A comprehensive accuracy assessment of Samsung smartwatch heart rate and heart rate variability

Abstract

Background Photoplethysmography (PPG) is a low-cost and easy-to-implement method to measure vital signs, including heart rate (HR) and pulse rate variability (PRV) which widely used as a substitute of heart rate variability (HRV). The method is used in various wearable devices. For example, Samsung smartwatches are PPG-based open-source wristbands used in remote well-being monitoring and fitness applications. However, PPG is highly susceptible to motion artifacts and environmental noise. A validation study is required to investigate the accuracy of PPG-based wearable devices in free-living conditions. Objective We evaluate the accuracy of PPG signals—collected by the Samsung Gear Sport smartwatch in free-living conditions—in terms of HR and time-domain and frequency-domain HRV parameters against a medical-grade chest electrocardiogram (ECG) monitor. Methods We conducted 24-hours monitoring using a Samsung Gear Sport smartwatch and a Shimmer3 ECG device. The monitoring included 28 participants (14 male and 14 female), where they engaged in their daily routines. We evaluated HR and HRV parameters during the sleep and awake time. The parameters extracted from the smartwatch were compared against the ECG reference. For the comparison, we employed the Pearson correlation coefficient, Bland-Altman plot, and linear regression methods. Results We found a significantly high positive correlation between the smartwatch’s and Shimmer ECG’s HR, time-domain HRV, LF, and HF and a significant moderate positive correlation between the smartwatch’s and shimmer ECG’s LF/HF during sleep time. The mean biases of HR, time-domain HRV, and LF/HF were low, while the biases of LF and HF were moderate during sleep. The regression analysis showed low error variances of HR, AVNN, and pNN50, moderate error variances of SDNN, RMSSD, LF, and HF, and high error variances of LF/HF during sleep. During the awake time, there was a significantly high positive correlation of AVNN and a moderate positive correlation of HR, while the other parameters indicated significantly low positive correlations. RMSSD and SDNN showed low mean biases, and the other parameters had moderate mean biases. In addition, AVNN had moderate error variance while the other parameters indicated high error variances. Conclusion The Samsung smartwatch provides acceptable HR, time-domain HRV, LF, and HF parameters during sleep time. In contrast, during the awake time, AVNN and HR show satisfactory accuracy, and the other HRV parameters have high errors.

Review on Wearable Technology in Sports: Concepts, Challenges and Opportunities

“…ECG is an important tool for monitoring athletes' health and performance, optimizing exercise programs, and assessing heart health [21].ECG electrodes are placed on specific locations of the torso and limbs to capture the signals generated by the cardiac depolarization and repolarization. Some commercial WT, such as smartwatches and wristbands, claim to have ECG detection capabilities, but they usually measure a single-lead ECG that is more suitable for detecting training load or cardiac disorders than for providing a comprehensive ECG analysis [22,23]. The conventional ECG acquisition is often inconvenient and intrusive, as it requires multiple electrodes and wires that may interfere with the natural movement of the athletes.…”

The use of commercial wrist-worn technology to track physiological outcomes in behavioral interventions

“…Devices from popular brands, including Apple (Apple Inc, Cupertino, California, USA), Fitbit (Fitbit Inc, San Francisco, California, USA), Samsung (Samsung Electronics Co., Ltd., Suwon, South Korea), Garmin (Garmin Ltd, Olathe, Kansas, USA), and Polar (Polar Electro, Inc., Kempele, Finland) demonstrate high agreement for HR measurements during sleep and/or rest when compared with criterion measures (i.e. ECG or chest HR monitor) [29–35]; however, as exercise intensity increases, measurement error is more likely to occur [29–32,36,37 ▪ ,39]. The extent of this relationship can be influenced by activity type, arm movement, and device [32,40].…”

“…Furthermore, accuracy may be dependent on device brand; findings from several studies suggest that Apple devices demonstrate the highest accuracy for HR assessment, even at high and maximal intensities, compared to devices from brands including Fitbit, Polar, Garmin, and Samsung[30,36,37 & ,38].Heart rate variabilityPhotoplethysmography is also used to assess HRV on wrist-worn wearables. Devices made by Apple, Garmin, Polar, Samsung, and Whoop (WHOOP, Boston, Massachusetts, USA) show moderate-to-high accuracy for assessing HRV at rest and during sleep for parameters that include the average of normal-normal (N-N) intervals (AVNN), standard deviation of N-N intervals (SDNN), root mean square of successive difference (rMSSD), percentage of successive difference of intervals between N-N interval more than 50 ms (pNN50), and the ratio of low frequency to high frequency power (LF/HF ratio)[29,34,41]. Although research focused on HRV during awake time or physical activity is limited, recent findings suggest that accuracy during specific activities or over a 24-h period is less than optimal[29,42].…”

“…Devices made by Apple, Garmin, Polar, Samsung, and Whoop (WHOOP, Boston, Massachusetts, USA) show moderate-to-high accuracy for assessing HRV at rest and during sleep for parameters that include the average of normal-normal (N-N) intervals (AVNN), standard deviation of N-N intervals (SDNN), root mean square of successive difference (rMSSD), percentage of successive difference of intervals between N-N interval more than 50 ms (pNN50), and the ratio of low frequency to high frequency power (LF/HF ratio)[29,34,41]. Although research focused on HRV during awake time or physical activity is limited, recent findings suggest that accuracy during specific activities or over a 24-h period is less than optimal[29,42]. In addition, devices differ on the type of HRV parameters assessed and data extraction methods[43], and more research is needed to validate and assess capabilities of newer models.…”

Validation of Wearable Digital Devices for Heart Rate Measurement During Exercise Test in Patients With Coronary Artery Disease

“…The exact sampling frequency of AW7 and SW4 are not made public. While the sampling frequency of the previous Samsung Watch is estimated to be between 20-25 Hz [30,31], Apple describe that their HR monitor blink hundreds of times per second to measure HR, without mentioning the precise sampling frequency [32]. Likewise, the discrepancy in www.e-arm.org each sampling frequency may be an important reason for different accuracy between devices.…”