The TL;DR
Heart Rate Variability (HRV) is the variation in time (milliseconds) between consecutive heartbeats. Contrary to popular belief, a healthy heart is not a metronome. It speeds up when you inhale and slows down when you exhale. This flexibility is a sign of resilience. High HRV means your body is responsive and recovering well; low HRV means it is stressed and rigid.
Accessibility Level
Level 1 (Foundation): Requires a device with optical or electrical sensors (Oura, Whoop, Apple Watch).
The Physiology of Variation
The Tug-of-War
HRV is the result of a constant tug-of-war between the two branches of your autonomic nervous system:
- Sympathetic (“Fight or Flight”): Wants to accelerate the heart.
- Parasympathetic (“Rest and Digest”): Wants to decelerate the heart.
When you are healthy and recovered, the Parasympathetic system dominates, allowing the heart to be responsive to breathing (Respiratory Sinus Arrhythmia). This creates High Variability.
When you are stressed (sick, overtrained, sleep-deprived), the Sympathetic system takes over, pinning the pedal to the floor. The heart beats like a drum—steady and fast. This creates Low Variability.
Why It Matters for Aging
HRV naturally declines with age as our autonomic system loses flexibility. However, maintaining a “youthful” HRV is linked to reduced inflammation, better emotional regulation, and lower cardiovascular risk.
Interpreting the Numbers
HRV is highly individual. Your score depends on:
- Genetics: Some people naturally sit at 20ms, others at 100ms.
- Age: A 20-year-old averages ~60-80ms; a 60-year-old averages ~25-35ms.
- Sex: Males typically have slightly higher HRV than females.
The Golden Rule: Compare yourself to yourself. A sudden drop from your baseline is the signal that matters.
Measurement & Optimization
For protocols on how to track, interpret, and improve your HRV, see the measurement guide:
Go to: Heart Rate Monitoring Guide
References
Thayer, J. F., et al. (2010). The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. International Journal of Cardiology.
Shaffer, F., & Ginsberg, J. P. (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health.