A friend of mine recently received a fitness tracker for her birthday. She was immediately inspired to get out and move more to meet her daily 10,000 step challenge. However, an unintended consequence of wearing the new device was her discovery that, apparently, she didn’t sleep very well. My friend has a high-stress job and a lot going on in her personal life, so she was aware of feeling fatigued before she got the fitness tracker. Now she had confirmation that her exhaustion wasn’t just her imagination. She wasn’t getting good sleep. But was the information from her tracker accurate?
Polysomnography, or a sleep study, is considered the gold standard for diagnosing sleep disorders. It records not only brain waves to determine your sleep patterns, but also your blood oxygen level, heart rate, breathing, and movements while you sleep. Measurements are taken using various sensors attached to your head and body.
Actigraphy, which has been around for more than 25 years, is another form of monitoring. Actigraphs are usually worn on your wrist and measure movement using an accelerometer, the same device used in most fitness trackers. Unlike polysomnography, which focuses only on what’s happening while you’re asleep, actigraphy measures your total activity, providing such metrics as total sleep time, whether you wake up after you’ve gone to sleep, circadian rhythms, and daytime inactivity. The advantage of actigraphy over polysomnography is it can monitor a subject over a period of days or weeks, providing a more comprehensive picture. It’s also much less cumbersome and disruptive than polysomnography.
The disadvantage to actigraphy is it’s prone to misinterpret data. For example, if you are awake but not moving, an actigraph may record this time as sleep. Conversely, if you’re asleep, but restless, the actigraph may record that time as awake.
According to the Australia-based Sleep Health Foundation, using a monitor to track sleep probably isn’t going to be a problem for most people and may even be helpful. For example, if you regularly go to bed late and wake up feeling groggy, a sleep monitor can help you identify your patterns so you can make adjustments and improve your sleep time and quality.
But if you have a sleep disorder, the device could give you false reassurance about your sleep habits. You may have sleep apnea, for example, but if you don’t move much even though you aren’t breathing properly, the device isn’t likely to let you know there is a problem. Alternatively, the device could create anxiety about not getting enough sleep. Research has shown that anxiety around quality of sleep can actually worsen the problem.
As wearables are increasingly being used to assess sleep quality, researchers have begun to study their accuracy. The results have been mixed. Nevertheless, it’s a big draw for some people who are considering buying a wearable.
If you’re considering buying a wearable for sleep, these are some of the more popular devices for you to consider.
The Basis Peak ($199) was the first fitness tracker to incorporate more sophisticated instrumentation and measurements in an effort to provide more comprehensive insights to how you’re sleeping.
The Peak uses a combination of an optical heart rate monitor, an accelerometer, and sensors that measure your skin temperature and galvanic skin response (changes in your skin’s electrical charge) to automatically track sleep duration, REM (rapid eye movement — the dreaming phase) sleep, deep sleep, number of interruptions, and how much you toss and turn during the night. The data is fed into the Basis Advanced Sleep Analysis algorithm, which provides a daily sleep score to help you evaluate your sleep quality; sleep trending, a rolling average of sleep patterns over time; and a weekly sleep report, delivered in an email that charts your sleep progress for the week. Information is presented in the associated app, which you can download to both iOS and Android phones.
The company has taken the extra step of validating the technology, teaming up with sleep researchers from the Stress and Health Research Program, a joint venture between the University of California, San Francisco, the San Francisco Veterans Affairs Medical Center, and the Northern California Institute of Research and Education. The company notes that “none of the institutions were compensated in any form for these studies.”
During the study, sleep duration and sleep staging were measured by both the Basis band and polysomnography. Data captured were compared, and preliminary results show a good correlation. According to the Basis website, additional research is ongoing.
The website also notes: “Sleep detection is based on a combination of heart rate and actigraphy. Activities, such as watching TV or reading, where your heart rate is low and your body is still may be considered a sleep event. We are constantly working on improving our sleep detection so that these false positive sleep events will not occur.” Unfortunately, if one of these events does occur, there isn’t a way to go into the app and edit the information.
The latest offering from Jawbone, the UP3 ($179), also automatically tracks deep, light, and REM sleep, the number of times you woke up, the total time you were awake, and how long it took you to fall asleep. In addition to the standard accelerometer, UP3 uses bioimpedance sensors to measure your heart rate, respiration rate, body temperature, and galvanic skin response.
The tracker syncs your sleep data with the UP app, which is available for both iOS and Android phones. Within the app, a detailed summary of your most recent sleep event is provided. You can also set a long-term sleep goal, and the app will tell you how close you are to achieving it. Unlike other trackers, none of the Jawbone products include a screen on the actual device. You must retrieve all recorded data from within the app.
If you think any of the data isn’t accurate, you can edit it within the app. You can also choose to track your sleep manually, which allows you to record naps and your sleep duration if you forget to wear your tracker to bed.
Although they don’t measure the different sleep stages, all of Fitbit’s wrist-based trackers automatically detect your sleep. The trackers ($100 – $250) rely on their accelerometers to measure movement, or lack of it, to indicate when you are sleeping. You have the option of recording sleep in either sensitive or normal mode. The normal setting counts significant movements (such as rolling over) as being awake and is recommended for most users. The sensitive setting causes your tracker to record nearly all movements as time spent awake. According to the company website, this setting may be helpful for users with sleep disorders.
The company also states: “If your Fitbit tracker is worn consistently each night with the same setting, the data that it produces should be useful.” The data is basically total time slept, and how much of that time you spent either restless or awake. So if you get up in the morning feeling less than refreshed, a glance at your sleep log may give you a clue as to why.
Because the devices detect sleep based on movement, it’s possible to have a sleep event recorded when you are awake but being still. If this happens, you have the option to edit the data in the app. You can also manually add or delete a sleep log. Fitbit automatically defaults to a sleep goal of 8 hours, but you can also edit this setting in the app.
Although the trackers automatically detect when you’re asleep (because you aren’t moving), when you wake up you have to sync the tracker with your smartphone to see the previous night’s sleep stats in the app. Fitbits are compatible with both iOS and Android phones. Most Fitbits also feature a silent alarm that vibrates when it’s time to wake up.
Misfit, Garmin, Moov, Polar, and most other activity trackers also monitor sleep. However, they primarily use actigraphy exclusively. Some are automatic, and some you need to switch to sleep mode before you go to bed. As we noted previously, sleep information based on movement alone is limited — you won’t know how much time you’ve spent in the different sleep stages. But if you’re just trying to get an overview of your sleep habits in context with the rest of your daily activities, this may be all the information you need. It probably isn’t necessary to have a device that tells you every detail about your sleep patterns. After all, if you’re having trouble sleeping, you probably already know it.
Bottom line: sleep trackers can provide you with useful information about your sleep habits in general, but they can only tell you so much. If you think you have a sleep disorder or if you’re having significant problems sleeping, talk to your doctor.
February 09, 2016