Your heart does not beat uniformly; different amounts of time pass between successive heartbeats. Heart rate variability is a measure of this temporal variation between heartbeats in milliseconds.
To understand why this 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 understands your parasympathetic (rest and digest) and sympathetic (fight or flight) networks. These networks are constantly sending signals that dictate how your body uses resources. For example, when fighting a cold, the sympathetic nervous system overrides the parasympathetic; sends a loud and clear signal that it is now not time to relax.
The more in tune your HRV is with these signals, the higher it will be. If you have a high HRV, it means that the signals from the parasympathetic and sympathetic systems are well balanced and your body responds quickly to them. If your HRV is lower, it’s a sign that one system is overpowering the other (almost always cute) and decisive.
“HRV can be an indicator that our bodies are under stress or reacting to illness,” he says Aravind Natarajan, Ph.D., physicist and employee researcher at Fitbit.
Your HRV will definitely drop when you get sick, you’ve had a bad night’s sleep or you’ve finished a hard workout. But over time you want your overall HRV trends to be high. A consistently low HRV indicates that your body is under chronic stress, and this could put you at risk of heart attack and stroke.
When used properly, HRV can be a valuable biofeedback metric that provides clues about how to deepen sleep, optimize athletic performance, improve mental health, and more.
Some people naturally have a higher HRV than others. However, there are many ways you can improve your bottom line by changing your lifestyle.