Accuracy of Optical Heart Rate Sensing Technology in Wearable Fitness Trackers for Young and Older Adults: Validation and Comparison Study.

Chao-Ching Yang,Hsueh-Wen Chow

doi:10.2196/14707

Abstract

BackgroundWearable fitness trackers are devices that can record and enhance physical activity among users. Recently, photoplethysmography (PPG) devices that use optical heart rate sensors to detect heart rate in real time have become popular and help in monitoring and controlling exercise intensity. Although the benefits of using optical heart rate monitors have been highlighted through studies, the accuracy of the readouts these commercial devices generate has not been widely assessed for different age groups, especially for the East Asian population with Fitzpatrick skin type III or IV.ObjectiveThis study aimed to examine the accuracy of 2 wearable fitness trackers with PPG to monitor heart rate in real time during moderate exercise in young and older adults.MethodsA total of 20 young adults and 20 older adults were recruited for this study. All participants were asked to undergo a series of sedentary and moderate physical activities using indoor aerobic exercise equipment. In this study, the Polar H7 chest-strapped heart rate monitor was used as the criterion measure in 2 fitness trackers, namely Xiaomi Mi Band 2 and Garmin Vivosmart HR+. The real-time, second-by-second heart rate data obtained from both devices were recorded using the broadcast heart rate mode. To critically analyze the results, multiple statistical parameters including the mean absolute percentage error (MAPE), Lin concordance correlation coefficient (CCC), intraclass correlation coefficient, the Pearson product moment correlation coefficient, and the Bland-Altman coefficient were determined to examine the performances of the devices.ResultsBoth test devices exhibited acceptable overall accuracy as heart rate sensors based on several statistical tests. Notably, the MAPE values were below 10% (the designated threshold) in both devices (GarminYoung=3.77%; GarminSenior=4.73%; XiaomiYoung=7.69%; and XiaomiSenior=6.04%). The scores for reliability test of CCC for Garmin were 0.92 (Young) and 0.80 (Senior), whereas those for Xiaomi were 0.76 (Young) and 0.73 (Senior). However, the results obtained using the Bland-Altman analysis indicated that both test optical devices underestimated the average heart rate. More importantly, the study documented some unexpected outlier readings reported by these devices when used on certain participants.ConclusionsThe study reveals that commonly used optical heart rate sensors, such as the ones used herein, generally produce accurate heart rate readings irrespective of the age of the user. However, users should avoid relying entirely on these readings to indicate exercise intensities, as these devices have a tendency to produce erroneous, extreme readings, which might misinterpret the real-time exercise intensity. Future studies should therefore emphasize the occurrence rate of such errors, as this will likely benefit the development of improved models of heart rate sensors.

Highlights

Growing Popularity and Functions of Wearable Fitness TrackersWearable fitness trackers have gained popularity worldwide, and their annual sales continue to grow [1,2]
Whereas the Xiaomi device generally achieved mean absolute percentage error (MAPE) values of less than 10%, it did not do so during cycling and elliptical phases (Table 1), suggesting that the reliability of the Xiaomi device was likely influenced by the types of activities performed
The MAPE values achieved by the Xiaomi device were, on average, higher than those produced by the Garmin device, indicating that the Xiaomi product was overall less reliable than the Garmin one

Summary

Introduction

Growing Popularity and Functions of Wearable Fitness TrackersWearable fitness trackers have gained popularity worldwide, and their annual sales continue to grow [1,2]. Earlier versions of fitness trackers, equipped with triaxial accelerometers and a gyroscope, could sense motions made by the users, monitor their activity metrics, and provide estimated information such as walking and running in terms of steps or distance, energy expenditure, sedentary time, sleep patterns, and activity routes (with GPS function). Most of these fitness trackers were placed on the wrist. The benefits of using optical heart rate monitors have been highlighted through studies, the accuracy of the readouts these commercial devices generate has not been widely assessed for different age groups, especially for the East Asian population with Fitzpatrick skin type III or IV

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Discussion

Conclusion