Do Fitness Trackers Accurately Count Calories?

Do Fitness Trackers Accurately Count Calories?

Title: Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort

Author: Shcherbina et al

Journal: Journal of Personalized Medicine (2017, May)


The popularity of smartwatches and fitness trackers has surged over the last several years. According to, there were 325 million connected wearable devices worldwide in 2015 and that number was expected to grow in 2016.

These devices are marketed as a weight loss tool for those looking to make life changes, and more data for those looking to fine tune their healthy lifestyle. Although they vary from product to product, different activity trackers can track distance walked or run, calorie consumption (or energy expenditure), heart rate and quality of sleep.

Their ability to track calories burned has attracted the attention of many folks who are obese or overweight looking to lose weight. The benefits of weight loss are clear and included decreased risk of heart attack, stroke, diabetes, cancer, and death among many others. In fact, healthcare systems have been trialing these products around the country as part of a broader weight loss strategy for the prevention and treatment of disease.

How well these commercial fitness trackers count calories is not clear. The authors of this study sought to collect data  from laboratory testing of some of the more popular commercial devices in diverse conditions and then presented the data and recommendations.


They tested the follow fitness trackers: Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, MIO Alpha 2, PulseOn and Samsung Gear S2.

They had 60 participants who performed two rounds of 40 tests for a total of 80 on the various products.

To stress them physically, they were placed on either a treadmill or a stationary bicycle where they tracked heart rate and energy expenditure according the the devices.

They measured age, body mass, height, BMI, skin tone, wrist circumference and VO2 max.


The devices were the most accurate during cycling and the least accurate while walking. Device error was higher for males, greater body mass index, darker skin tone, and walking.

Six of the seven devices achieved a median error for HR below 5% during cycling.

No device was able to achieve an energy expenditure error below 20%.

The Apple Watch was the most accurate for both heart rate and energy expenditure while the Samsung Gear S2 was the least accurate.


Most of the wrist worn fitness trackers estimated heart rate with an accuracy of >95%, especially while cycling.

Regarding energy expenditure, that estimate was much less accurate. This suggests individuals and professionals should use caution when using the energy expenditure or calorie counts produced by the devices to make decisions.

Also worth noting is that a recent publication in JAMA found that 24 months of using wearable technology did not lead to weight loss and surprisingly, those who did not use the fitness trackers lost more weight.

Original Article

Shcherbina, A., Mattsson, C. M., & Waggott, D. (2016). Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. doi:10.1101/094862


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