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Reference
Protocol Glossary
Science-backed definitions for every term in your health data: plain English and the mechanism behind it.
Biometrics
Heart Rate Variability (HRV)
Your nervous system's daily readiness signal
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Cortisol Awakening Response (CAR)
The first hormonal signal that sets your day
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VO2 Max
The strongest single predictor of long-term health and longevity
→ Read definitionBiometrics
Resting Heart Rate (RHR)
How hard your heart works when it doesn't have to
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RMSSD (Root Mean Square of Successive Differences)
The beat-to-beat calculation that powers your HRV score
→ Read definitionBiometrics
SDNN (Standard Deviation of NN Intervals)
The HRV metric Apple Watch uses, and why it reads higher than Oura
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Vagal Tone
The strength of your parasympathetic recovery signal
→ Read definitionBiometrics
SpO2 (Blood Oxygen Saturation)
The percentage of your red blood cells carrying oxygen
→ Read definitionBiometrics
Respiratory Rate
Breaths per minute: your body's quiet early warning signal
→ Read definitionMore terms added regularly. Check back for new entries across all categories.
