Summary
Systematic review found that wrist-worn and ring-based PPG devices consistently underestimate HRV compared to ECG chest straps, though they still track relative changes accurately.
Methods
Systematic review of 45 consumer wearable validation studies
Key Findings
- PPG-derived RMSSD averages 6-11% lower than ECG measurements
- Correlation with ECG remains strong (r > 0.9) for most devices
- Only 13 of 45 devices reviewed had FDA approval
- Motion artifacts remain the biggest accuracy challenge
Limitations
Studies used different protocols, making direct comparison difficult
What This Means for You
Your Whoop, Oura, or Apple Watch will likely show slightly lower HRV than a chest strap. This doesn't matter for tracking trends—just don't compare absolute values across different device types.
Source
Read the original paper in Sports Medicine ↗
Added to HRV Zone: 2025-01-07