Watch metric
HRV (Heart Rate Variability)
HRV (Heart Rate Variability) Definition
The tiny variation in time between consecutive heartbeats. More variation generally points to a more rested, less stressed body, and it is usually measured overnight.
Lots of watches will take some time to assess your baseline HRV and then notify you that you're 'unbalanced' if it falls outside that range for a few days.
HRV is a relatively good proxy for how well your nervous system is doing. A higher HRV generally (not always) means that your central nervous system (CNS) is less stressed.
If you drink alcohol, do a really hard workout or have a hard day, you'll notice your HRV generally dip. Resting and feeling relaxed generally raises it.
HRV is not comparable between people either, different people have different nervous systems to two people's figures cannot be compared.
You also cannot 'train' your HRV like some new apps promote. It's a measurement based on the gaps between your heart beats and we already know what impacts it.
When it helps
As a recovery trend over weeks, once you have a personal baseline.
When it doesn't
As a daily yes or no on whether to run. One poor night is not a reason to skip.
The common myth
That you can train your HRV. You can't, it's scummy marketing by dodgy apps. HRV