What is SRI?
The Stress Recovery Index (SRI) is a composite score (0-100) that quantifies your autonomic nervous system balance and recovery capacity. Higher scores indicate better stress resilience and parasympathetic activity.
How is it Calculated?
SRI combines three validated Heart Rate Variability (HRV) metrics with scientifically-weighted contributions:
35%
RMSSD (Root Mean Square of Successive Differences)
Measures beat-to-beat variability. Higher values indicate greater parasympathetic (rest-and-digest) activity. Optimal: >50ms
35%
LF/HF Ratio (Low Frequency / High Frequency)
Balance between sympathetic and parasympathetic activity via frequency domain analysis. Lower ratios indicate better recovery. Optimal: 0.5-2.0
30%
HR Recovery Rate
Speed of heart rate decrease from peak to baseline. Faster recovery indicates better cardiovascular fitness and autonomic regulation.
Interpretation
75-100
Excellent Recovery
Optimal autonomic balance, strong parasympathetic activity
55-74
Good Recovery
Healthy stress response, adequate recovery capacity
35-54
Fair Recovery
Moderate stress detected, may benefit from relaxation techniques
0-34
Poor Recovery
High stress levels, prioritize recovery and rest
Scientific Validation
This index is based on well-established HRV research:
- RMSSD: Task Force of the European Society of Cardiology (1996) - Gold standard for parasympathetic activity measurement
- Frequency Domain Analysis: Validated by hundreds of peer-reviewed studies for autonomic assessment
- HR Recovery: Proven predictor of cardiovascular health and mortality risk (Cole et al., NEJM 1999)
Best Practices
- Measure SRI at consistent times (e.g., morning, before exercise)
- Allow at least 2 minutes of stable recording for accurate results
- Track trends over days/weeks rather than single measurements
- Use alongside subjective stress assessment for complete picture
- Ensure proper sensor contact for data quality >95%