What is Heart Rate Variability?

With the rise of wearable smart devices, which track health metrics like heart rate, blood oxygen levels and sleep, which had previously only been available in a medical or research setting have become accessible to us all. With that increased accessibility, has come a rise in interest in what the data actually says about your overall health and wellness. Heart rate variability (HRV) is one of these metrics.

What is HRV? Simply put, it is a measure of the variation in time between each heartbeat measured in milliseconds (ms). For those who are more visual, it’s represented as the highest point on the graph of a heart rate readout (often seen in your favorite medical drama). Far from being as steady as a metronome, the ms between each heart beat significant changes and that’s a good thing. Sometimes the beats are fast and close together like with exercise and sometimes they are slow and more spread apart.

There seems to be evidence that increasing HRV is a little bit like increasing physical strength: If you have consistently trained your body to be able to lift and carry heavy objects, when a friend suddenly needs help to move, it will not be as taxing on your body. In other words, your body is more resilient as it is trained for exertion. The same is true for HRV: if you have higher HRV throughout your day, then when an unexpected stressor (illness, emotional or physical trauma) pushes your heart rate far outside of your normal range you are less likely to experience a significant impact on your health or wellbeing. Essentially if you do a mix of things throughout your day that sometimes increases your heart rate and sometimes slows your heart rate down then you are training your heart to handle the variety life throws at it.

Since the late 1970’s medical professionals have noted that higher HRV was a predictor of survival after cardiac events. Along with predicting health outcomes, high HRV is associated with good cardiovascular health, fitness, improved mood, increased willpower, and resilience to stress and pain. Conversely, low HRV has been linked to systemic inflammation, persistent pain, depression, and low emotional flexibility and stress tolerance. In sport, high level athletes sometimes use HRV tracking to prevent overtraining, as too much training without adequate recovery can cause HRV to decrease.

So what can you do to train HRV? Not a surprise, but improving your strength and fitness can increase HRV. That said, physical fitness is not the only determinant of HRV. Breathing exercises such as resonance frequency breathing (RFB) are extremely effective in moderating HRV. RFB is a technique in which an individual intentionally takes slow deep breaths to help create a biofeedback loop that can increase HRV. The rate of breath varies from person to person, but generally it is around 4-7 breaths per minute. This breath training technique also helps explain why taking a few deep breaths when frustrated or before a big presentation helps you to feel prepared to manage whatever comes next. However, as steadying as a few breaths can feel in the moment, in order to create a long term improvement in HRV it is recommended to practice RFB daily for between 5-20 minutes.

Since starting to track my own HRV, I have noticed certain patterns: When I'm getting sick, my HRV will trend down in the days leading up to and during the time I feel ill, and then gradually return to normal as I recover. I can also see a flattening of my HRV after a longer duration of intense exercise when my body needs recovery time. This has helped me to structure my own planned physical activity to match what my body needs most, eg. restorative yoga instead of a strength training session when I’m already showing signs of being run down. It’s also been a helpful reminder to slow down and take some deep breaths more regularly. As a numbers and data driven person, understanding HRV has been helpful in supporting my own health and it could potentially do the same for you too.