If you need your sleep analyzed, doctors will usually order a polysomnography, which analyzes a person’s oxygen level, heart rate, breathing, eye movement, and leg movement while simultaneously running an electroencephalogram (EEG).
An EEG shows your brainwaves through different stages and cycles of sleep. A wearable smartwatch or fitness tracker on your wrist, however, is far from your brain.
The most popular wearables by Fitbit, Apple, Garmin, and Samsung collect a combination of the following measurements: heart rate and heart rate variability (HRV), movement, breaths per minute, and skin temperature. Devices that track sleep cycles use an algorithm to hypothesize your sleep cycles based on the data.
A 2017 study compared a polysomnography with the performance of a Fitbit Charge 2 in 35 adults. Researchers found the Fitbit device detected sleep onset with 96% accuracy but overshot time spent asleep by 9 minutes on average. In the study, the Fitbit detected light sleep with 81% accuracy, deep sleep with only 49% accuracy, and REM sleep with 74% accuracy.
A newer study published in April of 2022 compared the performance of Fitbit Alta HR to results of an EEG conducted simultaneously on 40 college athletes while sleeping. This study found FItBit data to satisfactorily track sleep onset, time spent asleep, and sleep cycles. Fitbit can be a useful tool for athletes’ sleep management.
While not 100% accurate, the Fitbit data had a strong correlation with polysomnography data.