Heart rate variability (or HRV) is the latest hot health measurement. It’s being used by athletes to optimize their training, and as a predictor of health—including in a number of studies on COVID-19. Your Apple Watch tracks it automatically. Here’s what you need to know about it, and why it matters.
What Is HRV?
Heart rate variability is a measure of how much the time between two heartbeats varies from beat to beat. It’s controlled by your autonomic nervous system (ANS), which is responsible for breathing, digestion, and other unconscious bodily functions.
The ANS has two big subcomponents: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The SNS reacts to stress and controls your body’s “fight-or-flight” responses. The PNS, on the other hand, controls your body’s “feed-and-breed” and “rest-and-digest” responses. It’s what ticks over when everything is normal.
HRV is a way of measuring ANS activity. When the SNS is active—in other words, when you haven’t slept too well, are fighting with your partner, or are otherwise a bit stressed—the variation between heartbeats is lower than when the PNS is active. If you’re relaxed and chilled out, your heart rate just bounces around a bit more.
Of course, stress isn’t the only thing that affects HRV. Age, gender, genetics, hydration, exercise, illness, and many more things influence it. Stress is just one of the big factors that can do it.
