By Ben Singh and Carol Maher for The Conversation
Wearable fitness trackers will be on many Christmas shopping lists this year, with a variety of devices (and more and more features) hitting the market just in time for the holiday season.
But what does the latest research say about how effective they are?
Fitness trackers are trendy
Currently, around one in five Australians owns one of these wearables, and around a quarter use a mobile app or website to monitor their activity level and health. Sales growth is forecast for the next five years.
The market landscape is changing rapidly. Fitbit and Garmin were market leaders for years. But Australians now prefer Apple watches (which are used by 43 percent of wearable tracker owners) over Fitbit (35 percent) and Samsung watches (16 percent) over Garmin (13 percent).
So far, fitness trackers are mostly used by younger people: around one in four Australians aged 20 to 40 report using one, compared to just one in ten people aged 60 or older.
However, manufacturers are on a mission to change that by adding features that allow users to monitor not only their fitness activities, but several other aspects of their health as well.
For example, the latest wearable models from all the leading manufacturers claim to measure a wide variety of medical readings like blood pressure, body fat levels, oxygen levels in your blood, your heart activity and even know when you are falling (with a feature that lets you call for help) .
Wearables get the basics right
First, a variety of studies have examined the accuracy of wearable fitness trackers for measurements related to physical activity, including step count, heart rate, and number of calories burned. They show that step counts are generally very accurate, while heart rate and calories burned are reasonably accurate.
When study participants wear two different activity trackers at the same time, the number of steps, minutes of activity, and calorie consumption are not exactly the same, but they do correlate.
That means, if one goes up, so does the other and vice versa. This suggests that they are generally capturing the same information, albeit with slightly different levels of sensitivity.
The evidence for sleep tracking is a little more sketchy. Wearables are pretty good at detecting bed time, wake time, and total sleep time. But estimates for more technical metrics like the “stages” of sleep – like REM sleep – are inconsistent with medical measurements made through polysomnography.
Sometimes wearables go beyond the essentials
In a 2019 Apple-sponsored study reported in the New England Medical Journal, 4,19,297 participants with no known atrial fibrillation wore an Apple Watch. During the study, 2,161 of them received irregular heart rate alerts, 84 percent of whom had post-atrial fibrillation (an irregular and fast heartbeat) confirmed.
This is a serious condition that requires treatment to prevent stroke. The ability to alert users to a potentially undiagnosed heart condition seems very useful. However, others have warned that the Apple Watch can also miss cases of undiagnosed atrial fibrillation – underscoring the importance of never relying on wearable readings for medical purposes.
Another study published in September again confirmed that the Apple Watch’s electrocardiogram function can detect serious heart irregularities. A similar study is currently being conducted to evaluate Fitbit’s electrocardiogram function, but the results are not yet available.
Building a more advanced tracker
In terms of fall detection (which would be very useful for the elderly), scientists are developing wrist-worn devices that can do it precisely using accelerometer technology, which is the same underlying technology already used by wearables. So the technology is there, but at this point it is unclear whether the promising lab results translate into accuracy in commercial wearables.
Meanwhile, the latest Samsung watch claims to measure blood pressure and body composition (such as fat mass, muscle mass and bone mass). Body composition is measured using a method called bioelectrical impedance analysis.
When the user touches the watch with the other hand, it sends a weak electrical signal through the case and back to the watch. The body composition is then calculated using algorithms and the manually entered body weight.
As of this writing, there is no data in the scientific literature to prove the accuracy of these measurements, so we recommend that you use them with caution. On the other hand, just a few years ago, the same criticism of electrocardiogram measurements from wearables was voiced – and these have subsequently proven to be justified.
Evidence says your efforts are paying off That’s the lack of accuracy, but do fitness trackers make a difference in people’s lives?
Hundreds of studies have used wearable activity trackers to try to increase physical activity in various general and patient populations. Meta-analyzes (combining the results of several studies) suggest that the devices are effective in helping people become more physically active and lose weight.
A meta-analysis of 35 studies in different populations with chronic conditions found that users added about 2,100 extra steps per day after starting to use a portable activity tracker. Other meta-analyzes have suggested weight loss on the average of 1 to 1.5 kilograms over the duration of the studies (the duration varying between studies).
And studies specifically looking at step tracking over long periods of time suggest that the benefits achieved linger (albeit less) for up to four years after first wearing the device.
Aside from accuracy and effectiveness, wearable users generally say they are happy with their devices. So if you happen to have one in your Christmas stocking this year, keep in mind that it might help with your New Year fitness resolutions.
(Singh is Research Associate, University of South Australia; Maher is Professor, Medical Research Future Fund Emerging Leader, University of South Australia)
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