Heart Rate Variability and Stress Level - Garmin Fenix 6 Solar manual
An Alternative Reference Index to Monitor Fatigue – Heart Rate Variability ( HRV) - Garmin Blog
HRV Analysis | Garmin Connect IQ
✓ [Updated] Welltory: EKG Stress Test & HRV Heart Rate Monitor PC / Android App (Mod) Download (2022)
An interesting article about the measurement Garmin devices use for the ' Stress' and 'Body Battery' features - "The stress test: What heart rate variability can tell you about your mental health" :
How to measure HRV on a Garmin without a chest strap