If youre counting on using a new fitness tracker from Jawbone, Fitbit, Microsoft or the like to help get in shape for 2015, you may want to adjust your expectations: We dont know whether or not these devices really make people more active or healthier, says Glenn Gaesser, an Arizona State University professor and Director of the Healthy Lifestyles Research Center. There really is no evidence. Still, even as some people complain of gaining unwanted weight after they started wearing a fitness tracker, many more say their gadgets are just what they need to move around moreand when you consider many Americans spend upwards of seven or eight hours a day on their tush, thats a very good thing.
1. Assume at least a 10% margin of error for calories burned.
A recent Iowa State University study found that trackers calorie-burn estimates were off by 10-15%, on average. Anyone who wants to lose weight would be wise to assume that trackers are overestimating their efforts, suggests Kristin Kirkpatrick, a registered dietitian at Cleveland Clinic. You only need to consume an extra 500 calories a day to gain a pound a week, she warns, so its smart to err on the side of caution.
2. Realize that calorie-burn estimates can be completely off. Enter them yourself.
Unless your tracker includes a built-in heart-rate monitor (like the Microsoft Band, Jawbone UP3 and Basis Peak), it will grossly underestimate how many calories you burn during many activities, including biking, weight training and yoga, because its built-in accelerometer cant as readily detect the movement. A 2013 study in Medicine & Science in Sports & Exercise found that trackers underestimate energy expenditure from cycling, for example, by up to 55%. They dont work as well on resistance exercises, says the studys co-author Ray Browning of Colorado State University. Even bands with heart rate monitors are imperfect because they dont perfectly capture your radial pulse, especially during intense exercise when you are moving your wrist a lot.