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Fitness Trackers and Weight Loss
Is your fitness tracker lying to you?

Wearable Warnings
Can you trust your fitness tracker?

Over the last few years, devices designed to digitally track fitness levels have gone mainstream. The Fitbit, Samsung Gear and Apple Watch are just a few examples. More than 34 million fitness trackers or “wearables” shipped just in the last quarter of 2016. Millions of people are now relying on these devices to tell them what’s happening with their bodies.  

Fitness trackers use multiple data points like heart rate, accelerometers (which measure how fast they’re moving), gyroscopes (to track orientation and rotation speeds), GPS signals (to track where you’re going) and even the heat your skin gives off. All this information is combined differently by each company to try and guess what you’re doing and how it’s affecting you.

Generally, the more information we have, the better decisions we can make. When a fitness tracker I’m wearing says that I’ve burned off 1,000 calories in a day, it’s reasonable to expect me to use that information when I’m deciding what to eat. So researchers decided to compare weight loss using traditional methods, versus ones that were “technology-enhanced.” The theory was that wearables would give people on a diet an advantage when trying to lose weight.

The good news is that after two years, “Both groups had significant improvements in body composition, fitness, physical activity, and diet…” So going on a diet with or without a fitness tracker helped the participants. The surprising part was that, “Among young adults with a BMI between 25 and less than 40, the addition of a wearable technology device to a standard behavioral intervention resulted in LESS weight loss over 24 months.”

What that means is that those fitness tracking devices, didn’t give any advantage over traditional weight loss methods, they performed WORSE. How could that be?

It took another study published in the Journal of Personalized Medicine, May of 2017 to clear things up. Researchers decided to test the ACCURACY of seven major fitness trackers including the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn, and Samsung Gear S2.

Apple WatchBasis PeakFitbit SurgeMicrosoft BandMio Alpha 2PulseOnSamsung Gear S2

The study used traditional (and proven) methods of measuring heart rate and energy expenditure, and then they compared those results to what the fitness trackers were saying. When it came to things like how much energy someone was using, the best wearable was off by 20% and the worst was off by an average of 93%. The devices were so bad at figuring out how many calories a person burned (their energy expenditure) that the researchers said, “none of the devices provided estimates of energy expenditure that were within an acceptable range in any setting…”

Suddenly the failure rate of wearables to help people lose weight was understandable. If you finish a run and your fitness tracker says you just burned 1,000 calories, you might want to reward yourself with a 500-calorie treat. But if your REAL energy expenditure was only 500 calories (not 1,000), your reward just eliminated any weight loss benefit of that run.

It’s important to understand that there will always be some margin of error when using any kind of device like this. But error rates of between 5% and 10% are considered acceptable, not 20% to 93%. According to the study, “The Apple Watch achieved the lowest overall error in both Heart Rate and Exercise Expenditure, while the Samsung Gear S2 reported the highest.”

Digging deeper into the data, you find that the error rate changes based on who’s using the devices. The highest error rates were for males, people with greater body mass index, anyone with a darker skin tone and people walking. The greatest accuracy was for light-skinned women who were already in good shape.

None of this means you should toss your wearable out. Instead, treat the information with a healthy dose of skepticism. Then use the data to chart your progress over time. Are you going further? Faster? Burning more calories? Ignore the total calories it claims you’re burning and strive to keep pushing yourself, based on your previous readings.

Studies Referred to in this Article

JAMA Original Investigation
Effect of Wearable Technology Combined With a Lifestyle Intervention on Long-term Weight Loss - The IDEA Randomized Clinical Trial
John M. Jakicic, PhD; Kelliann K. Davis, PhD; Renee J. Rogers, PhD; Wendy C. King, PhD; Marsha D. Marcus, PhD;
Diane Helsel, PhD, RD; Amy D. Rickman, PhD, RD, LDN; Abdus S. Wahed, PhD; Steven H. Belle, PhD
September 20, 2016

Journal of Personalized Medicine
Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort
Anna Shcherbina 1,†, C. Mikael Mattsson 1,2,†, Daryl Waggott 1,3,†, Heidi Salisbury 3,
JeffreyW. Christle 1, Trevor Hastie 4,5, Matthew T. Wheeler 1,3 and Euan A. Ashley 1,3,5,*
Received: 27 February 2017; Accepted: 4 May 2017; Published: 24 May 2017

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