Add Yahoo as a preferred source to see more of our stories on Google. If you wear a fitness tracker, you’ve likely seen a stat labeled “HRV” pop up on your screen. But what does it mean, and does it ...

If you wear a fitness tracker, you've likely seen a stat labeled "HRV" pop up on your screen. But what does it mean, and does it matter? Short for heart rate variability, HRV has become a popular ...