HRV (Heart Rate Variability)

The best single readiness metric you can track daily.

What it is

HRV measures the variation in time between consecutive heartbeats. Higher variability (counterintuitively) means your autonomic nervous system is more adaptable and resilient.

Why it matters

HRV captures how well you are recovering — from training, illness, stress, or treatment. A downward trend before you feel sick is often visible in HRV data. It is the canary in the coal mine for your physiological state.

How to test

Apple Watch (Health app), Garmin, Polar H10 chest strap (most accurate), or Oura ring. Measure at the same time each morning before getting out of bed.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

Highly individual. Establish your personal baseline over 4–6 weeks. Trend matters more than absolute number. Most adults: 40–80ms RMSSD.

How often

Daily. Look at 7-day rolling average rather than single readings.