Do Fitness Trackers Really Improve Your Health?

Millions of Americans now wear fitness bands on their wrists to count their steps daily. Some employers are using fitness trackers to set goals—and rewards—for employees. Health and life insurers are offering premium discounts for wearing one. School systems are even using them to enable self-directed physical education programs.

How accurate are they? Fitness bands contain an accelerometer, which tracks movement in every direction to calculate the number of steps you’ve taken. But studies show that over the course of a day, many trackers have error rates of 10% to 20%. Tufts University’s Health & Nutrition Letter suggests you verify that your stride-length setting is correct by going to a track with the exact distance marked and counting your steps as you walk it. If you walk, say, 100 feet in 40 steps, divide 100 by 40. You have a stride length of about 2.5 feet.

Most fitness bands are on track when it comes to counting steps when you’re walking, running or climbing stairs—usually coming within 1% to 4% of your actual step count, says Alex Montoye, an assistant professor at Alma College who studies wearables. The devices are also good at not awarding credit for stationary activities with a lot of wrist movement, such as typing or shuffling papers.

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But the trackers fall short when it comes to measuring your activity as you’re doing household chores, such as sweeping, washing dishes, cleaning or gardening. According to Montoye’s recent study at Ball State University, most fitness bands underestimate the amount of calories burned when doing tasks around the house by 27% to 34%. Also worth noting: The bands often fail to capture your steps when you’re pushing a grocery cart, lawn mower or baby stroller; if you want credit for those exertions, consider slipping the band into a pants or skirt pocket.

Before you choose a fitness tracker, consider the features you’re looking for. A simple step counter, such as the Fitbit Zip or Jawbone UP Move, will run you $50 to $60. At the high end, the Fitbit Surge ($250) will not only count steps but also track your heart rate and sleep patterns—plus it offers GPS tracking and has a 1.25-inch screen to alert you to text messages sent to your smartphone. If you want to measure your heart rate and monitor your sleep but don’t need the other advanced features, consider the Fitbit Charge HR ($150) and the Jawbone UP3 ($130). (The Apple Watch has a built-in workout application to track your activity, and you can load a sleep-monitoring app from the iTunes store.)

Virtual coaching. Despite missteps when it comes to recording your activity, wearable trackers can be useful for improving your daily workout. Because the majority of adults’ exercise comes in the form of walking, says Montoye, your step count should provide a good ballpark of your daily activity.

And for many fitness-band wearers, the precise number of steps logged matters less than the motivation to get up and move around. The bands can fuel competition to outwalk friends and encourage couples to take an evening walk. According to Harvard Women’s Health Watch, numerous studies have focused on activity levels of women older than 50. Those who wore fitness trackers significantly increased the time they spent doing moderate to vigorous activity.