Your heart does not beat like a metronome. Even at rest, the interval between heartbeats varies — sometimes by tens of milliseconds. This variation, called heart rate variability (HRV), is not a sign of dysfunction. It is a sign of health. Higher HRV indicates a nervous system that is flexible, adaptive, and resilient. Lower HRV indicates a system that is rigid, stressed, and vulnerable.
What HRV Tells You
HRV reflects the balance between sympathetic (activating) and parasympathetic (calming) nervous system activity. When the parasympathetic system is dominant — indicating safety and recovery — the vagus nerve modulates heart rate on a beat-by-beat basis, creating higher variability. When the sympathetic system is dominant — indicating stress — the heart rate becomes more rigid and metronomic.
Research has established HRV as a predictor of outcomes across an remarkably wide range of domains: cardiovascular health, immune function, cognitive performance, emotional regulation, athletic recovery, and even mortality risk. A 2018 meta-analysis found that low HRV was associated with a 32-45% increased risk of cardiovascular events.
Measuring and Training HRV
Modern wearable devices (Oura Ring, WHOOP, Apple Watch, Garmin) make HRV tracking accessible. The key metric for most people is resting HRV, measured first thing in the morning before getting out of bed. Trends over weeks and months are more meaningful than any single reading.
HRV biofeedback training involves breathing at your resonance frequency — typically around 5-7 breaths per minute — while monitoring HRV in real time. This practice has been shown to increase resting HRV, reduce anxiety, improve athletic performance, and enhance emotional regulation. Studies show measurable improvements in as little as 4-6 weeks of daily 10-minute sessions.
Lifestyle Factors That Affect HRV
Sleep is the single strongest lifestyle determinant of HRV — even one night of poor sleep can reduce HRV by 10-20%. Alcohol, even in moderate amounts, suppresses HRV for 24-48 hours. Regular aerobic exercise increases resting HRV over time. Chronic stress, overtraining, and illness all reduce HRV.
HRV serves as an integrative biomarker that reflects the health of multiple pillars simultaneously. A declining HRV trend might indicate poor sleep, gut inflammation, hormonal imbalance, or chronic stress — often before symptoms become apparent. This makes it one of the most valuable early warning systems available.