One feature a number of fitness trackers offer is a metric called “heart rate variability,” or HRV, which is the interval of time between each heartbeat. But given that we tend to think of our hearts beating at a steady and predictable pace, the fact that the interval between each beat varies can be a hard concept to grasp.
However, since HRV is responsive to stress—whether it’s anxiety, sleep deprivation, overtraining, or any of many other physical and mental stressors—keeping an eye on your HRV can be a way to gauge whether your overall lifestyle needs a change. For example, a lot of professional and endurance athletes will keep an eye on their HRV as a way of gauging how their overall stress levels may be affecting their performance.
“HRV is a very good measure of the efficiency and performance of your cardiovascular system,” said John P. Higgins, MD, a sports cardiologist with McGovern Medical School at UTHealth Houston. “A high HRV means your heart is performing like a Ferrari, which can go from 0 to 60 in 2.7 seconds.”
Heart rate variability is controlled by our autonomic nervous system
Our HRV is controlled by our autonomic nervous system (ANS), which controls our fight-or-flight instinct, as well as our relaxation response. Depending on what’s going on in our lives, whether it’s a bad night of sleep, a stressful situation at work, or any exciting developments, this will cause our brain to either stimulate or relax different bodily functions, which includes heart rate, breathing rate, blood pressure, and digestion. This also includes your heart rate variability, which will either drop when your stress levels are high, or go up when your life has a healthy balance.
There are a lot of factors that affect your HRV, including how much sleep you’re getting, how nutritious your diet is, whether you’re getting the exercise your body needs, if you’re over-training, and your general stress levels. A low HRV has also been linked to worsening anxiety and depression and an increased risk for cardiovascular disease.
Heart rate variability can change as a result of lifestyle
The good news is when it comes to your own HRV, these values can shift depending on what’s going on in your life. As Higgins notes, our HRV generally varies within a stable range over a period of weeks to about a month, and can change in a positive direction fairly quickly. “Exercising is the best way to improve heart rate variability and it can pay off in as little as two months,” Higgins said.
Keeping an eye on your HRV can be a good way of assessing whether you need to reduce the level of stress in your life, and whether your stress reduction methods are working. Given the enormous levels of stress we’ve all been under these past 18 months, reducing our stress is probably an issue we are all thinking about.
Knowing your heart rate variability can help avoid overtraining
For people who are training for something, such as a marathon or triathlon, keeping an eye on your HRV can also help you determine whether you’re overtraining. As Higgins explains, after a hard workout, your HRV will be lower. A sign that you’ve recovered from this workout is when your HRV has returned to normal, which tells you that your body is ready to exercise again.
In this way, keeping an eye on your HRV can help you understand what level of training is best for your body. “A high HRV is associated with improved body system functioning,” Higgins said. If your body is functioning well, then that usually translates to an improved athletic performance.