Wearable fitness trackers aren’t useless

Such devices aren’t taken seriously by many, but they are indeed bringing about a change in the fitness industry, experts say

Wearable fitness trackers will be on many Christmas shopping lists this year, with a vast range of devices (and an ever-increasing number of features) hitting the market just in time for the festive season. But what does the latest research say about how effective they are? Getting the basics right: Firstly, a multitude of studies have looked at the accuracy of wearable fitness trackers for measurements related to physical activity, including step counts, heart rate and number of calories burned. They show step counts are generally highly accurate, while heart rate and calories burned are reasonably accurate.

When study participants wear two different activity trackers at the same time, the numbers of steps, minutes of activity and calories burned aren't exactly the same, but they are correlated. That is, when one goes up so does the other, and vice versa. This suggests they are generally capturing the same information, albeit with slightly different sensitivity. Evidence for sleep tracking is a little patchier. Wearables are pretty good at detecting bed time, wake time and overall sleep duration. But estimates for more technical metrics such as the “phases” of sleep — such as REM sleep — don’t marry with medicalgrade measurements taken by polysomnography.

Going beyond the basics: In a 2019 Apple-sponsored study reported in the New England Medical Journal, 419,297 participants without known atrial fibrillation wore an Apple Watch. During the study, 2,161 of them received an irregular pulse notification, of which 84% were subsequently confirmed to have atrial fibrillation (an irregular and rapid heart beat). This is a serious medical condition that requires treatment to prevent stroke. The ability to alert users of a potential undiagnosed cardiac condition seems highly beneficial. Although, others have cautioned the Apple Watch can also miss cases of undiagnosed atrial fibrillation — which emphasises the importance of never relying on wearable metrics for medical purposes. Another study published in September reaffirmed the Apple watch’s electrocardiogram feature can detect serious cardiac irregularities. A similar study is currently underway to evaluate Fitbit’s electrocardiogram feature, but results aren’t out yet. Building a more advanced tracker: In terms of detecting falls (which would be very useful for older individuals), scientists

are developing wrist-worn devices that can accurately do this using accelerometer technology, which is the same underlying technology already used by wearables.

Meanwhile, the newest 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 bioelectric impedance analysis. When the

user touches the watch with their opposite hand, it passes a weak electrical signal through the body and back to the watch. The body composition is then calculated using algorithms and the manually entered body weight. At this stage, there’s no data in the scientific literature to support the accuracy of these measurements, so we’d recommend taking them with a pinch of salt.

Efforts will pay off: That’s the run down on 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-analyses (which involve combining results of multiple studies) suggest the devices are effective in helping people become more physically active and lose weight. A meta-analysis of 35 studies in various chronic disease populations suggested users added around 2,100 additional steps per day after they started using a wearable activity tracker. Other meta-analyses have suggested weight loss in the order of 1 to 1.5 kilograms, on average, over the duration of the studies.

Accuracy and effectiveness aside, wearable users typically report being satisfied with their devices. So if you happen to get for Christmas, keep in mind it could help with those New Year’s fitness resolutions.

—PTI