When HR was below 100bpm and patients were in sinus rhythm (part of the normal range of cardiovascular functioning) the Apple Watch was only 1.0 beat off the true HR, the Polar A360 3.8 beats off and the Garmin Vivíosmart 9.8 beats off. Both Fitbit devices we over 10 beats off. All the devices were less accurate when the patients was in AF and when true HR was over 100 bmp.
In a 2018 conference paper 4 healthy participants rotated wearing 4 different Vivíosmart 3 devices as they walked at various speeds on a treadmill. The data collected were compared to a baseline ECG device and Mean Absolute Percentage Error (MAPE) and IntraClass Correlations (ICC) were calculated. A MAPE of 10% of above was considered unacceptable. Their results showed that each individual device performed differently across different participants.
The table and figure below show the differences across individuals with different devices (red, blue, green and black