The Ultimate Guide to Heart Rate Variability (HRV) by Mehdi Yacoubi

The Ultimate Guide to Heart Rate Variability (HRV)
Posted on
February 17, 2022

It’s never been easier to measure and gain insight into our health and well-being. With the help of technology, we now have access to a variety of health-monitoring tools. From apps that measure your calories burned to wearable devices that track blood sugar levels, you can now have more control over your health.

One metric that popular wearable devices are currently tracking is heart rate variability (HRV), so more and more people are talking about it. This post will explain what heart rate variability is, how it works, and why it may or may not be important to you.

What Is Heart Rate Variability?

Heart rate variability, or HRV, is a measure of the variation in the time between successive heartbeats. HRV is a marker of overall health and fitness. As a general rule of thumb, the higher your HRV, the healthier your body is.

It’s different from your heart rate, which is the number of times your heart beats in a minute. If your heart rate is 70 beats per minute, it implies that your heart beats 70 times in a minute. But within this minute, there may be 0.7 seconds between two beats and 1.1 seconds between the next two beats. Heart rate variability denotes this oscillation in the interval between consecutive heartbeats.

For a long time, scientists thought that the rate and rhythm of a healthy heart remained constant. However, evidence now shows that there are small variations in the heart rhythm and rate. Heart rate variability is an indicator of a healthy nervous system.

HRV is controlled by your autonomic nervous system. The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems. Heart rate variability is due to the complex interplay between parasympathetic and sympathetic activity.

The sympathetic nervous system is activated when we need sudden bursts of physical or emotional energy, commonly referred to as the fight-or-flight response. It’s activated by stimuli like stress, anxiety, and danger. The sympathetic nervous system:

  • Increases both the breathing and heart rate so that oxygen-rich blood is pumped faster to the cells in the periphery 
  • Slows down digestion and peristalsis 
  • Constricts the blood vessels
  • Raises blood pressure
  • Dilates the pupils

In essence, the sympathetic nervous system sacrifices long-term physiological processes to address the short-term stress or danger.

Parasympathetic activity increases when the body needs to relax, like after a good meal. It controls the so-called rest-and-digest physiological response. The parasympathetic nervous system:

  • Enhances peristalsis and digestion
  • Maintains the baseline heart rate
  • Dilates blood vessels
  • Constricts the pupils
  • Conserves energy

These two systems work together to regulate vital processes, such as our heart rate, breathing rate, digestion, and blood pressure.

So what does this have to do with your HRV? When your sympathetic nervous system is revved up, your HRV reduces. Since sympathetic activity speeds up the heart, there is less variability between the beats, and that’s why HRV goes down. When the parasympathetic nervous system is in control and your heart rate slows down, your HRV goes up.

In general, if your HRV is high, then you’re more likely to be healthy and energized.

Why Should You Know Your HRV?

Heart rate variability: tired body builder with his face buried in his hand

For you to understand your body more and optimize your health, it’s important to know your heart rate variability measure. Your HRV is an indicator of your overall health and fitness level. 

High HRV is a marker of good cardiovascular health, fitness, positive emotions, low stress levels, and your ability to handle exercise and other stressors.

Low heart rate variability shows that your body is less adaptable to changing situations. HRV generally decreases with age. But low HRV can also be a sign of underlying or impending health problems, such as heart disease, chronic respiratory disease, inflammation, chronic stress, chronic pain, cancer, depression, or anxiety. 

Lower HRV values may be associated with increased cardiovascular risks, such as the risk of mortality within a few years of a myocardial infarction (or heart attack). But keep in mind, there’s still not a lot of data on HRV and mortality in normal populations.

If you’re just getting started on an exercise routine, your HRV is one of the things you’ll need to monitor. Research shows that HRV measures can be used to optimize training and athletic performance. 

After intense exercise, HRV usually decreases. With recovery, HRV rises again. HRV analysis can help you know when it's right to exercise again. Don’t use HRV in isolation though. Also assess your willingness to exercise and your resting heart rate. This way, you can avoid overtraining and maximize your athletic performance.

