Fitness trackers accurately record Heart Rate, but are wrong at body's calories, according to a new study . So if you use them as a tracker for what to eat, it will probably be misleading.
Researchers at the Stanford Medical School, California, tested seven brands (Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn, Samsung Gear S2), with 60 men and women as volunteers, who did a "treadmill" and a static exercise bike. As the tests showed, some devices proved to be more accurate than others, but no device did manage to correctly measure energy consumption (calorie burning) during exercise.
Even the most accurate device (Fitbit Surge) had a 27.4% deviation from the correct value, while the less accurate (PulseOn) showed a deflection of almost 93% of the actual calories burned, as indicated by indirect calorimetry analyzes (oxygen measurements and carbon dioxide in breathing), which scientists did to volunteers, and six of the seven devices studied measured the heart rate with less than 5% error [2, 3].
Researchers have said that fitness trackers do not have the same precision specifications as the medical devices, and it is inappropriate to guide people or doctors in their decisions, especially when it comes to the nutrition and you have a chronic health problem. Researchers are not sure why fitness trackers fall out of the way of eating calories. Each device uses its own algorithm to calculate energy expenditure, but it is a trade secret of the manufacturer.