Jung-Min Lee, PhD
Jung-Min Lee, PhD, assistant professor, Physical Activity and Health Promotion Laboratory, University of Nebraska, Omaha. His study was published in Medicine and Science in Sports and Exercise.
Can a relatively inexpensive little device that you wear actually tell you how much exercise you’re getting and how fit you are? That’s what products called fitness trackers—with brand names like Jawbone, Fitbit, NikeFuel and Misfit—promise to do. The idea is that you wear one of these lightweight, computerized sensors (also called activity trackers) on your body or clothing, and it records when you’re moving and how you’re moving, so that you can learn whether you’re getting enough exercise and burning enough calories…or if you should raise the bar on your activity level.
Some fitness trackers are designed to be worn on the wrist, some around the upper arm or as a pendant or a waist clip. Such devices were once used only in research settings, but consumer models are growing in popularity, generally costing between $50 and $150.
But do they really work?
Not precisely, according to several different studies that evaluated different models. But that doesn’t mean they’re useless, said Jung-Min Lee, PhD, assistant professor of physical activity and health promotion at the University of Nebraska. He recently conducted a study that evaluated eight different fitness trackers that claim to use a technology called indirect calorimetry, a measurement of energy—or calorie—expenditure that uses oxygen consumption as a gauge. The eight trackers included BodyMedia FIT, which is a band worn on the upper arm, DirectLife, which can be worn around the neck (or carried in a pocket or attached to a belt), the Fitbit One, Fitbit Zip and ActiGraph, which are all belt clips, and the Nike+Fuel Band, Jawbone UP and Basis B1 Band, which are wristbands.
These eight commercially manufactured trackers were compared with a professional indirect calorimetry device (a unit used in university, government and commercial research) in 60 healthy men and women who wore all of the trackers and the indirect calorimetry device simultaneously. (Sounds fun, actually, doesn’t it?!) The study participants, decked out in their array of trackers, performed a series of activities that lasted for a total of 69 minutes. They walked on a treadmill at different speeds, reclined, used a computer, ran at different speeds, went up and down stairs, played basketball, and rode a stationary bike. All this time, each device was (supposedly) measuring how many calories the participants burned.
The results: According to the professional-grade indirect calorimetry device, the average energy expenditure was 356.9 calories, but the average of readouts from the various consumer fitness trackers ranged from 271.1 calories for the Basis B1 Band to 370.1 calories for the Fitbit Zip. Although no consumer tracker hit the nail on the head, all except the Basis B1 Band came within a relatively acceptable margin, with error ratings ranging from 9% to 13%. The BodyMedia Fit, Nike+Fuel Band and Fitbit Zip were closest in accuracy to the indirect calorimetry device.
Although Dr. Lee proved that these consumer-grade fitness trackers are only “OK” when it comes to accurately counting calories burned, he still thinks they can be worth the money—as do I—but with certain caveats. Reason: “Trackers are great motivational tools,” he said. “Almost all trackers have goal-setting features that allow you to program your desired activity level into them. The tracker will then give you feedback, via communication with your smartphone or whatever other electronic device you’ve synced it with, to keep you motivated.” For example, if you’ve set a goal to walk 6,000 steps in a day but the monitor determines that you’re sitting down, you might get a gentle reminder via e-mail or smartphone to get moving.
And even if your tracker is off by 5% or 10% or so on your calories burned, it’s OK because you are also going to use your eyes and your common sense when it comes to assessing your fitness. If your tracker tells you that you are burning the same number of calories that you believe you are eating, but you are still gaining weight…well, c’mon, you know what to do, right? Eat less and/or exercise more—it isn’t rocket science.
Many trackers also include bells and whistles that allow you to, for example, calculate how many calories you’re eating per meal, tally up total activity time or distance traveled (yes, like a good old-fashioned pedometer) or even add up how many calories you’ve burned while sleeping, though I wouldn’t depend on snoozercise for fitness.
There’s also a style factor. Most wristbands look more like high-tech watches or jewelry than fitness gadgets. And some trackers, such as Misfit, are waterproof so that they can literally be worn all the time.
Still, about one-third of people who get fitness trackers no longer wear them after three months. Dr. Lee attributes at least some of this loss of interest to purchase of a model that’s uncomfortable to wear or otherwise fails to meet a user’s expectations.
“My recommendation for anyone who wants to use a fitness tracker is to get as much information as possible about different models,” Dr. Lee said. Carefully peruse online reviews of actual users to get the pros and cons, and comparison shop at sites such as TopTen REVIEWS, which list and rate features, side by side, of the most popular models. “Then go to a store that carries several brands to try them on and see how they feel.”
