You wear your fitness tracker all day, to the gym and even in your sleep to keep an eye on your activity, heart rate and calories burned. But how accurate is this wearable technology?
A new Stanford University study suggests that fitness trackers are incredibly accurate when it comes to monitoring heart rate, but they’re way off when it comes to tracking energy expenditure and calories burnt, regardless of what activity you’re doing.
Previous studies have suggested they’re not bad at tracking steps as a pedometer, though.
“But conversely, we’re quite disappointed with the energy expenditure measurements. None of these devices were accurate, not even to a clinical standard but really to an everyday use standard,” she warned.
The experts were hoping for a 10 per cent error, at most. Instead, they saw errors ranging from 27 per cent to a steep 93 per cent when it came to tracking energy expenditure.
It wasn’t consistent either. Some gadgets overestimated calories burnt while others were underreporting. But the overall trend was underreporting, which means you could be burning more calories than you think you are.
For her study, Shcherbina worked with a group of 60 volunteers who wore four devices at any given time. The six devices used in her study include:
- Apple Watch
- Basis Peak
- Fitbit Surge
- Microsoft Band
- Mio Alpha 2
- Samsung Galaxy Gear S2
Turns out, the devices nailed heart rate. The error was within only five per cent for all types of activity.
The most accurate device was still 27 per cent off when it came to energy expenditure, though.
Factors, such as skin colour and body mass index even played a role in the measurements.
Shcherbina and her team couldn’t say why energy expenditure is so off. Each device uses its own algorithm for calculating energy expenditure – their formulas may not fit every individual perfectly, they guessed.
Heart rate, on the other hand, is measured directly and without as many factors at play.
This isn’t the first time scientists have warned about the inaccuracies of fitness trackers.
Last year, Japanese researchers stacked 12 devices against each other and learned that they’re way off in tracking calories, to the tune of up to 278 calories.
Half of the fitness trackers would overestimate calories burned by about 204, while others underestimated by up to 278.
A 2015 study, conducted out of North Carolina’s RTI International, zeroed in on Fitbit and Jawbone (Nike was included initially, until the company said it was moving out of the wearable tech sector).
Dr. Robert Furburg, a senior clinical informaticist at RTI, said he and his team pored over thousands of studies on fitness trackers and narrowed their review down to 23. They wanted to figure out the validity and reliability of trackers’ functions, such as steps, calories burned and sleep monitoring compared to lab-designed equipment that costs thousands of dollars.
Trackers were best at accurately measuring steps as a pedometer.
It makes sense that steps were the only accurate measurement. These devices don’t look at calories burned and calories consumed – they infer this information based on how many steps you’ve taken and how much distance you’ve logged, he said.
“Steps taken is frequently the only actual variable being measured on the device and how these other numbers are reached is a mystery to us as consumers,” Furburg said. If 10,000 steps is roughly 5.5 miles, that would be roughly 1,300 calories, he said as an example.
“Calories burned can be estimated based on your age in years, height, weight, gender and how many steps you’ve taken. All of that is plugged into an ugly equation that spits out a number. That’s where we find the greatest inaccuracies, taking steps away from the primary source,” he told Global News.
These errors could lead to issues with weight loss – if you think you’re working out enough to create a calorie deficit, you could be way off. You might indulge in more snacks too if you think you’ve worked off 200 more calories than you really have.
A Fitbit spokesperson says that the company performed its own internal studies to test its products.
“FitBit trackers are designed to provide meaningful data to our users to help them reach their health and fitness goals, and are not intended to be scientific or medical devices,” the spokesperson said in an email to Global News.
“The success of Fitbit products comes from empowering people to see their overall health and fitness trends over time – it’s these trends that matter most in achieving their goals,” the statement said.
Shcherbina’s full findings were published Wednesday in the Journal of Personalized Medicine.