Monitoring Sleep with an Activity Tracker: Things to Consider


In recent years, fitness trackers have exploded in popularity. Along with tracking activity, many devices also allow the user to track sleep. Other devices may be made specifically for tracking sleep. It makes sense that Americans are more interested than ever in learning about their sleep habits and how to improve them. The National Sleep Foundation reports that 45% of Americans say that poor or insufficient sleep affected their daily activities at least once in the past seven days. Professional sports teams are also starting to encourage players to wear sleep trackers in hopes of getting a more clear picture of how a player’s sleep habits can affect his performance on the field. 

Unfortunately, there isn’t a lot of data to back up many of the claims surrounding the benefits of using these devices to track sleep. As we examine below, there are both pros and cons to sleep tracking.

How Wearables Track Sleep

Most wearable sleep trackers use a motion tracking sensor called an accelerometer. These devices use the info collected from the accelerometer to estimate time spent sleeping and time spent awake. As far as the tracker is concerned, sedentary= sleep and moving=awake. As you may be thinking right now, this isn’t necessarily always true, and is proving to be one of the fundamental issues concerning the accuracy of these devices.

Sleep Quantity Vs. Quality

In order to get a clear picture of our sleep pattern, we need to look at both sleep quantity and sleep quality. Professional sleep labs use sophisticated metabolic chambers to monitor things like heart rate and respiration, which can provide detailed information regarding sleep quality.

Currently, most wearable sleep trackers have no method of measuring sleep quality (e.g. hours of sleep spent in Rapid Eye Movement). Rapid Eye Movement (REM) sleep is the second stage of sleep that is much deeper than the initial stage. It is in the REM stage of sleep that we dream, store memories, and recharge so that we are better able to concentrate, learn, and pay attention during our waking hours. During this stage of sleep, heart rate slows and a number of other actions occur within our bodies. Unfortunately, sleep trackers are unable to discern the different between REM sleep and non-REM sleep in the same way that a metabolic sleep chamber can.

Accuracy and Behavior Change

The results of one study published in the International Journal of Behavioral Nutrition and Physical Activity showed that activity trackers were “quite accurate” at tracking sleep quantity. Conversely, most research on the accuracy of wearable sleep tracking technology shows that total sleep time is usually over-reported and wakeful time is underreported. This becomes an issue when the amount of waking time is masked by the tracker, but the person may actually have a clinical sleeping disorder. This is why sleep specialists recommend you seek medical advice if you have any doubt about your sleep quantity or quality.

Regardless of accuracy, wearing a sleep tracker can be an eye opener, especially for those who are unaware of how much (or how little) they are sleeping. Simply being more aware and paying attention to your sleep habits may also help you to make a behavior change, such as going to bed earlier. If you simply want a rough estimate of your sleep quantity, a tracker may do the job. But, if you’re concerned that you may have insomnia or a sleep disorder, such as sleep apnea, it is best to seek professional advice.

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