Harvard Women's Health Watch

How fitness trackers can improve your health

The wearable electronic devices may motivate you to stick to a diet or exercise plan.

If you've resolved to get more exercise, lose weight, or get more sleep in 2016, then a host of wearable electronic devices and apps are available to help you succeed. They will gently prod you to work toward your goal, encourage you along the way, and praise you when you get there. The gadgets record your activity, while the apps interpret the results and send you frequent messages to let you know how well you're progressing.

And they seem to be effective, according to a small study. A randomized controlled trial of 51 overweight postmenopausal women found that those who wore a digital tracker exercised 38 minutes more a week than those who used pedometers. The results, published in the September 2015 issue of the American Journal of Preventive Medicine, aren't too surprising to Dr. Lauren Elson, a physiatrist at Harvard-affiliated Massachusetts General Hospital. "I have several patients who are using them successfully to get started on a walking program or to remind them when they are sitting too long," she says.

What the trackers do

The trackers, which are worn on a belt or wrist, rely on accelerometers—devices that detect the body's movement and convert it into data. The data are sent to an application on a smartphone, tablet, or computer, where software computes the number of steps taken, distance traveled, or calories burned. All count the steps you take every day, and most also track the duration and intensity of your activity and estimate calorie use. A few have alarms to remind you to get up and move around when you have been sitting too long. Some also log the minutes you spend sleeping, tossing and turning, and waking during the night. Additional features, such as heart rate monitors and altimeters—which measure elevation climbed—are available on some of the more expensive devices.

While the devices themselves give you a little information about your workout—they may display a digital reading of your heart rate, step count, or miles logged—the apps offer a wealth of additional data. For example, most generate graphs with detailed data on your steps, exercise intensity, and sleep behavior. They can give you an idea of when in the day you put in the most exercise, or the times during the night when you were restless or awake. They also allow you to compare your performance from day to day and week to week.

How they might aid weight loss

Many devices can replace the calorie logs and activity journals many dieters maintain to reach their goals. For example, you can enter your current weight and target weight, and the app will calculate a daily calorie allowance to meet that goal. If you type in the food you eat throughout the day, the app will compute the calories you've consumed, calculate the calories you have burned, and tell you how many calories you have left in your daily allowance.

Some brands of trackers, including Fitbit and Withings, can be synchronized with "smart scales" that wirelessly transmit your weight to the app. The scales are sold separately for around $100.

Data sharing

If you want more than electronic feedback on your progress, you can share your data with your friends, family, and physicians. If you'd like a benchmark, you can find an online community of people who wear the trackers and are your age or have similar fitness goals, and match your activity to theirs. "I know quite a few physicians who compare their own activity with that of their colleagues around the country," Dr. Elson says.

The graphs and charts from the apps may come in handy if your health care provider has suggested you keep a log of your activity, diet, or sleep. Your doctor might appreciate having the information available in a compact format.

How well do they work?

According to a small study of six trackers reported in February 2015 in The Journal of the American Medical Association, all were fairly accurate in recording steps. Yet scores of additional brands and models are available. If you're thinking of investing in one, check out the Wellocracy website (www.wellocracy.com), a joint project of two Harvard affiliates—Brigham and Women's Hospital and Massachusetts General Hospital. It offers an up-to-date comparison of the features and prices of many of these devices.

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