The small variations in the amount of time between heartbeats make up a measure called heart rate variability (HRV). These small fluctuations of around a fraction of a second are due to the influence of the autonomic nervous system, a part of the nervous system that influences automatic processes in the body like heart rate, blood pressure, and breathing.

Heart rate variability can reflect how adaptable the body is. In general, when the heart rate is highly variable, it reflects that the body can adapt to many kinds of changes. People with high heart rate variability are generally less stressed, while low heart rate variability is generally a sign of the body being less resilient and struggling to handle changing situations.

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What is Heart Rate Variability (HRV)?

Heart rate variability (HRV) is a measure of the variation in time between each heartbeat. It is used as a marker of resilience and physiological flexibility.

A healthy heart is not like a metronome but instead has complex oscillations that are constantly changing. This allows the cardiovascular system to adjust quickly to sudden physical and psychological challenges to the body's balance.

Heart Rate Variability reflects how adaptable the body is. In general, when the heart rate is highly variable, it reflects that the body can adapt to many kinds of changes and is less stressed. On the other hand, a low heart rate variability can be a sign that the body is less resilient and struggling to handle changing situations.

Low heart rate variability is associated with current or future health problems because it reflects decreased resilience. Low HRV is also more common in people with higher resting heart rates since when the heart beats faster, there is less time between beats and, therefore, less opportunity for variability. Elevated heart rates and lower HRV may occur with conditions like diabetes, high blood pressure, irregular heartbeats (arrhythmia), asthma, anxiety, and depression.

How Does Heart Rate Variability Work?

The variation between each heartbeat that is reflected in HRV is controlled by a part of the nervous system called the autonomic nervous system (ANS). Your heart has to be able to react to changes in the environment, the body, and life. This is controlled in large part by signaling from the ANS and brain.

The heart has its own integrated pacemaker known as the sinoatrial (SA) node that controls the heart rate. The SA node maintains a heart rate of around 100 beats per minute. Inputs from the brain and ANS modulate this rate.

Heart rate changes depending on various factors, including physical activity, breathing rate, psychological and other stress, environmental conditions, and inputs like caffeine, medications, and foods. In general, the heart rate is slower when you are resting or relaxed and faster when you are active, stressed, or in danger.

The hypothalamus in the brain located above the brainstem constantly processes information and transmits signals to the rest of the body through the ANS that influence HRV. The ANS receives input from parts of the central nervous system that process and integrate stimuli from the body and external environment and contribute signals and outputs that help the body maintain balance. The ANS influences the entire body, including blood vessels, internal organs (stomach, intestines, liver, kidneys, bladder, genitals, lungs, heart), pupils and sweat, salivary, and digestive glands. This system works largely autonomously, without your conscious effort to control the "automatic" functions of the body that you do not consciously think about, such as heart rate, blood pressure, digestion, dilation and constriction of the pupils of the eyes, kidney function, and temperature control.

The two main branches of the ANS influence the rate of your heartbeat and the degree of variability:

• The parasympathetic system helps coordinate the relaxation response and slow heart rate, which makes more room for changes between beats or a higher HRV
• The sympathetic division of the ANS influences the stress or "fight or flight" response that raises the heart rate, reducing space for variations in beats resulting in a lower HRV

Both branches are engaged all the time to varying degrees, depending on the circumstances. The push and pull of these two parts of the ANS produce the variation in time between heartbeats, aka HRV. Therefore HRV is a good measure of how well your autonomic nervous system is functioning.

How Is Heart Rate Variability Measured?

These variations in heart rate are very small and require specialized equipment or devices to detect. HRV is usually measured in milliseconds (ms).

An electrocardiogram machine (ECG or EKG) can detect heart rate variability by measuring the heart's electrical activity using sensors attached to the skin of your chest. This can be done for a brief period or with a monitor that can be worn for several days or hours to measure more data.

Outside of a medical setting, there are several commercial devices that can be worn to monitor heart rate and variability. These can take several forms, such as wrist straps or watches, devices that attach to the fingertip like a pulse oximeter, and straps that wrap around the chest to detect heart rate.

What's A Good Heart Rate Variability Number?

HRV is influenced by many factors and can vary between individuals. A good HRV number varies with age, other health conditions, fitness level, environment, genetics, and other individual factors. When assessing HRV, it is useful to look at trends in your individual numbers over time since HRV is very personal and dynamic.

Several metrics are used to quantify the variability in the time period between successive heartbeats that defines HRV. HRV is commonly measured using RMSSD, the root mean square of successive differences between heartbeats. This reflects the beat-to-beat variance in heart rate and estimates the ANS-mediated changes reflected in HRV.

A normal HRV for adults generally ranges from below 20 to over 200 milliseconds.

