What is HRV and what is a good score?

Heart rate variability has become a headline metric on wearables. Understanding it helps you use it well — and not worry about the wrong numbers.

What HRV is

Your heart doesn't beat like a metronome. The time between beats varies from moment to moment, and that variation is HRV. It's shaped largely by the autonomic nervous system: the "rest and digest" parasympathetic branch tends to increase HRV, while stress responses tend to decrease it.

A 2017 overview in Frontiers in Public Health describes HRV as a marker of the body's ability to adapt to changing demands. Higher resting HRV is generally associated with better cardiovascular fitness and resilience.

What's a good score?

There isn't a single target. HRV:

• Declines with age, often considerably between your 20s and 60s.
• Varies with genetics, sex and fitness.
• Differs between devices and measurement methods (such as RMSSD vs SDNN).

A number that's "low" for one person can be perfectly normal for another.

How to use HRV

Research on athletes suggests daily readings are noisy. A 2013 review recommended tracking a rolling 7-day average and watching for sustained changes relative to your baseline rather than reacting to a single morning's number.

• Stable or rising trend: you're likely adapting well.
• Falling trend for several days: consider more sleep, lighter training or less alcohol.

Ways to support HRV

Regular aerobic exercise, consistent sleep, hydration, limiting alcohol and slow breathing practices are all associated with better HRV. Learn how accurate wearables are in are sleep trackers accurate, and build a smarter plan with our recovery guide.