Fitness trackers bad at keeping tabs on how much energy we burn

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Is Your Fitness Tracker Putting You in Danger?

(Reuters Health) -- Fitness trackers may be a trendy way to monitor every step we take, but these gadgets are actually pretty bad at keeping tabs on how much energy we burn, a new study suggests.

READ MORE: New students have to wear Fitbits at this university

Scientists pitted 12 devices like the Fitbit Flex and Jawbone Up24 against two proven methods of monitoring energy expenditure -- locking people in a room to assess every calorie consumed and burned, or asking people at home to drink specially treated water that makes it possible to detect energy output with a urine test.

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Fitness trackers bad at keeping tabs on how much energy we burn
NEW YORK, NY - FEBRUARY 02: Fitbit Alta products on display as celebrity fitness trainer Harley Pasternak and stylist to the stars Anita Patrickson help introduce Fitbit Alta, a slim, sleek fitness wristband that can be personalized to fit your style, on February 2, 2016 in New York City. Fitbit Alta is designed with a satin finish, stainless steel body and features a line of interchangeable bands in multiple popular colors and premium materials. (Photo by Dave Kotinsky/Getty Images for FitBit)
NEW YORK, NY - FEBRUARY 02: Celebrity fitness trainer Harley Pasternak (pictured) and stylist to the stars Anita Patrickson help introduce Fitbit Alta, a slim, sleek fitness wristband that can be personalized to fit your style on February 2, 2016 in New York City. Fitbit Alta is designed with a satin finish, stainless steel body and features a line of interchangeable bands in multiple popular colors and premium materials. (Photo by Dave Kotinsky/Getty Images for FitBit)
NEW YORK, NY - FEBRUARY 02: Celebrity fitness trainer Harley Pasternak and stylist to the stars Anita Patrickson help introduce Fitbit Alta, a slim, sleek fitness wristband that can be personalized to fit your style on February 2, 2016 in New York City. Fitbit Alta is designed with a satin finish, stainless steel body and features a line of interchangeable bands in multiple popular colors and premium materials. (Photo by Dave Kotinsky/Getty Images for FitBit)
The Fitbit Inc. Blaze fitness tracker is unveiled during an event at the 2016 Consumer Electronics Show (CES) in Las Vegas, Nevada, U.S., on Tuesday, Jan. 5, 2016. CES is expected to bring a range of announcements from major names in tech showcasing new developments in virtual reality, self-driving cars, drones, wearables, and the Internet of Things. (David Paul Morris/Bloomberg via Getty Images)
SAN DIEGO, CA - NOVEMBER 14: Volunteers take part in Fitbit introduces Fitbit Local, free all-levels workouts led by talented community trainers. The launch in San Diego included a morning bootcamp and yoga session led by Sheri Matthews and Mike Sherbakov. Get Together. Sweat Together. (Photo by Robert Benson/Getty Images for Fitbit)
SAN DIEGO, CA - NOVEMBER 14: Volunteers take part in Fitbit introduces Fitbit Local, free all-levels workouts led by talented community trainers. The launch in San Diego included a morning bootcamp and yoga session led by Sheri Matthews and Mike Sherbakov. Get Together. Sweat Together. (Photo by Robert Benson/Getty Images for Fitbit)
HOLLYWOOD, CA - NOVEMBER 11: Professional Boxer Miguel Cotto trains with Fitbit Surge in preparation for his fight on Nov. 21 with Canelo Alvarez at Wild Card Boxing Club on November 11, 2015 in Hollywood, California. (Photo by JC Olivera/Getty Images for fitbit)
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In the first experiment, measurements from the fitness trackers deviated from the lab results in a typical day by underestimating energy expenditure by as much as 278 calories or overestimating by up to 204 calories. With the second experiment, the devices ranged from 69 to 590 calories lower than the urine tests.

The results are troubling because when fitness trackers overestimate exercise, people who need more exercise to maintain or lose weight might get too little activity, increasing their risk for obesity and other chronic health problems, said senior study author Motohiko Miyachi of the National Institute of Health and Nutrition in Tokyo, in an email.

