Millions of people wake up to a heart rate variability score on their Fitbit, Apple Watch, WHOOP or Garmin. Few know what the number means, and even fewer know how it should shift as they age.

Wearables measure several aspects of health, and heart rate variability might be one of those. It may be surprising when your device informs you that your heart rate variability is high or low, but ...

Did you know there’s a number that might let you know how stressed you are, whether you have a cold coming on and how to get into the zone if you’re about to present at a big meeting? You can find ...