Is it Stress O’Clock?: Comparing Cardiac Data from Industry-Leading Smartwatches against Subjective Workload Measures

Health information like heart rate (HR) and electrocardiogram (ECG) patterns are available to the public on smartwatches; however, there may be a disconnect between these health measures and how users subjectively experience feelings of stress. This study examines the health detection features of two leading smartwatches in the industry, the Apple Watch Series 6 and Fitbit Sense, to determine if these devices may be used to accurately measure stress. Participants engaged in a multi-tasking program (MATB-II) that varied in cognitive workload demand while wearing smartwatches measuring cardiac data. Subjective workload responses resulted in significant differences between low and high workload conditions, indicating an increase in stress. However, both smartwatches were unable to detect significant differences in stress responses between low and high workload conditions. Overall, these results indicate that smartwatch HR and ECGs may not reflect internal feelings of stress and are sensitive to variability in measurement.