The One Big Thing Fitness Trackers Don’t Do Very Well

Five fitness trackers were put to the test — which one fared the best? (Photo: Getty Images)

The next time you’re at the gym, glance at the wrists of those working out around you — chances are, you’ll spot a fitness tracker or few. 

It’s no surprise, considering an estimated 19 million devices were in use in 2014, according to the American Council on Exercise (ACE). But according to a small new study, these trackers may not be all that accurate at estimating calories burned — and some brands may be more accurate at tracking than others.

For the study, the American Council on Exercise commissioned researchers from the University of Wisconsin—La Crosse Clinical Exercise Physiology program to examine five popular fitness trackers: Fitbit Ultra, Nike+ Fuelband, Jawbone UP, Adidas MiCoach, and BodyMedia FIT Core.

Related: Will Fitness And Activity Trackers Really Make Us Healthier?

The goal of the study was to see how well the trackers measured the amount of calories burned (energy expenditure) and the number of steps taken. For the study, 20 men and women ages 18 to 44 wore the fitness trackers, as well as a portable metabolic gas analyzer and the NL-2000i pedometer to accurately measure steps and calories burned.

Study participants did two 50-minute exercise sessions wearing these devices. The first session involved walking for 20 minutes on a treadmill with no incline, resting for 10 minutes, and then running on the treadmill for 20 minutes. The second session involved 20 minutes on an elliptical cross-trainer that worked both arms and legs followed by a rest period, and then a series of agility drills, such as ladder drills, basketball free throws, and half-court lay-up drills.

Turns out, most of the devices either overestimated or underestimated the number of calories burned while exercising. For example, the portable metabolic gas analyzer the researchers used showed that the average number of calories burned running on the treadmill was about 240 calories, but Jawbone UP showed an average of 288 calories burned, while the BodyMedia FIT Core showed an average of only 210 calories burned.

The trackers also underestimated activity during the agility drills, which involve complex movements that are harder to track than simply steps taken. The devices fared much better (within 10 percent accuracy) when it came to calculating steps while walking and running on the treadmill, as well as exercising on the elliptical trainer. 

There wasn’t a single device that was head and shoulders above the rest when it came to calorie-burning accuracy, with devices varying in accuracy depending on the activity. Overall, the Jawbone UP did the best at accurately counting steps across multiple workouts, but the Fitbit Ultra seemed to come in a strong second place (it was accurate in tracking steps while the participants walked on the treadmill or used the elliptical trainer, but was less accurate when tracking agility-related movements). Meanwhile, for calorie counts, the fitness trackers were all over the map: For example, the Nike Fuelband was close to target with how many calories were burned while walking, but was off with calories burned while running, and way off with calories burned on the elliptical trainer.

Related: How Accurate Are Fitness Tracker Devices?

So does that mean you should toss your fitness tracker in the trash? No, Ted Vickey, ACE senior fitness consultant for technology, tells Yahoo Health. Vickey suggests taking the new findings with a grain of salt: “People use a weight scale at home, one at the gym and one at their doctor’s office. Each gives a different number. Which is accurate? We don’t have these same concerns with scales, so why with a step tracker?” Instead, it’s important to focus on the relative number provided by the fitness tracker, than an absolute number, he explains. “If one uses the same tracker over time, then for all intents and purposes, it is accurate. It is about setting a baseline and then working from there,” he says.

Plus, Vickey notes that fitness trackers provide valuable insight into overall physical activity during the day, not just during exercise sessions. “I hope that we begin to redefine exercise to not just include what we do at the gym but what we do during the day — namely, physical activity,” he says.

Kelvin Gary, personal trainer and owner of Body Space Fitness in New York City, says that fitness trackers are beneficial, even with their limitations. “They don’t always show a true representation of activity level,” he says, “but we always ask our clients to have a goal and these devices are great for setting activity-based goals.”

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