What Is Heart Rate Variability?

Heart rate variability (HRV) is a metric that most wearable devices track, but what is Heart Rate Variability? This article goes over what HRV is, why it’s an important metric to know and track properly, the accuracy of HRV wearable tracking, and natural ways you can improve your HRV. 

 

What Is Heart Rate Variability (HRV)?

Heart rate variability (HRV) is the change or variability in the time intervals between consecutive heartbeats. If Heart rate is the number of heartbeats per minute, Heart rate variability is the fluctuation in the time intervals between those adjacent heartbeats.

 

The variability between heartbeats is complex and constantly changing. This variability is essential because it allows the cardiovascular and autonomic nervous systems to rapidly adjust to sudden physical or psychological challenges, maintaining balance and resilience in the body.

Why Heart Rate Variability (HRV) Is Getting So Much Attention?

HRV is controlled by two competing branches of the autonomic nervous system: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is your “fight or flight” response, which increases your heart rate, whereas the parasympathetic nervous system is your “rest and digest” mode, which decreases your heart rate. HRV essentially measures the changes between your heart beating faster and slowing down, depending on which branch of your nervous system is activated at any given moment. When you have high HRV, it means your body is responsive to both the sympathetic and parasympathetic systems, which tells how well your body moves between stimulus and rest.

 

Why Is Heart Rate Variability Important? 

A high HRV indicates better stress resilience, cardiovascular resilience, and better overall well-being. This is because your nervous system and heart have the health and resiliency to oscillate between stimulus and rest optimally. Low HRV does not directly mean your heart is structurally unhealthy, but it signals reduced resilience of your nervous and cardiovascular systems; spending more time in a state of stress than a state of relaxation. A low HRV can be a sign of overtraining, high stress, or even be a sign for the potential increase in risk of a cardiovascular event. In essence, HRV reflects your body’s ability to relax and engage in a stress response in a balanced way.

 

What HRV Tells Us About the Nervous System

HRV is in essence controlled by a primitive part of the nervous system that works behind the scenes to regulate breathing, heart rate, digestion, and many other automatic processes in the body. This metric indicates autonomic nervous system balance and adaptability, cardiovascular resilience, and your recovery capacity, but does not measure structural or electrical issues with your heart. 

 

When someone’s HRV is high, this means that the nervous system is equipped to oscillate between stress and rest in an efficient and quick way. A good example is to look at prey animals. Prey animals are able to move between stressful situations (running away from predators) and going back into a relaxed state with ease. They often do this because they are able to discharge the energy from a stressful situation through shaking or trembling.

 

Just like prey animals, someone with a high HRV is able to adapt to situations quickly and not stay stuck in a stressful state. This can look like being able to unwind, rest, and get enough sleep after a stressful day. On the other hand, staying stuck in sympathetic dominance (fight or flight) from overthinking or chronic anxiety, can lower HRV, and keep people stuck in stress response cycles for a longer period of time.

 

How Is HRV Measured?

HRV is most accurately tracked through an ECG or EKG in a medical setting. However, the average fitness minded person is most likely going to rely on a wearable to measure their HRV.

Some of the more accurate wearables to measure HRV include the Oura Ring & Whoop strap.

 

Wearables use Photoplethysmography (PPG) to detect blood flow changes in the vessels beneath the skin. Since there aren’t electrodes placed on the chest to measure the heart exactly, wearables aren’t 100% accurate. However, it’s still good data to see trends over time.

 

HRV is one of the most variable measurements there is, so you won’t be able to get much information from what your HRV looks like at one particular point in time. Give yourself a few weeks to track your HRV to get a general sense of your average HRV in relation to what’s going on in your life. This is the best way to assess your individual baseline.

 

What Affects HRV?

The main factors that contribute to HRV are stress, sleep quality and quantity, exercise and recovery, nutrition, hydration, and meditation and breathing practices. Alcohol can majorly impact HRV as well. Even one drink can dramatically drop HRV levels in a 24 hour period. 

 

Other influential factors include age (HRV tends to decline with age), hormonal changes (especially your menstrual cycle, menopause, or thyroid issues), illness or inflammation, caffeine intake, nicotine and drug intake, and your environment (even weather and altitude can affect HRV). Some data suggested by Whoop has shown that endurance athletes typically have higher HRV than strength athletes, women tend to have lower HRV on average than men, and HRV naturally goes down while you’re exercising hard (in the moment).

 

How to Interpret HRV

HRV is best interpreted over long periods of time with awareness of what is currently happening in your life. Because HRV fluctuates so much throughout a single day, the data doesn’t mean much unless it’s viewed as a trend. You can track your HRV every 24 hours, over months, or even across a year to see meaningful patterns. Tracking HRV for less than 24 hours may not provide an accurate picture.

 

It’s important not to compare your HRV to someone else’s. Your HRV is highly individualized. Consistently higher numbers typically mean you’re more able to handle acute stress. Focus on the collective measurements and trends over time. When your HRV is higher, your body has more capacity to allocate resources toward exercise and recovery.

 

How to Improve Your HRV Naturally

Simply put, HRV improves through living a healthy lifestyle. Getting a good night’s sleep is one of the easiest and most important ways to improve HRV. Managing stress is another way to improve HRV, which is easier said than done. Tools to manage stress include having a meditation practice, getting body work when you need it, and training properly (you want to veer away from overtraining). This could mean that in stressful times, you dial back your training. Fun social engagements are also an underrated and great way to destress.

 

Breathwork & HRV

Breathing techniques are some of the greatest tools you have to help regulate your nervous system. Your heart and your breath are deeply connected through the vagus nerve, which is in charge of the parasympathetic (rest and digest) nervous system. When you breathe slowly and deeply—especially on the exhale—you stimulate the parasympathetic nervous system, directly impacting your HRV by slowing down your heart rate with your breath. You can work with breathing techniques for any duration of time.

 

One of our trainers did a self study on breathwork and HRV during her yoga teacher’s training. She found that breathwork (she was also practicing yoga and had a meditation practice at the time) improved her HRV by 61% in the course of four months. She also found that her breathing and meditation practices also helped her get better sleep, which also positively impacted her HRV. Her findings speak to the impact that mindfulness and breathwork have on HRV. 

 

Using HRV to Guide Your Health Journey

You can use your HRV stats as a tool for assessing your overall nervous system and recovery health. You can also let your HRV stats guide your intensity and recovery days, but don’t make it the end all be all. Paying attention to HRV trends over time, can give a good sense of what is happening in your life and how it is impacting you. 

 

However, the problem with any fitness and health metrics is that people become reliant on them and disregard their own body’s signals and cues. It’s important to still learn how to listen to your body. 

 

Want to learn more about HRV? Listen to episode 238 of the Stronger Than Your Boyfriend Podcast: HRV- Heart Rate Variability

 

Sources Cited: 

Shaffer, F., & Ginsberg, J. P. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in public health, 5, 258. https://pmc.ncbi.nlm.nih.gov/articles/PMC5624990/

Tiwari, R., Kumar, R., Malik, S., Raj, T., & Kumar, P. (2021). Analysis of Heart Rate Variability and Implication of Different Factors on Heart Rate Variability. Current cardiology reviews, 17(5). https://pmc.ncbi.nlm.nih.gov/articles/PMC8950456/