The researchers summarized the data collected into a simple table that assessed the accuracy, variability and reliability of each device.
It turns out that all devices are pretty bad at tracking calories in almost all activities. Not only that, but the average deviation from actual daily spending is unpredictable and highly variable, rendering the watch useless for tracking calories. This is because progress cannot be reliably tracked even if the absolute value is biased. Wearables are even more inconsistent for those with below-average and above-average energy expenditures. The study also appears to be consistent with previous studies that have attempted to assess the same abilities but using different wrist-worn devices.
The good news is that the Apple Watch Series 6 is pretty solid at tracking heart rate data across all exercise conditions, and the accuracy of the Polar Vantage V and Fitbit Sense wearables fluctuates based on exercise. Step counts also appeared to be relatively consistent across all devices involved in the study.
Despite its limitations, such as the small sample size of devices and individuals, this study appears to be consistent with previous research showing that smartwatches and wrist-worn fitness trackers on the market do not contribute to your daily energy Consumption provides a reliable measure. Furthermore, their results are inherently very unpredictable.
Still, heart rate tracking and step counting are generally fairly useful and reliable features. In fact, some studies suggest that smart wearables alone may introduce a positive impact on a person’s fitness life. People who use smart wearables tend to increase their overall activity and step count.