What is heart rate variability?

A recent survey found that one in five people own a smart watch or fitness tracker, which typically collects data like your heart rate, daily step count, walking pace and more. But recently, researchers have been shining the spotlight on other points of data, specifically heart rate variability, as a possible marker of adaptation and resilience.

Woman stretching before run

Heart rate variability (HRV) measures the variation of time in between each heartbeat. While your heart rate is the number of times your heart beats per minute, HRV measures how the time in between each heartbeat fluctuates. If your resting heart rate is 60 beats per minute, it’s unlikely that your heart is beating once every second. Instead, the time in between each heartbeat will vary – and your HRV is a measure of this.

This variation is controlled by the autonomic nervous system, which regulates your heart rate, breathing, blood pressure and digestion, among many other key tasks. The autonomic nervous system can be divided into two arms – the sympathetic nervous system (fight-or-flight) and parasympathetic nervous system (rest-and-digest).

The autonomic nervous system influences the heart on a cellular level

  • When the parasympathetic nervous system is activated, your heart rate slows down – allowing more time for changes in between heartbeats.
  • When the sympathetic nervous system is activated, your heart rate speeds up – reducing the capacity for any fluctuation between heart beats.

In short: a low heart rate variability means that your sympathetic (aka 'fight-or-flight') response is taking the driver’s seat, and a high heart rate variability indicates that your parasympathetic (aka ‘rest-and-digest') response is working as it should.

What your heart rate variability can tell you

Fight-or-flight mode

Measuring your HRV can determine an imbalance within the autonomic nervous system, which can be an indicator of increased stress. If you are spending too much time in the sympathetic division of the autonomic nervous system (aka in fight-or-flight mode), your heart rate variability will be low. If you spend equal or more time in the parasympathetic division (aka rest-and-digest mode), your heart rate variability will be high.

Vagal tone

The vagus nerve runs from the base of the brain to the large intestine. It touches major organs along the way (like the heart) and works to regulate heart rate, breathing, muscle function, circulation and more. While there’s a lot we don’t know about the vagus nerve, what we do know is that it’s a powerful regulator of the parasympathetic nervous system. By increasing calming neurotransmitters like acetylcholine and hormones like oxytocin – stimulating the vagus nerve promotes relaxation, digestion, sleep and healing.

Vagal tone is a measure of how the vagus nerve is functioning, which ultimately determines the activity of your parasympathetic nervous system – and vagal tone is indirectly measured through heart rate variability.

How well your body adapts to stress

In the same way that your heart rate variability can let you know how often you operate in fight or flight mode, it can also determine how well your body copes with stress. People with low heart rate variability are more easily affected by (or more frequently experience) stress, and those with high heart rate variability will find that they are less affected by stress or are better equipped to cope with it.


Tracking your HRV can tell you a lot about how you react to the environment and emotions around you. Your nervous system is sending you signs all the time that let you know how you’re coping with your environment, and tracking your heart rate variability is a helpful tool to tap into your physiological response.

The role of heart rate variability in health and longevity

In the last few decades, studies have reported that HRV decreases with age – which suggests that there is a decline in autonomic nervous system activity in older adults. Centenarians are a population of humans who experience delays in the onset of age-related health complications, outliving the average lifespan.

One study found that after measuring the HRV of centenarians, the results suggested an age-related increase in parasympathetic activity and a reduction in sympathetic activity. What this tells us is that a reduction in HRV can be a sign of declining health, and so monitoring HRV can support the early detection of age-related health complications – encouraging early interventions which may ultimately extend lifespan.

HRV reflects the heart’s capacity to respond and adapt to stress of all kinds (from everyday stress to the stress that strenuous exercise brings). A healthy heart is the key to longevity, and HRV offers a glimpse into how the heart is functioning. Optimal HRV reflects a healthy and balanced autonomic nervous system, which minimizes the impact of stress on the body and supports longevity as a result.

How you can improve HRV

There are plenty of ways to improve HRV (and support longevity as a result). Typical healthy habits like exercise, hydration and proper nutrition will all have a positive influence on your HRV. Additional mindfulness-based practices including meditation and diaphragmatic breathing have also been shown to benefit HRV.

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