Your fitness tracker isn't exactly lying about your sleep, but a lab test of 11 devices found accuracy varied widely, especially on sleep stages, so treat that 72 sleep score as a rough guide. Use the trend, ignore the drama.
Pick a short workout and read on.
This isn't medical advice, and a tracker can't diagnose anything. If you're worried about your sleep, talk to your doctor.
What the study did
A 2023 study in JMIR mHealth and uHealth compared 11 consumer sleep trackers against polysomnography (the gold-standard overnight lab test) in 75 participants at two sites in Korea. The devices included wearables (such as Apple Watch 8, Fitbit Sense 2, Galaxy Watch 5, Google Pixel Watch and Oura Ring 3), under-mattress or bedside devices and phone apps.
What it found
- Accuracy varied substantially between devices, so you can't treat "sleep trackers" as one thing
- Sleep stage agreement ranged from slight to moderate. Several devices showed moderate agreement with the lab test, others only slight
- Wearables tended to overestimate sleep, because they can miss short periods of being awake
- Limitations: modest sample sizes per device, participants from one country and the paper discloses that some authors have ties to one of the app's developers
What that means for you
- Totals and trends are more useful than stages. "I slept about the same as last week" is more reliable than "I got 47 minutes of deep sleep"
- Don't judge your day on one number. If you feel fine but the score is low, the score isn't the boss
- Beware of tracker anxiety. Worrying about sleep can make sleep worse. If the number stresses you out, take the watch off for a few weeks
- Pay attention to how you feel. Energy, mood and appetite say a lot. Read no motivation to work out
What trackers are good for
- Spotting a pattern (bedtime drifting later, say)
- Seeing the effect of late caffeine or alcohol on your own nights. Read coffee before training: performance boost or sleep tax and does one beer ruin your workout
- Keeping a consistent routine. Read make working out a habit
- Counting steps. Read how many calories does walking burn
What they're not good for
- Diagnosing sleep disorders
- Settling arguments about sleep quality
- Telling you exactly how much recovery you need
Use it alongside better measures
You can track progress without a wrist device. Read track fitness progress without a scale and scale not moving, clothes fitting better. And if sleep is your actual problem, read bad sleep and belly fat.
FAQs
Which tracker is the most accurate?
The study found large differences, but it's a single study and devices change. This post doesn't recommend a brand.
Should I stop wearing mine?
Only if it makes you anxious. Otherwise use it for trends.
When should I see a doctor?
If you snore heavily, stop breathing at night, feel exhausted despite enough hours or have other concerns, ask your doctor.
The bottom line
Your tracker is a rough diary, not a judge. Pick a short workout and trust how you feel along with the data.
Go train, FATBOY.
Sources
This article is general information, not medical advice, and the research it describes is limited and often small. Train at your own risk. If you have a health condition, take medication or are unsure whether exercise, caffeine, alcohol or a diet change is right for you, talk to your doctor first.
- sleep
- fitness trackers
- wearables