Underestimating exercise might be just as dangerous for some people, said Dr. Adam Schoenfeld, a researcher at the University of California, San Francisco and author of an editorial accompanying the study in JAMA Internal Medicine.

"In healthy persons, use of fitness trackers may not be as risky, especially if the information collected is not used for medical decision-making," Schoenfeld added. "Still, even for healthy users, it may be difficult to promote health and wellness if these devices are proving inaccurate or variable feedback."

To test the accuracy of fitness trackers for monitoring energy expenditure, Miyachi and colleagues asked nine men and 10 women ages 21 to 50 to wear 12 different devices while participating in the two experiments.

Eight devices used in the experiments are popular with consumers in Japan: Fitbit Flex, Jawbone Up24, Misfit Shine, Epson Pulsense PS-100, Garmin Vivofit, Tanita AM-160, Omron CalorieScan HJA-403C, and Withings Pulse O2.

The other four gadgets have been validated in previous research: Panasonic Actimarker EW 4800, Suzuken Lifecorder EX, Omron Active style Pro HJA-350IT, and ActiGraph GT3X.

For the first experiment, participants went into what's known as a metabolic chamber, a room specially designed to monitor calories consumed and burned, for 24 hours. They got three meals, and they could work at a desk, exercise on a treadmill, watch television, do housework, and sleep while they were in the room.

In this airtight chamber, scientists can use a technique known as indirect calorimetry to assess energy expenditure by measuring carbon dioxide production and oxygen consumption.

Compared with these measurements, half of the fitness trackers underestimated energy expenditure and the rest overestimated it.

For the second experiment, each participant wore the devices for 15 days and collected urine samples on eight days. Every fitness tracker underestimated energy expenditure, the study found.

It's possible some of the underestimation might be due to people removing the devices to bathe or to charge batteries, the authors note.

In addition to the small size, other limitations of the study include its reliance on participants who weren't obese and who didn't have health problems that would limit their ability to exercise, the authors also note.

Still, the findings suggest that consumers may not have an easy time finding a reliable fitness tracker to monitor exercise, Schoenfeld said.

"It is currently quite challenging to tell which fitness trackers are accurate and reliable and which are not since there aren't much data available," Schoenfeld added. "These studies demonstrate that even the most popular applications and devices may be inaccurate or highly variable."

SOURCE: JAMA Internal Medicine, online March 21, 2016.

RELATED: Fitness tips to achieve success

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Fitness trackers bad at keeping tabs on how much energy we burn

1. Get the right gear. When it comes to workout gear, I need looks that are both stylish and functional. I can honestly say, when I love my gear, I'm more committed to my workout. I like looks that are light weight, breathable, stretchy material in bright colors and patterns. I recently completely feel in love with a high quality fitness line, Cory Vines. Their line is both durable, anti-bacterial, anti-ordor and very comfortable. My yoga classes have not survived without them as of late!

(Photo: Getty)

2. Talk about your resolutions. Make your goals known to both friends, family members and co-workers. When you're chatting with them often, they will likely ask about your progress and want to cheer you on!

(Photo: Getty)

3. Set small goal & celebrate your victories. Be sure to set smaller, attainable milestones as you progress throughout your plan and celebrate when you reach your goals. For example, if your goal is to lose 15 pounds in 5 months, set small

(Photo: Getty)

4. Track progress through a journal or mobile app. I love the My Fitness Pal App where I can track both my meal intake and fitness regimen. It keeps me motivated and more aware of the impact of my choices. There are plenty of free, user-friendly mobile apps available that make tracking simple, or consider starting a journal or making daily notes.

(Photo: Getty)

5. Have fun. Make your your fitness goals involve a little fun. If you love to run, choose a race that involves fun actives like the Dirty Girl Run or Rock & Roll Races. Similarly, if you love to bike, see if there is a club or temporary outdoor class you can take in your area to switch things up. The more fun the class or activity, the more likely your friends will join also.

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