Fitness trackers and sleep trackers are all the rage, but how much information can you actually get from a device on your wrist?
Can you trust the information on your device to actually measure how much sleep you are getting each night and the quality of that sleep?
These devices usually come with some big claims, but how do these trackers actually record the information that is so critical to your sleep?
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Supposedly these devices work by monitoring your body movements as you sleep, while some also look at heart rate changes to estimate how much of your sleep was a ‘deep sleep’ and how much was ‘light’.
A sleep expert from the University of Oxford, Dr Matthew Reid, explains that despite the popularity of these devices, only a few studies have investigated the accuracy of sleep trackers.
One study, which compared sleep trackers to the use of proper polysomnography equipment usually used to treat sleep disorders, found that they were only accurate 78 per cent of the time when identifying sleep and wakefulness.
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That might not sound too bad, but that accuracy then dropped to just 38 per cent when estimating how long it took wearers of the device to fall asleep.
“Polysomnography tests are the most accurate because they track a person’s brain waves, heart rate, breathing, blood oxygen levels, and body and eye movements during sleep through electrodes attached to the skin and scalp,” Dr Reid explains.
“Analysing brain wave patterns is the only definitive way of knowing whether someone is awake or asleep, and to know what stage of sleep they are in.
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“But since sleep trackers are worn on the wrist, they make their estimates of nightly sleep by measuring body movement and sometimes heart rate data.
“As we move frequently during all stages of sleep, movement provides few clues about what sleep stage we are in.”
Other studies have shown that many sleep tracking devices fail to differentiate one stage of sleep from another, based on body movement alone.
The fact that these devices are updated so frequently makes it hard for scientists to keep up with the claims and measure all the latest updates against proper polysomnography tests, while most companies won’t release the algorithms that they use to make predictions about sleep, which also makes it hard for claims to be tested.
What do we know?
Trackers that incorporate heart rate data tend to be slightly more accurate when measuring sleep duration because a person’s heart rate does fluctuate during different sleep stages, according to Dr Reid.
However, there are still wild differences between the accuracy of different devices even those that do incorporate heart rate data.
What we do know is that they may not help you if you have sleep problems.
Participants in one study had their sleep scores from their devices manipulated to show different results. While all the participants had the same amount and quality of sleep, those who were told they had a bad night’s sleep reported increased sleepiness and difficulties with thinking processes. Those who were told they had ‘good sleep’ showed the opposite.
“While sleep devices might be useful for those who have generally good sleep but are interested in tracking or establishing a better routine, people who have poor sleep or mental health conditions may want to avoid them,” Dr Reid said.
“The best metric for measuring how good your sleep was is to see how you feel each day. If you’re tired and struggling to concentrate, then going to bed a bit earlier each night may help you feel more rested – no device necessary.”
Do you have a sleep tracker? How do you use it to improve your sleep? Why not share your thoughts in the comments section below?
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