Your heart doesn’t beat at a uniform clip; different amounts of time pass between consecutive heartbeats. Heart rate variability is a measurement of this time variation between heartbeats in milliseconds.
To understand why this nitty-gritty health metric is important, you need to know about the autonomic nervous system (ANS). If your HRV is an orchestra, your ANS is its conductor.
The ANS comprises your parasympathetic (rest-and-digest) and sympathetic (fight-or-flight) networks. These networks constantly send signals that dictate how your body uses resources. When you are fighting off a cold, for example, the sympathetic nervous system overrides the parasympathetic; it sends a loud and clear signal that now is not the time to relax.
The more attuned your HRV is to these signals, the higher it will be. If you have a high HRV, that means that the signals from the parasympathetic and sympathetic systems are well balanced, and your body is responding to them quickly. If your HRV is lower, that’s a sign that one system is overriding the other (almost always the sympathetic) and calling the shots.
“HRV can be an indicator that our bodies are under stress or responding to illness,” says Aravind Natarajan, Ph.D., a physicist and staff research scientist at Fitbit.
Your HRV is bound to dip when you get sick, have a poor night of sleep, or finish a tough workout. But over time, you want your general HRV trends to be high. Having a consistently low HRV indicates that your body is under chronic stress, and it could put you at risk for heart attack and stroke.
When used properly, HRV can be a valuable biofeedback metric that provides clues on how to deepen sleep, optimize athletic performance, improve mental health, and more.
Some people naturally have a higher HRV than others. However, there are plenty of ways that you can improve upon your baseline through lifestyle change.
