Fitness trackers and smart watches are widely popular wearable devices that measure several types of health metrics, including step count, calories burned, sleep quality, Vo2 max and heart rate.
As a marathon runner, I like to monitor several of these health metrics on my Garmin Forerunner 255, to make sure that I’m recovering from workouts well and that I’m not overdoing it on days where I may need more recovery.
But one metric that may be worth paying attention to is your heart rate variability (HRV), which measures the variation in time between heartbeats. (Of course, on a watch it only provides an estimate.)
While some cardiologists say it’s not an important metric when it comes to cardiovascular health or fitness, others say it just might — and can also lend a snapshot into another part of your health: how well your nervous system can regulate after stressful periods.
[READ: How to Assess Your Heart Health]
What Is Heart Rate Variability (HRV)?
HRV refers to the time variation between consecutive heartbeats.
Everyone’s resting heart rate is different. The average resting heart rate for adults ranges between 60 and 100 beats per minute. But endurance athletes may have resting heart rates as low as 30 to 40 beats per minute.
“While your heart may beat at 60 beats per minute, for example, those beats are not perfectly spaced apart, and the subtle changes in timing are what HRV measures,” says Mark Kovacs, a human performance physiologist and longevity expert.
HRV is a reflection of your autonomic nervous system, your body’s fight-or-flight response, and can therefore indicate how well your body responds and recovers from stress, including the physical demands of a workout and the mental demands from a tough workday.
Your autonomic nervous system comprises the sympathetic and parasympathetic nervous systems:
— Sympathetic nervous system. This is your body’s fight-or-flight mode. It activates when you’re scared, stressed or anxious, and it triggers the release of adrenaline, a hormone that speeds up your heart rate and raises your blood pressure to prepare you to respond to the perceived threat quickly.
— Parasympathetic nervous system. This is your body’s rest-and-digest mode. It’s what helps you calm down and lower your blood pressure and heart rate after a stressful moment.
“A higher HRV generally suggests your body is more adaptable and resilient to stress, while a lower HRV can indicate fatigue, illness or accumulated stress,” Kovacs says.
[READ: How to Identify High Cortisol Symptoms and Lower Your Cortisol Levels]
Normal HRV Ranges
Just as average heart rate varies among people, so does HRV.
“The range of an individual’s average HRV is wide: from 20 to over 120 milliseconds,” says Alexa Lobato, the lead performance physiologist at Human Powered Health in Scottsdale, Arizona. “Knowing your average HRV is important to understand if or when your body is reacting positively or negatively to an aspect of your life. Deviations from your average value could indicate that something is off.”
Factors that affect HRV include:
— Age. Much like max heart rate, HRV decreases with age. A normal value for someone over age 50 is going to be less than someone at age 20 or 30. It’s not uncommon to see HRV dip into the mid-20s after age 50.
— Sex. Men tend to have higher HRV than women.
— Fitness levels. Those who are more physically fit (especially endurance athletes) often have higher HRV trends due to better cardiovascular efficiency, compared to sedentary people. Sedentary young adults may have an HRV of around 40 milliseconds, whereas a well-conditioned athlete may have an HRV that surpasses 100 milliseconds.
— Stress. Chronic stress can affect your nervous system; specifically, it can make you feel stuck in fight-or-flight mode, which can affect HRV.
— Sleep quality. Not sleeping well can increase stress levels, which can negatively affect HRV. The reverse is also true: High-quality sleep can reduce stress levels and balance HRV levels.
— Time of day. For the most accurate HRV reading, it’s best to measure in the morning, as daily activities and stressors can suppress the results.
— Caffeine intake. Consuming caffeine (such as a cup of coffee) before measuring your HRV can affect your reading. Studies suggest a quick hit of caffeine can trigger your fight-or-flight response and subsequently lower your HRV score.
[Read: HIIT vs. Cardio for Weight Loss.]
