What affects your HRV, and how to find out what affects yours

What HRV is

Your heartbeat isn’t perfectly regular. The gaps between beats vary slightly, and HRV summarises how much. There are several ways to calculate it, so a number from one device or app can’t be compared directly with a number from another.

Why your numbers can’t be compared with other people’s

Published reviews of HRV research stress that typical values depend on age, sex and, importantly, how and for how long it was measured. A 5-minute reading, an overnight average and a 24-hour value are not interchangeable. This is why “is my HRV good?” has no useful answer without knowing what is normal for you, measured the same way.

Things commonly linked to changes

Researchers and wearable makers commonly point to a handful of factors. None of these is a rule, and their effects differ between people:

• Sleep: how long and how well you slept.
• Alcohol, especially in the evening.
• Training load: hard sessions, and how recovered you were going in.
• Illness or a developing infection.
• Stress and a busy or disrupted day.
• The time of day and conditions of the measurement itself.

How to learn what moves yours

The reliable way to find out is to look at your own data over several weeks, with a note of what you did on each day. Because many of these factors travel together (a stressful day can mean a late meal, a drink and a poor night), simply noticing that two things go together can mislead. Tools that adjust for other factors and for chance, as The Gap does, are better placed to tell what seems to matter for you.

A low reading on its own is not a diagnosis. If your HRV or any other reading worries you, or changes sharply for no reason you can find, talk to a doctor.