According to Gartner analysts, hopes that consume buy 86 million smart watches in 2020. It is a $ 23 billion market globally. Beyond physical activity and sports, a major factor that causes people to buy these stylish wrist computers is the ability to control sleep.
This is an almost universal feature, found even on the cheapest devices. But why would you want that? Most importantly, does sleep tracking really work?
How sleep trackers work
Hidden inside the sleek Apple Watch or Samsung Galaxy Watch are a series of sophisticated motion trackers that can detect even the slightest movement with a decent amount of accuracy.
These sensors (especially the accelerometer) form the basis of the portable sleep tracking system, and the movement of your body serves as an indicator of whether or not you are asleep. This approach has a complicated scientific name, actigraphy, but it is simpler than it seems.
When you fall asleep, your body becomes prone, making much less movement than it would when you were awake. This gives the portable device the main indicator that you are asleep.
As you progress through the various stages of the sleep cycle, your body behaves in different ways, allowing the wearable device to track whether you are sleeping lightly or deeply.
The first two stages of the sleep cycle are the easiest. During these periods, your body may contract involuntarily. These movements are called «hypnotic jerks» and are a type of movement called myoclonus. According a study published in the October 2016 article in the journal Sleep MedicineThese movements take place randomly and are spread between 60 and 70 percent of the population.
As you enter the deeper stages of sleep, your body movements slow down, giving your wearer a decent barometer of where you are in your sleep cycle.
Finally, there is REM sleep (or rapid eye movement), which is the part where you normally experience dreams and nightmares. In this part, your body is the most immobile.
Your heart is the most nervous muscle of all
It is worth noting that many portable devices contain heart rate monitors, which can improve the accuracy of sleep tracking. This is because the heart rate varies greatly between different stages of sleep.
During light sleep, your heart rate slows down slightly, only to return to normal when you fall into a deep sleep. The activity of the heart increases even more as you start dreaming, and the breathing also becomes irregular.
While standard sleep trackers based on actigraphy can tell you when you are sleeping, devices with heart rate monitors are better able to provide a qualitative analysis of your sleep, telling you how restful your sleep is.
Are sleep trackers accurate?
When investing in a smart watch, keep in mind that sleep tracking technology is not perfectly accurate. After all, they are products for lifestyle and not precise medical devices.
A study, published in the June 2019 issue of al JMIR mHealth and uHealth Magazine, looked at the accuracy of the Fitbit Charge 2, especially compared to a medical grade tracker. I found that FitBit had a tendency to overestimate how long an individual has been in a deep sleep state, underestimating when the user has moved to another stage.
In general, the medical literature tends to be quite critical of consumer sleep trackers, especially when it comes to the methodology used to achieve their results.
A Technology Review 2015, published by researchers at Johns Hopkins University School of Medicine, looked at several of the leading trackers of the time. Of the six devices examined, only one provided information on the accuracy of their sensors, while two provided information on how they interpreted this data to produce results.
What will you do with this data?
Another criticism of sleep tracking devices is that they often do not guide people on how to do this. improve sleep quality; save the obvious advice basic sleep hygiene. For example, a sleep tracker might recommend increasing the amount of exercise you do during the day or avoiding the use of electronic devices before bed.
An article, published by academics at the University of Tokyo and the University of Technology in Queensland, claims that Consumer sleep tracking technology does not provide long-term benefits. The study also argued that sleep trackers should use more sophisticated health and lifestyle data in their values to be useful.
So is it worth it?
Finally, the results produced by smart watch sleep tracking technology should be considered purely informative. They are not diagnostic tools.
If you think you have a sleep disorder, you should talk to your doctor, who can coordinate a rigorous and controlled sleep study using the most sophisticated medical equipment.
If you decide to invest in a smart watch to keep track of your sleep quality, it’s important to get one with a built-in heart rate monitor, such as a FitBit Versa 2 or a Apple watch, what’s wrong with her third-party applications that can track your sleep. The analysis published by Johns Hopkins was somewhat appalling about the accuracy of devices that use actigraphy as the only method of monitoring.