It's one of the most important measures of heart health, but it's rarely talked about. Here's what you need to know.
Thinking about your health means minding your heart, and you're no doubt accustomed to paying attention to measures like cholesterol, blood pressure, and triglycerides. There's one more to add to that list: heart rate variability.
“Heart rate variability is the variation in the time between each heart beat,” explains John P. Higgins, MD, MBA, a sports cardiologist at McGovern Medical School at the University of Texas Health Science Center at Houston. This is different than your heart rate, which is measured by the number of times your heart beats per minute. And unlike your heart rate, which you can calculate by counting your pulse, heart rate variability is measured at the doctor's office with an electrocardiogram (ECG or EKG) test that records the electrical activity of your heart.
Variability refers to your heart beat's ability to shift throughout the day. Your heart rate is not meant to stay the same speed at all times; it changes depending on your activity and emotions. “Think about your lowest heart rate and fastest heart rate. The difference between those is a reflection of your heart rate variability,” Dr. Higgins adds.
Need more clarity? Let's think back—way back—to our caveman ancestors. They may have had resting heart rates of, say, 60 beats per minute (bpm) when they were sitting down in those caves. But as soon as they were outside and a saber-toothed tiger came roaring by, they needed to get their heart rates up–fast–in order to move their bodies and get away quickly, explains Karol Watson, MD, PhD, director of the UCLA Barbra Streisand Women's Heart Health Program. “Our bodies were made to modulate our heart rate and blood pressure from second to second, minute to minute,” she says. That modulation is governed by the autonomic nervous system, which includes both your sympathetic nervous system (SNS, or fight-or-flight response) and parasympathetic nervous system (PNS, or your chill-out system).
The benefits of high heart rate variability
Having a high HRV means your body can efficiently change your heart rate depending on your activity. “Your heart is supposed to be able to switch gears in a heartbeat,” Dr. Watson says. Sometimes your heart may be rock steady at 60 bpm when you watch TV, and other times you need that fight or flight response needs to be activated.
"HRV is a very good measure of the efficiency and performance of your cardiovascular system,” Dr. Higgins adds. A high HRV means your heart is performing like one of those expensive cars that can go 0 to 60 in 2.7 seconds. “Studies suggest that people who have a higher HRV are actually healthier and live longer with less risk of disease,” he says. A lower HRV is associated with heart attacks, strokes, and diabetes.
Heart rate variability may also be a marker of how well your body can handle stress. With a higher HRV, Dr. Higgins says, you can perform well under duress. A low HRV, and it will be difficult to bounce back after a stressful situation.
What changes your heart rate variability?
As you age, your HRV will naturally decline. But being at an elevated risk for heart disease will also affect it. If you have a healthy heart, you don't really have to think about HRV on a daily basis, which is a relief to be sure. But disruptions to your autonomic nervous system (which also controls other unconscious behaviors like breathing in addition to your heartbeat), like an acute infection or cancer, can affect HRV. Chronic stress, high blood pressure, and high cholesterol can also impair functioning of this system, leading to problems with heart rate and blood pressure—and ultimately HRV. “Sick hearts have the same heart rate all the time, whether they're scared, running, or resting,” Dr. Watson says.
How athletes use heart rate variability
CrossFitters and other intense exercisers say that watching your heart rate variability can give you an edge and a boost in performance. After a serious workout, HRV will be lower. When your HRV returns to normal, you've fully recovered from your workout, which tells you it's safe to exercise again and helps you avoid overtraining, Dr. Higgins says. "In general, a high HRV is associated with improved body system functioning, and thus improved athletic performance," he says. He recommends looking into your HRV if your training has hit a plateau or you find that you're getting injured often.
While Dr. Watson says it's not completely clear that tailoring workouts to HRV is useful, she notes it makes sense from a physiological perspective. Though ECG monitors are the gold standard, they're not practical (or accessible) in this instance. Several fitness trackers now measure HRV, but they’re most accurate at rest. You'll need to take it up a notch if you want to use HRV in training with a heart rate monitor using either a chest strap or a finger sensor, which you can buy with a fitness tracker in conjunction with a smartphone app like iThlete or Bioforce. "They might just turn your B- or C-grade workout into an 'A'," Dr. Higgins says.
How to improve your heart rate variability
First, if there is an underlying condition that's impairing your HRV, treatment can normalize it. Talk to your doctor about other symptoms you might be experiencing. For instance, if you find that you get lightheaded often, you may have a problem within your nervous system affecting both your blood pressure and your heartbeat. “The same thing that controls HRV tends to control blood pressure variability,” Dr. Watson explains.
Your HRV won't be calculated at the doctor's office in a standard visit. If you have a suspected heart problem, your HRV may be monitored with a device that can record a continuous ECG for a day or two. Should you be diagnosed with a heart condition, though, a number of medications can improve autonomic nervous system function and heart rate variability, including beta blockers and ACE inhibitors, Dr. Watson notes, though only when appropriately diagnosed. There's no reason for a healthy individual to take these.
If you have a healthy heart, you can be confident you have a finely tuned HRV. The same factors that you hear are critical for a healthy heart apply here, too: Don't smoke, keep your cholesterol in check, and maintain a healthy weight, Dr. Watson says. It's also important to manage stress properly. Feeling keyed up is inevitable—such is life—but the goal is to build resilience and effective coping strategies to deal with it appropriately. Remember, if your body is running on high stress all the time, you won't have that critical alteration between heart rates.
Exercising is the best way to improve heart rate variability, and it can pay off in as little as two months, Dr. Higgins says, particularly in younger women and women who have recently gone through menopause. Moderate exercise for 150 minutes a week total should be your goal. Do cardio, resistance training, or HIIT workouts—whatever you love enough to do consistently.
If you like to run marathons or do triathlons, keep at it. While there's been concern in the past that high levels of exercise can adversely affect heart health, Dr. Higgins says that recent studies point to the fact that not exercising at all or enough is a bigger risk. However, over-training can negatively affect your HRV, because too much exercise stresses your system. As long as you recover appropriately (build in both rest and cross-training days throughout the week) and build up mileage or weight by 10% each week, you will be safely conditioning your heart.
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Biofeedback (where you learn to use your mind to control your body's functions) and meditation may also help improve HRV. Deep, controlled breathing taps into the parasympathetic nervous system, helping you calm down. “Breathing affects the overall stress output from your brain,” Dr. Higgins says. These exercises can help your body stimulate the PNS and quiet the SNS, for an overall healthier heart.