Why Fitness Trackers Are Reliable For Heart Rate, Not Calories Burned

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The wristband tracking devices worn by millions of fitness-conscious Americans do an adequate job measuring heart rate but not  estimating energy expenditure, according to a study published earlier this year in the Journal of Personalized Medicine.

Exercise plays an important role in preventing coronary heart disease, which is responsible for one of every four deaths in the United States. The millions of people putting their faith in fitness trackers need correct information. Most are not aware that these devices, though they measure heart rate, do not account for energy expenditure — the amount of calories one needs to carry out a physical function.

Energy expenditure, or calories burned, can be challenging to record accurately because of the many different factors needed — body composition (fat to muscle mass), intensity of exercise (interval or high-intensity workouts are particularly challenging for the wrist-based HR monitors) and the user’s level of training in the specific exercise. Energy expenditure should remain a gross estimate for monitoring fitness or health goals. More specific data (total time and intensity levels) can be more helpful assessing activity levels.

Six consumer wrist-worn devices were included in the study: the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and Samsung Gear S2. The devices were tested on 60 participants who wore them while sitting, walking, running and cycling. Participants performed standardized exercises in a controlled environment while undergoing continuous ECG monitoring.

The results were not what you would hope to see in a device that could influence your health decisions. Though these devices measured heart rate with an error rate of less than 5 percent, none of the seven devices measured energy expenditure accurately. The only explanation for this is the algorithm used to assess the number of calories burned was designed for a diverse group of people.

Users of these devices should know that are reliable for heart rate measurements, but do not base the amount of calories you consume on the amount of calories the device says you’ve burned.

Hartford Healthcare Rehabilitation Network, a not-for-profit member of Hartford HealthCare, offers physical therapy, occupational therapy, speech language pathology, sports medicine and health & wellness programs.  Please call 860.696.2500 or click here for more information.

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