Other things you can track using HRV data include the quality of your sleep, nutrition, and mental health. Knowing your HRV can help you make important lifestyle changes such as adopting personalized nutrition or mindfulness practices to manage stress.

How Is Heart Rate Variability Measured?

In a clinical setting, the equipment used to measure HRV is called an electrocardiogram (also known as ECG or EKG). An electrocardiogram measures the heart’s electrical activity by using sensors connected to the chest. It’s the gold standard in HRV measurement.

An ECG provides a graphical representation of the heart’s activity. The QRS complex on an ECG represents ventricular contraction, which is responsible for each heartbeat. The time between successive heartbeats is represented by the RR interval.

Outside of a clinical setting, you can receive an HRV reading from chest sensors, wrist/arm sensors, ring sensors, and finger sensors. Chest sensors measure the electrical activity of the heart, similar to an ECG, and most wearable devices use an optical technique called photoplethysmography (PPG). 

PPG uses green light and a light detector to measure the changes in the size of blood vessels and turn these measurements into heart rate readings. Devices that use this tech include Whoop, Fitbit, Polar, Oura, and Apple Watch (The Apple Watch also has ECG that is similar to a single-lead ECG).

Oura does it slightly differently than most wearables as it uses an infrared PPG. The accuracy of Oura’s HRV reading compared to an EKG is very high. The reason for Oura’s superiority stems from the fact that it measures HRV on the arterial side of the capillaries based on where it sits on the finger, whereas all the other devices mentioned measure HRV on the venous side of the capillaries. (This is typically on the wrist, so they’re measuring veins that don’t have as strong a signal as that on the arterial side.)

Based on the different types of measurement, you may see different HRV readings from different wearables. Also, the measurements are taken at rest and often at night. After obtaining the data, most wearables use the root mean square of the RR interval differences — or RMSSD —  to determine HRV. 

HRV is measured in milliseconds (ms), and it varies from person to person. For example, athletes tend to have a higher HRV. So, what might be normal for you might be abnormal for someone else. It’s better to monitor your HRV trends over time to notice changes in your health and fitness status.

It’s also important to understand that HRV declines with age. For example, one study in the Journal of the American College of Cardiology proposed that the average HRV is 72 ms for people in their 20s and drops to 64 ms for those in their 30s.

Factors That Affect Your HRV

Heart rate variability: elderly couple sleeping in their bed

Heart rate variability is a sensitive metric that is affected by various factors. For example, your HRV will likely be lower when you go to bed and ruminate over worries and anxieties from the day. 

Other factors that can decrease HRV are:

  • Alcohol 
  • Stress
  • Smoking
  • Lack of physical activity
  • A lousy diet
  • Caffeine consumption in the evening
  • Hypertension (high blood pressure)
  • High triglycerides
  • Metabolic syndrome

Factors that can raise HRV include:

  • Endurance exercise
  • Yoga 
  • Meditation
  • Breathing techniques
  • Good sleep hygiene

How to Improve Your HRV

If you’re looking to improve your HRV, focus on addressing the factors from above that lower your HRV and lean into the behaviors that increase your HRV.

Given the individual variations and the role of genetics in HRV, it’s important not to compare your HRV too much to that of others. Instead, it’s better to find your own personal baselines for heart rate, HRV, respiratory rate, and body temperature. Then, track how they trend and their fluctuations over time.

Heart Rate Variability: An Important Marker of Good Health

Doctor performing a stress test on a patient

Heart rate variability is a measure of the variation in time between heartbeats. In general, the higher your HRV, the better condition you’re in. However, rather than compare your HRV to others, it’s better to look at how it trends over time and in relation to your other biomarkers. If you’re looking to improve your HRV, there are factors you can focus on, like reducing stress and adjusting your diet.

If you notice your HRV levels dropping below normal, it might be time to take measures to improve it or check in with your doctor about treating any underlying conditions.

If you’re looking to understand, optimize, and improve your health status, sign up with Vital today. Vital makes it easy to collect all your data from wearables and apps in one place. With Vital, now you can challenge your friends or join a healthy community and grow together through shared motivation and support.

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