A higher HRV, or a wider variation of time intervals between heartbeats, reflects a balanced autonomic nervous system, showing that the body can adapt well to internal and external physical and psychological stressors.

On the other hand, a lower HRV, or less variation of time intervals between heartbeats, reflects a lack of adaptivity between fight-or-flight and relaxation, indicating an imbalance in the ANS. This indicates that the body is working harder to adapt or recover from stressors like illness, asthma, high blood pressure, cardiovascular disease, overtraining, diabetes, anxiety, or depression. A lower HRV is a strong, independent predictor of future health problems.

Heart Rate Variability by Age and Gender Breakdown

HRV tends to decrease with age, with the normal HRV range declining for both men and women as they get older. Although gender tends to impact HRV less than age, especially in older age groups, younger women (under 30) tend to exhibit a higher parasympathetic tone and a lower sympathetic modulation than men resulting in lower average HRV.

While there is a normal range of variability, a common range of RMSSD measures of HRV for 20-29-year-olds falls in the 24-62 millisecond range, while the mid-range of HRV for 60-69-year-olds is closer to 16-28. Overall, in some data sets, the average HRV for men is right around 40, while for women, it is around 37.

But since HRV fluctuates greatly throughout the day, from one day to the next and from one person to another based on many individual factors, it is most useful to track your own individual HRV over time versus trying to fit into a set range.

How to Improve Heart Rate Variability

HRV can be one helpful metric to track to give some insight into overall adaptability and physical health. Fortunately, several lifestyle habits have been shown to help improve HRV and resiliency.

Balanced Regular Exercise

Research shows that regular exercise improves HRV. However, it is essential to refrain from overtraining or regularly exercising too hard without recovery periods, as this can decrease HRV.

Hydration

Proper hydration with water and electrolytes influences the volume of your blood, which helps maintain proper circulation and delivery of oxygen and nutrients to your body. Even mild dehydration can induce physiological stress that lowers HRV. On the other hand, alcohol has been shown to raise heart rate and lower HRV.

Manage Stress with Mindfulness

HRV is significantly impacted by stress, both psychological and physiological. Therefore meaningful stress management practices like meditation, yoga, tai chi, breathwork, or spending time in nature are important for optimizing your HRV. Another way to improve HRV and manage stress is by focusing on gratitude. Research shows that HRV increases during gratitude journaling exercises.

Sleep Deeply

Chronic stress with sympathetic nervous system activation is associated with insomnia and other sleep issues. The parasympathetic nervous system must be activated and balanced for a healthy deep sleep. Getting enough consistent deep sleep can help improve HRV. Non-REM sleep is associated with a higher HRV, while sleep disruption and awakenings during the night increase sympathetic activity, elevate heart rate and blood pressure, and lower HRV. Implement a healthy sleep environment and routine to improve your HRV.

Eat a Balanced Diet with Plenty of Greens

Food allergies, sensitivities, and inflammatory ingredients like processed sugars and fats stress the body. Research has shown that eating lots of leafy greens such as spinach, kale, mustard greens, and lettuce results in a more balanced HRV.

Find a Work-Life Balance

Having meaningful work and life purpose can positively impact stress levels. On the other hand, factors that reduce the work-life balance, like long commutes and working overtime, lower HRV scores.

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Summary

Heart rate variability, or HRV, is a measurement of the variation in time between heartbeats. HRV results from the constant interplay of the two parts of the autonomic nervous system, the sympathetic branch that functions to increase heart rate, blood pressure, and breathing rate, and the parasympathetic, which works to reverse that stimulation and restore the body to a state of relaxation and calm. Therefore HRV reflects how well your autonomic nervous system is functioning with ​​resilience, flexibility, and balance, which is critical to mental and physical health.

HRV is one helpful metric to track to give some insight into overall adaptability and physical health. HRV can be measured with an electrocardiogram (EKG) or specialized wearable devices like a watch or chest strap. HRV is influenced by many factors and can vary between individuals.

A good HRV number varies with age, other health conditions, fitness level, environment, genetics, and other individual factors. Generally, a normal HRV for adults ranges from below 20 to over 200 milliseconds. A high HRV is more desirable than a low HRV because it demonstrates that your body can recover more easily from stress.

A higher HRV, or a wider variation of time intervals between heartbeats, reflects an autonomic nervous system that is balanced and resilient to stress. A lower HRV, or less variation of time intervals between heartbeats, reflects a lack of adaptivity or imbalance in the ANS that results from illness, overtraining, or other chronic stressors.

Fortunately, several lifestyle habits help to improve HRV and resiliency. Fueling the body with balanced nutrition and leafy greens, regular physical activity, staying hydrated, and managing stress with mindfulness and self-care all result in a more balanced nervous system and HRV.