BACKGROUND
The use of wrist-worn photoplethysmography (PPG) heart rate (HR) sensors has been quickly increasing over the recent years. Wearables could be useful for researchers and individuals for their simplicity to set up and use. However, only a limited number of studies investigated the reliability and accuracy of these devices in non-laboratory controlled conditions.
OBJECTIVE
The purpose of this study was (1) to assess the accuracy and reliability of the PPG based HR sensor of the Fitbit Charge 4 (FC4) in ecological condition; (2) to quantify the potential variability caused by the nature of the activity.
METHODS
HR was simultaneously collected during various sport sessions with the FC4 and a Polar H10, as criterion. Skin tone was assessed with Fitzpatrick Scale. Intraclass correlation coefficients (ICC), Lin’s concordance correlation coefficient (CCC) and Bland-Altman test determined reliability and accuracy of the sensor.
RESULTS
HR data of 26 students aged 21.1±5.8 years on averaged were recorded during 77.47 hours of physical activity. ICCs (and CCCs) for running and orienteering running were 0.900 (0.999) and 0.801 (0.932) respectively, whereas for badminton, tennis, bike and soccer, they were 0.365 (0.778), 0.421 (0.884), 0.658 (0.971) and 0.487 (0.809), respectively. Highest biases were found for badminton and soccer, whereas smallest was found for running.
CONCLUSIONS
Researchers and individuals should not use the FC4 for measuring HR because of its LOA width and sensitivity to motion artifacts.