Florida International University said on Monday that a new study found smartwatches may not accurately calculate calories burned during exercise, potentially negatively affecting the weight-loss process. In the study, 58 Hispanic adults wore an Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5 and Garmin Forerunner 955 while performing 10-minute moderate- and high-intensity workouts on an exercise bike. The data was compared with the COSMED K5 metabolic analysis device, which measures breathing, oxygen consumption and energy expenditure. Apple produced the most accurate results, while Garmin and Samsung were the brands that overestimated calories the most. Fitbit either failed to provide data for some measurements or reported very low, implausible values; because a significant portion of this data was excluded from the evaluation, no definitive accuracy conclusion could be reached. The errors were found to become more pronounced in people with higher body fat percentages, who may have a greater need to track calories. Researcher Jason Kostrna said the test data used in the algorithms may have played a role. It was reported that the watches could still be useful for health tracking and that strength training would be examined in the next stage.
Why it matters
The findings show that calorie data from smartwatches may not be a measurement that can be relied on alone during the weight-loss process; this limitation becomes more important, particularly for users with higher body fat percentages. Differences between brands mean that the device used for the same exercise could affect a person’s assessment of their daily energy balance and progress. However, the exclusion of some of the data on Fitbit from the evaluation prevents a definitive accuracy comparison from being made for this brand. The fact that the study was based solely on moderate- and high-intensity exercise on a stationary bike also leaves open whether the results apply to strength training. The test data used to develop the algorithms emerges as one of the reasons for the differences in the measurements.