It’s when the first metric increases or decreases in sync with the second, but with a lag between the second and first metrics. The lag time can amount to one day, one week, or one month, depending on which chart view you’re using.

Here’s what it looks like:

This means that if you cover more distance walking and running this month, your average heart rate will be higher next month in 70% of cases.

And if your walk/run less this month, your average heart rate will be lower next month.

If you see a correlation like this, it might mean that you’re overdoing it in terms of how much you walk/run, and your heart rate tends to spike because your body doesn’t get a chance to fully recover. This may be a sign to rethink your workout routine.