen levels. 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. It may also 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 sleep logs and may help to identify circadian rhythm disorders.
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 a person is not moving, it is more likely that they would be asleep.
How Accurate Are Sleep Trackers?
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 will go unnoticed by an individual as it can take more than 5 minutes of wakefulness before a memory is generated.
It is possible that other measurements may help to strengthen the accuracy of these observations. Breathing becomes very regular in deep, slow-wave sleep. This may indicate a person has fallen asleep. 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 may interfere with the measurements. Moreover, the collected information may not correspond to the gold standard measurements.
Comparing Information to Sleep Testing and Studies
When sleep is measured by a diagnostic polysomnogram in a sleep center, there are a number of important characteristics. These include the brain wave activity as measured by EEG, muscle tone, the movement of eyes, other body movements, and sometimes additional data. No fitness trackers are able to collect all of these data. The nightly sleep patterns they provide—showing light, deep, and even REM sleep—are not as accurate as the information gathered with formal sleep testing.
In fact, sleep trackers are perhaps closest to an 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 Data to Improve Sleep
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:
1. 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.
2. Use the information to reinforce good sleep habits.
It is helpful to keep a regular sleep-wake schedule. Get up at the same time every day, including weekends. Try to get 15 to 30 minutes of sunlight upon awakening. 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.
3. Don’t sweat the details.
There is evidence that data collected by sleep trackers can stress people out. 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.
4. 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.
5. If you are not sleeping well, get help.
Many people use sleep trackers because they are not sleeping well. They are hopeful that they may learn a little bit about why they are having difficulty sleeping. If the insomnia persists, this search can become desperate. Although some insight may be gleaned, more evaluation may be necessary. If you have poor sleep, especially if you have trouble sleeping through the night with frequent awakenings or experience daytime sleepiness, get evaluated by a board-certified sleep physician to sort out what might be contributing to your troubles.
Conclusion
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 positing 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.