If you own a fitness device with a sleep monitor, chances are you’ve checked just how many ZZZs you’re catching. And why not? Data on how our bodies operate is fascinating. But, if you’re using the insights for anything more than fun, you should be aware of what these devices can—and cannot—tell you.
Most sleep trackers use an accelerometer (a motion-sensing technology) to determine if you’re asleep. More advanced versions also use heart rate variability. Both of these measures tell you approximately how much sleep you’re getting. However beware, different devices either overestimate or underestimate this number. Hours of sleep, sleep stages, and how well you’ve slept are just guesses.
Instead of looking at the specific numbers, it’s more valuable to look at your overall trend. Is the sleep tracker telling you that you’re getting insufficient sleep on a daily basis? Are the times that you go to bed and wake up inconsistent, which can lead to problems like sleep onset insomnia? Paying closer attention to your patterns and making sleep a priority can help you develop healthier sleep habits.
A sleep tracker can also help you understand what normal sleep is for you and set a baseline that may allow you to pick up on sleep issues. However, don’t count on it to indicate more complex concerns, such as sleep apnea, as these devices aren’t that sophisticated yet. Additionally, because people wear fitness trackers on their wrists, these devices can’t screen for a lot of sleep disorders, since not all sleep issues are associated with extra arm movement.
To truly assess your sleep, you need to undergo a sleep study. Sleep studies look at a lot more than arm movement and heart rate. They also measure brain waves, air flow from the nose and mouth, chest and abdominal movements, and leg movements. These extra features tell doctors exactly how much sleep a person is getting at night and how often they are waking up, and may point to breathing or movement disorders.
If you are noticing problems with your sleep, waking up a lot, or getting up in the morning without feeling rested, talk to your doctor—no matter what your sleep tracker is saying. Sleep is essential to our well-being, and a physician can help you find a way to get the rest you need.
Dr. Andrew Hong is a sleep medicine physician at Vancouver Clinic’s Columbia Tech Center location. He treats both adult and pediatric patients with various sleep disorders, including sleep apnea, narcolepsy, insomnia, parasomnias, and restless leg syndrome.