Individuals most often recognize fitness trackers for tracking steps and miles or tracking how many calories they burned, but fitness trackers also help track sleep! Fitness trackers have built-in sensors that help with the tracking and accuracy of the input. This software uses complex algorithms to sort out data that may prove useful to users later on. So how exactly do fitness wearables track sleep, you ask?
Most wearables come equipped with a “Sleep Mode” feature, wherein the users of these devices activate them to let the device know they’re about to slumber. Usually, this data is collected and measured as information is collected and measured while an individual is asleep.
Some devices, on the other hand, make use of actigraphy. This software translates movements into periods of sleeping and waking. Actigraphy can be incredibly convenient for people that live with sleeping disorders or even sleep disruptions. Users can wear an actigraph device at home, and most of them look like watches just the same. Some of them are worn 24/7 to track how an individual gets sleepy during the day.
Actigraphy is generally accurate for tracking sleep that healthy adults get, who have more “normal” sleeping patterns but have a higher margin or error for anything else. Actigraphy devices can under or overestimate sleep. Since actigraph devices rely on movements to track sleep, it may still think you are asleep when you’re laid up in bed or resting even if you are awake. The less sleep you get, the less accurate actigraphy can track it. Wake time is an even less precise aspect that actigraphy gets right since periods of no movement will almost always register as sleeping. If your movements while awake are limited or still, this might register as sleep and can have more sleep time recorded. Lying in bed and trying to be able to sleep can also register as sleeping, even if the mind and body are fully awake.
Another thing that contributes to an actigraphy’s inaccuracy is user error. Users may sleep in positions that restrict arm movements and therefore keep the tracker stagnant and unable to record any useful data or be recording too much movement if your breathing interferes and registers as actual movement on the tracker. Users may not remember to set fitness trackers on sleep mode. Users may even forget to wear the devices at all.
Polysomnography or PSG is also used in labs and holds the “golden standard” title for definitively measuring sleep. Most studies using actigraphy and its accuracy are compared to PSG data. Where actigraphy is convenient and can be done from the comforts of your own home, PSG testing requires sleeping in a lab where the brain waves can be monitored by Electroencephalography or EEG tests, where electrodes on the scalp measure the brain waves. Despite its inconveniences, it proves to be more accurate than actigraphy.
Most fitness trackers only rely on movements to be able to track anything. Built-in fitness trackers on a phone count steps based on how the phone moves, so if you swing it back and forth, it will count your steps just like regular walking. Using fitness trackers that claim to tell you how long you spend in a particular sleep phase is probably a ploy or marketing strategy. Sleep researchers argue that to record sleep data accurately, brain waves and eye movements are essential to assess these phases. Many other different methods of analysis can be used for more accurate tracking of sleep. Some devices might even use more than one way to get a more precise reading.
The bottom line is that if you struggle with sleeping disorders, it may be your best bet to consult a professional about it and suggest what you can do to track or improve these sleeping habits. While there is no harm in wanting to use a fitness tracker to track your sleep, understand that they are more accurate and made for those that generally sleep well. PSG tests can also help if you don’t. Addressing different sleep phases such as deep sleep or Rapid Eye Movement (REM) sleep, there is yet to be ample proof or study that fitness wearables can accurately predict these phases with the technology present today.
