Precise Devices: Fitness Trackers Are More Accurate Than Ever
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Fitness trackers are getting better and better at what they’re primarily designed to do: count your steps and measure your heart rate.
Most of the trackers we test now earn a top score in step counting, and models that measure heart rate are generally excellent at that, too. What’s more, the step-count feature now built into many smartwatches and smartphones also fared well, we found.
But beyond technical proficiency, will trackers help you reach the goals you have for using one? Things that, presumably, include being more active, losing weight, and feeling healthier.
For some people, the answer is yes, according to a nationally representative Consumer Reports survey of 1,007 U.S. adults—though the survey also makes it clear that you can’t expect miracles.
Instead, our survey suggests—and experts we spoke with agree—that you should view trackers as one tool in a comprehensive effort to be more active, lose weight, and improve your health. (Find out whether counting your ZZZ’s will improve your sleep.)
Tiny Technical Marvels
Today’s trackers pack an impressive array of sophisticated electrical components. These include accelerometers to detect the slightest of body movements, LEDs that flash light through your skin to measure blood flow, galvanic sensors that measure changes in electrical connectivity caused by sweat, gyroscopes that sense when you stand up or lie down, GPS receivers that can track how far you walk or run, and altimeters that show changes in elevation.
Together, those features allow fitness trackers to not just count steps but also to estimate your heart rate, exercise intensity, flights of stairs climbed, hours slept, and calories burned.
Though sales of dedicated fitness trackers are waning—market leader Fitbit expects revenue to drop by about 22 percent this year compared with last—activity tracking is still big business, with that company alone projecting revenue of up to $1.7 billion in 2017.
Smartphones, which now count steps, and smartwatches, which also track heart rate, are picking up the sales slack. Trackers are also increasingly being fashioned into less obtrusive designs, such as necklaces, or being incorporated into other products, like headphones. (Read “Is a Smartphone or Smartwatch a Good Enough Tracker?” for more on the pros and cons of some of those alternatives.)
Moving Targets
The idea behind fitness tracking is that knowledge is power—knowing how many steps you take each day can encourage you to take more of them.
Though trackers do seem to help make some people be more active, it’s clear that doesn’t happen automatically. For example, a 2016 study of 800 Singaporeans in The Lancet Diabetes & Endocrinology—one of the longest, largest, and best-designed studies to date—found that after a year, people using trackers walked an average of just 37 additional minutes each week.
Not surprisingly, most people in that study neither lowered their blood pressure nor lost weight.
One reason the devices don’t seem to help much when it comes to weight loss could be that their calorie-counting feature—which uses factors such as activity level, gender, and weight to estimate how much energy you burn—may not be very accurate.
We have not tested that, but Stanford University researchers recently did. They took precise metabolic measurements from 60 volunteers and compared results with estimates from seven fitness trackers. All of the devices were off by at least 27 percent, and the least accurate was off by 93 percent.
Secrets to Success
So why do trackers seem to help some people but not others? Our survey, plus interviews with experts, uncovered some strategies that can help you get more out of your device.
Be social. Using the devices with others can be a powerful motivator. Fitbit says that people who use the devices with online friends log an average of 700 more steps per day than those who go solo. Wendy Beck agrees, competing with other users in virtual challenges. “It just makes me get up and move,” Beck says.
Reward yourself. Financial or other incentives might also help, says Mitesh Patel, M.D., at the Penn Medicine Center for Health Care Innovation, Perelman School of Medicine in Philadelphia. That can be especially true when you’re starting. He recommends trying an app that gives cash rewards for meeting your goals. One such app is StickK, a program developed by behavioral economists at Yale University that lets you set a goal and a monetary stake and have a friend enforce it.
Keep it simple. Eric Topol, M.D., a cardiologist and digital-medicine researcher at Scripps Research Institute in La Jolla, Calif., tells patients that if they don’t want another electronic device in their lives and don’t want to track their heart rate, they can just use their smartphones to count their steps.
Think in bouts. Many trackers now allow users to schedule “Move” alerts after every, say, 30 minutes of inactivity. And research suggests that long periods of sitting can be especially harmful.
Watch what you eat. If you want to lose weight, diet is key, no matter how much you exercise or which device you use. “You can never out-train a bad diet,” says Ross Steiner of Steiner Strength in San Francisco. “I don’t care how many steps you do.”
And resist the urge to use a workout as an excuse to splurge on a big meal, he says. Though the calorie-counting feature on trackers may not be very accurate, many pair with apps, such as MyFitnessPal, that have food databases, allowing you to record what you eat. That could make you more conscious of what you eat and prompt you to make wiser food choices.
Stick with it. Our survey and other research suggest that many people give up on trackers within a few months. But more than a quarter of people in our survey who currently wear their device have been using it for one to two years, and 16 percent have been using it for more than two. So if you can force yourself to stick with a tracker through that initial period, using the device—and regular exercise—could be more likely to become a lifelong habit.
Will Counting Your ZZZ’s Improve Your Sleep?
Some trackers are claimed to record how much and how well you sleep by measuring your bedtime tossing and turning plus your heart rate. That information, the theory goes, can help sensitize you to your sleep patterns and help you sleep better as a result.
Fitbit, for example, worked with Stanford University scientists on software that uses your sleep data to estimate how much time you spend in light vs. deep sleep and to develop advice designed for you.
But experts we consulted aren’t convinced. For one thing, trackers don’t reliably “differentiate between quiet wakefulness and light sleep,” says Kelly Baron, Ph.D., at Rush University Medical School, who wrote about trackers in the Journal of Clinical Sleep Medicine. As a result, they may overestimate sleep.
And even if the trackers are accurate, they may not always help people sleep better. For example, Baron says that although the devices may encourage some people to make good sleep more of a priority, or to talk with a doctor, they could also unintentionally worsen sleep by making you overly anxious about getting enough of it. And, she says, they can even foster bad sleep habits, such as lying in bed even when you’re not tired.
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