Study raises questions over wearable fitness trackers


I don't know about you, but I've been rather sceptical of fitness wearables for some time now. It all started about three years ago when I was reviewing a particular device and noticed that it counted me blow-drying my hair as steps. 

Since that time I have approached every wearable with an arched eyebrow, waiting for it to prove itself rather than impress me with bells and whistles. There is no denying that many of these devices look good, but what is the point in wearing one if they don't do what they're meant to?

New research, conducted by Stanford University's School of Medicine, tested the accuracy of wristband activity monitors including the likes of the Apple Watch and Fitbit's Surge. These devices were tested along with Basis Peak, Microsoft Band, Mio Alpha 2, PulseOn and Samsung Gear 2  by a group of 60 volunteers. 

Their findings showed that devices claiming to measure energy expenditure are likely to be out by a "significant amount". Devices that measure heart rate performed well. Six of the seven wearables tested measuring the user's heart rate only showed an error rate of less than 5%. 

Apple Watch proved to be the most accurate of the seven devices tested in terms of heart rate. The error rate sat at 2%, while Samsung's Gear S2 had the highest error rate, at 6.8%. 


Not every wearable sold has a heart-rate monitor. Many of the low-end devices act as a pedometer and sleep monitor. They have an accompanying app that illustrates information beautifully, but does Joe Soap on the street know what that information means or how to use it?

I know that I don't. 

The study's senior author Professor Euan Ashley said:  

"Manufacturers may test the accuracy of activity devices extensively, but it's difficult for consumers to know how accurate such information is or the process that the manufacturers used in testing the devices."

"The heart rate measurements performed far better than we expected, but the energy expenditure measures were way off the mark. The magnitude of just how bad they were surprised me."

While the team could not quite explain why the energy expenditure measurement was so off, one researcher suggested that heart rate is directly measured, while energy expenditure is calculated indirectly through proxy calculations. 

The researcher, named Anna Shcherbina, continued to explain the difficulty associated with measuring energy expenditure, “It’s very hard to train an algorithm that would be accurate across a wide variety of people because energy expenditure is variable based on someone’s fitness level, height and weight.”

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