The Basics
Heart rate variability (HRV) measures the variation in time between consecutive heartbeats. Unlike your heart rate, which tells you how fast your heart is beating, HRV reveals how adaptable your nervous system is to changing demands.
A healthy heart doesn't beat like a metronome. Instead, there's natural variation between beats—sometimes 0.9 seconds apart, sometimes 1.1 seconds. This variation is controlled by your autonomic nervous system and reflects your body's ability to respond to stress.
Why HRV Matters
Higher HRV generally indicates better cardiovascular fitness, stress resilience, and recovery capacity. Lower HRV can signal overtraining, illness, poor sleep, or chronic stress.
Athletes use HRV to optimize training—pushing hard when recovered, backing off when depleted. But HRV isn't just for athletes. Anyone interested in understanding their body's stress response and recovery can benefit from tracking.
What Affects HRV
Many factors influence your HRV readings:
Increases HRV: Quality sleep, regular exercise, meditation, proper hydration, time in nature, strong social connections.
Decreases HRV: Poor sleep, alcohol, illness, overtraining, chronic stress, dehydration, late meals.
HRV and Age
HRV declines naturally with age, particularly between ages 20 and 40. This decline is more pronounced in men, who typically have higher HRV than women until around age 50 when the gap narrows.
Typical RMSSD ranges by age (based on 296,000+ participants): - 20s: 40-80ms average - 30s: 35-65ms average - 40s: 30-55ms average - 50s: 25-45ms average - 60+: 20-40ms average
These are averages—individual variation is significant. Compare your HRV to your own baseline rather than population norms.
How to Interpret Your Numbers
HRV is highly individual. A "good" HRV for one person might be concerning for another. What matters most is your personal baseline and trends over time.
Most apps report RMSSD (root mean square of successive differences) in milliseconds. Research suggests you need at least 5 nights of data to establish a reliable baseline. Aim for the 50th percentile in your age group as a minimum target.
Clinical note: Long-term 24-hour SDNN below 50ms is associated with increased health risks. Focus on your 7-day and 30-day trends rather than any single reading.