Are Sleep Trackers Accurate Enough to Matter?
Dreams were the initial study of sleep.
The ancient Greeks and Romans considered dreams to be messages and omens from the gods, and the Egyptians associated sleep with the spiritual realm, where the soul could leave the body and wander, linking dreams to divine encounters.
Later on, philosophers began making more scientific observations about sleep. For example, Aristotle described sleep as a cooling process that allows the body to digest excess heat that builds up while we're awake.
Then, in the 1900s, tools were invented to study sleep and deepen our understanding of sleep's importance in our lives, which ultimately led me to spend several hundred bucks on a Garmin watch that delivers a nightly "sleep score" with the promise of optimizing my physiology.
The Science of Sleep Tracking
Polysomnography is the current gold standard for dissecting one's sleep.
It requires the combination of several tools to measure the brain waves that occur during various sleep stages, muscle activity, and eye movements.
However, this happens in a lab, which is incredibly inconvenient, and I can't imagine that being watched while asleep is very relaxing.
This makes devices like the Oura Ring, Whoop, and the Apple Watch appealing by offering convenient, at-home sleep monitoring that gives us day-to-day measurements of stress and recovery.
Does It Work?
I was highly skeptical about my watch's ability to determine what was happening in my brain while I slept. And rightly so, because the watch only makes an educated guess about one's various stages of sleep.
I'm not exactly sure what each specific device uses, but here are some of the measurements used to estimate sleep:
Heart Rate:
- More specifically, greater heart rate variability (HRV) implies the takeover of the parasympathetic (or the rest and digest) part of our nervous system.
Movement Tracking:
- Accelerometers in smart devices detect reduced motion, distinguishing REM and deep sleep from lighter sleep stages where tossing and turning are more common.
- REM sleep is characterized by the paralysis of most voluntary muscles, called atonia, which is believed to keep us from acting out the movements in our dreams.
Respiratory Rate and Oxygenation:
- Some devices monitor breathing patterns via changes in blood oxygen levels and variations in heart rate that occur with each breath.
- Our body temperature decreases as we descend into deeper stages of sleep.
- Many devices rely on user input, like setting a scheduled bedtime, to make smarter assessments about what's occurring at that moment.
Overall, research shows that these sleep trackers aren't super accurate compared to an in-depth sleep study, and only a bit better than using movement tracking alone.
Does It Matter?
Based on these results, the skeptic in me asks why I would endure this metal block on my wrist each night if the results aren't super precise.
Furthermore, I glance at my score each morning, excited to see how I crushed my sleep the previous night, and then go about my day without a second thought about upping the ante with a PR sleep score or laying low because I got a failing grade.
So, what's the point?
My answer is less about the actual score and more about performance motivation.
When my sleep is being graded, I'm more inclined to make conscious decisions to improve that score.
I reconsider that afternoon coffee, drink less booze, and I'm less inclined to binge-watch Netflix into the night, knowing that all these things will impact my sleep grade.
So, while consumer sleep trackers might lack the precision of clinical tools, they promote an awareness of sleep and its role in overall well-being. This awareness often encourages healthier behaviors—like setting regular bedtimes or reducing stress—which is the ultimate goal.
In a world where sleep is often undervalued, these tools offer a practical nudge toward better habits and, hopefully, better health.
Originally published as Movement #244
