Do wearables like Oura, Garmin, and Apple Watch accurately measure heart rate variability (HRV) compared to direct heart monitors, such as electrocardiogram (ECG) devices, in individuals with and without known heart conditions?

Accuracy of Wearables for HRV Measurement

Consumer wearables like the Apple Watch, Oura Ring, Garmin, and Fitbit show variable accuracy for heart rate variability (HRV) measurement compared to gold-standard ECG devices, with the Apple Watch demonstrating the highest validity for heart rate measurements during both rest and activity, though significant limitations exist across all devices depending on activity type and measurement conditions. 1

Device-Specific Performance

Apple Watch

• The Apple Watch demonstrates high reliability and agreement with the Polar H7 chest strap for measuring RR intervals (the basis of HRV) during both relaxation and stress states, suggesting accurate heart data collection. 1
• Heart rate measurements from the Apple Watch Series 4 show the smallest error rates (standardized typical errors: 0.09-0.62) across different exercise intensities compared to other consumer wearables. 2
• The device provides coefficients of variation of 0.9%-4.3% for heart rate monitoring across various intensities, which is superior to competing devices. 2
• A 2025 meta-analysis confirmed mean bias of -0.12 beats/min with limits of agreement of -11.06 to 10.81 beats/min for heart rate measurements. 3

Garmin Devices

• Garmin devices show moderate accuracy but with higher error rates at certain intensities compared to Apple Watch. 2
• The Garmin Fenix 5 demonstrates standardized typical errors of 0.62-1.24 for heart rate monitoring, with coefficients of variation ranging from 2.9%-9.2%. 2
• Heart rate data from Garmin devices should be interpreted with caution due to higher error rates, particularly during variable intensity activities. 2

Oura Ring

• The Oura Ring Gen3 emerged as a suitable device for measuring cardiovascular function in community-dwelling adults based on systematic evaluation criteria. 4
• Limited specific validation data exists for HRV accuracy compared to ECG gold standards in the available literature.

Fitbit Devices

• Fitbit Versa shows the highest error rates among tested consumer wearables, with standardized typical errors of 0.47-1.94 and coefficients of variation of 4.1%-19.1% for heart rate. 2
• Fitbit devices demonstrate the poorest performance for heart rate accuracy and should not be relied upon for precise HRV measurements. 2

Critical Limitations Affecting All Wearables

Photoplethysmography (PPG) Technology Constraints

• All wrist-worn wearables using PPG technology show acceptable validity during treadmill running and walking (mean difference -0.51 bpm), but demonstrate significant underestimation during endurance sports (mean difference -7.26 bpm). 1
• PPG accuracy is substantially compromised during upper body movements and resistance exercises compared to repetitive locomotor activities. 1
• Growing evidence indicates inaccuracies in PPG green light signaling for individuals with darker skin tones compared to lighter skin tones, introducing potential measurement bias. 1

Activity-Dependent Accuracy

• Absolute error during physical activity is, on average, 30% higher than during rest across all tested wearables. 5
• Devices show reasonable accuracy at resting and prolonged elevated heart rates, but significant differences emerge between devices when responding to changes in activity. 5
• Upper body work and activities involving arm movements cause greater variability in measurement error for wrist-worn devices due to motion artifacts and variable skin contact. 1

Measurement Context Issues

• Ambient temperature may affect PPG signal quality and should be considered as a potential source of bias. 1
• Contact pressure between device and skin significantly impacts measurement accuracy, particularly during dynamic movements. 1
• Motion artifacts remain a primary source of inaccuracy, especially during activities with irregular movement patterns. 5

Comparison to Direct Heart Monitors

Chest Strap Technology

• Chest strap devices (e.g., Polar H7) are widely accepted as valid and reliable methods for heart rate monitoring in free-living conditions, with minimal measurement error compared to ECG. 1
• Chest straps provide superior accuracy for HRV measurement but present limitations for 24-hour recording over multiple days due to comfort issues. 1

ECG Gold Standard

• Direct ECG monitoring remains the reference standard for HRV measurement, as it directly traces ventricular depolarization rather than inferring heart rate from pulse wave variations. 1
• Consumer wearables using PPG cannot match the precision of ECG for beat-to-beat interval measurements necessary for accurate HRV calculation. 1

Clinical Implications and Recommendations

When Wearables Are Acceptable

• For general wellness monitoring and trend detection in healthy individuals during rest or steady-state aerobic activity, Apple Watch and Polar Vantage V provide acceptable accuracy. 2
• Population-level studies and disease surveillance applications (e.g., COVID-19 detection via HRV changes) can utilize consumer wearables when absolute precision is less critical than detecting significant deviations. 1

When Direct Monitors Are Required

• Clinical decision-making, diagnostic purposes, or research requiring precise HRV measurements necessitate ECG-based monitoring or validated chest strap devices. 1
• Patients with known cardiac conditions requiring accurate HRV assessment for risk stratification should use medical-grade devices rather than consumer wearables. 1
• Any application where measurement error could impact treatment decisions (e.g., medication titration, arrhythmia detection) requires gold-standard ECG monitoring. 1

Key Caveats

• Device model updates and algorithm changes occur rapidly, making validation studies quickly obsolete. 1
• Different validation metrics across studies make direct device comparisons challenging. 1
• No single consumer wearable currently provides accuracy equivalent to direct ECG monitoring for HRV measurement across all conditions and populations. 1
• Researchers and clinicians must consider user characteristics (age, skin tone, health status) and measurement conditions (activity type, intensity) when interpreting wearable HRV data. 3, 5