How to Track HRV
If you are tracking your HRV at home, it’s important you know when and how to check it so you get the most accurate estimate possible.
“The most reliable times are during deep sleep or first thing in the morning before you’ve had caffeine, eaten or engaged in activity,” Kovacs says.
To track HRV in your sleep, you either need to wear your watch or ring to sleep or lie on a sleep-monitoring mat. If you’re measuring your HRV while awake, lie flat on your back and measure it for five minutes. Try to stay as relaxed as possible so that the data are collected as you’re in a rested state.
“If people are tracking their heart rate variability, they should pay closer attention to the trend more than the absolute value,” says Dr. Sean Swearingen, a cardiologist and director of sports and exercise cardiology at Rush University System for Health in Chicago.
Lobato concurs: “I look at the average HRV throughout my entire sleep duration. Having the range and average gives me an overall sense of how my body is feeling and functioning.”
What Your HRV Can Tell You About Your Health
Here’s what HRV may tell you about your emotional and physical well-being:
Stress levels
If your sympathetic nervous system is constantly on high alert, it can affect your HRV — and overall health.
“Lower HRV can signal that your body is under more physiological stress — whether from poor sleep, illness, overtraining or mental stress,” Kovacs says. “It’s an early warning sign to slow down and recover.”
Fitness or recovery
When you think of fitness metrics, as resting heart rate lowers, that can indicate you’re adapting well to exercise and have strong cardiovascular fitness. But it’s different for HRV.
“As a person adapts to exercise, we often see an increase in their HRV,” says Dr. Amir Mahajer, an osteopath double board-certified in physical medicine, rehabilitation and sports medicine.
More specifically, this increase suggests your nervous system is spending more time in rest-and-digest mode, versus working overtime in fight-or-flight.
“HRV is widely used by athletes to gauge readiness,” Kovacs adds. “A sudden drop in HRV can indicate you may need more recovery before your next hard session.”
Long-term health risks
HRV has been studied since the 1960s, but it’s still not clear whether it can reveal larger health problems.
“A reduced heart rate variability has been associated with increased cardiac events in both patients with heart conditions and the general population,” says Dr. Blair Suter, a cardiologist at the Ohio State University Wexner Medical Center.
Research from the American Diabetes Association also shows a strong association between lower HRV and prediabetes and Type 2 diabetes, though again, researchers aren’t yet sure why. However, the findings from this study do suggest that problems with the heart’s autonomic regulation may begin as early as the prediabetes stage.
How to Improve Your HRV Naturally
Improving your HRV may take time, but you can try to do so by making certain lifestyle modifications. These include:
— Exercise regularly
— Eat a balanced diet
— Adopt good sleep hygiene habits that help improve sleep
— Engage in stress management practices (such as meditation or breathwork)
— Manage occupational and environmental stressors
— Practice mindfulness and gratitude
After making some of these changes, you may notice positive trends in your HRV.
“If I go to bed at the same time consistently, my HRV trends up,” Lobato says. “If I drink coffee too late in the day, consume alcohol or have a big day at work the upcoming day, my HRV trends down.”
When to Talk to a Doctor About HRV
Try not to let the number on your fitness app scare you. Remember, wearables can only provide estimates at best. However, if you’re concerned about your recent HRV trends, consider making an appointment with your health care provider.
“Although it is reasonable to wear devices that collect this information, it’s best to follow up with a physician if you are concerned about a specific metric that might seem abnormal,” Swearingen says.
Bottom Line
There’s still a lot we don’t know about HRV, including whether consistently low scores can predict chronic disease. However, experts say HRV can offer helpful insight into how well your body is recovering from workouts or stressful periods, which is valuable information for supporting your overall well-being. You can track HRV with fitness wearables, but to get the most accurate reading, an electrocardiogram (ECG) is best. When in doubt, talk to your health care provider.
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Heart Rate Variability: What It Is, How to Track It and What It Means for Your Health originally appeared on usnews.com
