What Is Heart Rate Variability (HRV)?

Heart Rate Variability (HRV) measures the variation in time between consecutive heartbeats. Contrary to common belief, a higher HRV is generally better — it reflects your autonomic nervous system's ability to adapt and regulate.

Why Does HRV Matter?

Your heart doesn't beat like a metronome. A healthy heart has subtle time differences between each beat. This variability is governed by the autonomic nervous system:

• Sympathetic branch (fight-or-flight) speeds up your heart, reducing variability
• Parasympathetic branch (rest-and-digest) slows your heart, increasing variability

During sleep, the parasympathetic branch dominates. A higher sleep HRV suggests your body is recovering effectively.

What's a Normal Range?

HRV varies significantly by age, sex, and individual fitness:

• Age 20–30: average 40–80 ms
• Age 30–40: average 30–60 ms
• Age 40–50: average 25–50 ms
• Age 50+: average 20–40 ms

This is exactly why Mellows uses a personal baseline — your HRV should only be compared to yourself.

What Affects HRV?

• Increases HRV: Regular exercise, adequate sleep, meditation, balanced nutrition
• Decreases HRV: Chronic stress, alcohol, sleep deprivation, overtraining, illness

Reading HRV in Mellows

Mellows tracks your HRV throughout the night and compares it against your personal baseline. When HRV drops significantly below your normal range, it may signal that your body is under extra stress — a cue to prioritize recovery.