What Does Heart Rate Variability Mean?

Having a variable heart rate is not only normal, but it's also needed.

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Updated on June 23, 2022

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The human heart can beat more than 115,000 times a day.¹ Most of the time, you don't pay any mind to the rate at which your heart beats, but how it varies can tell you a lot.

Heart rate variability (HRV) is one of many measurable indicators of heart health. Similar to how blood pressure and cholesterol levels can be associated with medical conditions, so too can HRV.² But HRV doesn't just help with evaluating heart health. Athletes may also be able to use their HRV to optimize training.³

What Is Heart Rate Variability?

While heart rate is the number of times the heart beats per minute, HRV is a measure of the change in timing between successive heartbeats.

Having variation in heart rate is not only completely normal, but it is also necessary. Your heart is constantly keeping blood flow at a consistent level, keeping pace with your body's needs.⁴

For example, your heart may beat at a steady rate of 60 beats per minute while you are resting. Suddenly, when your alarm clock rings and you get up to face the day ahead of you, your heart rate picks up to keep pace with your activities.

During exercise, your heart rate needs to increase to provide blood flow for your working muscles and distribute blood to carry oxygen throughout your body. If your heart rate did not increase with exercise, you would quickly become lightheaded and perhaps even faint.

How Does Heart Rate Variability Work?

The heart's electrical system controls heart rate.⁵ The electrical system sets heart rate based on what's happening with the following⁴:

Nervous system
Cardiovascular system
Respiratory system
Hormones
Circadian rhythm
Body temperature
Metabolism

Each of these factors has an effect on the beat-to-beat variation of the heart that is responsible for HRV.

To understand how HRV works, you also have to consider the roles of the parasympathetic and sympathetic nervous systems. The parasympathetic system is what's in control when you are at rest. The sympathetic nervous system is responsible for the fight-or-flight response. The two systems are counterparts and both are tied closely to the heart rate and HRV.

Each breath you take has an impact on HRV through stimulation of the parasympathetic nervous system.⁴ Then, when fight or flight kicks in, the sympathetic nervous system releases the hormones of epinephrine or adrenaline, causing an increase in heart rate. So the parasympathetic and sympathetic nervous systems have different effects on heart rate, leading to HRV.

What Does Heart Rate Variability Tell Us?

HRV can reveal information about cardiovascular health and fitness.

Generally, a higher HRV is a good sign of heart health and cardiovascular fitness.⁴

Athletes tend to have greater degrees of cardiovascular fitness since exercise training improves the heart's efficiency. Because of this, they also tend to have higher HRVs.⁶ Athletes may use HRV as part of specific training protocols to enhance endurance and performance, though more research is needed to determine how best to incorporate HRV into training protocols.^3,7

A higher HRV doesn't always mean better heart health, though. For example, arrhythmias, which are potentially serious irregular heartbeats, can cause high HRV.⁴

Generally, reduced HRV is associated with an increased risk of death, arrhythmias, and heart attack.⁸ Abnormally low HRV has also been associated with early death, heart failure, arrhythmias, and sudden cardiac death.²

Aging, as well as conditions like inflammatory disease, chronic pain, mood disorders, and sleep disorders such as sleep apnea and insomnia can decrease HRV.^4,9

How Do You Measure Heart Rate Variability?

To measure HRV, you need to have your heart monitored.¹⁰ This monitoring can last anywhere from less than five minutes to 24 hours.⁴ Medical devices such as an electrocardiogram, heart rhythm monitors, pacemakers, and internal cardiac defibrillators can all measure HRV.

Some people, like competitive athletes looking to improve their performance, want to measure their HRV at home. To do this, HRV can be measured with wearable fitness devices such as smartwatches.¹¹

How Can You Improve Your Heart Rate Variability?

Humans don't have control over many factors that influence HRV. However, studies have shown that HRV can be improved in a few ways.

Increasing exercise can improve HRV.¹² Exercise trains your heart to pump more efficiently, and its effect on HRV may be due to its effect of stimulating the parasympathetic nervous system.¹³

Other factors that have been linked to an improved HRV include^14,15,16:

The Mediterranean diet
Stress reduction
Meditation
Breathing exercises

Treatment of conditions that have been shown to be associated with low HRV may improve HRV, for example, treating sleep apnea.¹⁷

When to See a Healthcare Provider

If you're concerned about your heart health and notice heart rates that are abnormally low or high in relation to your activities, it's time to see a healthcare provider. This could include things like a heart rate that does not increase with exercise or a heart that is racing while at rest. Certain arrhythmias—like atrial fibrillation, an irregular, often rapid heart—can affect HRV. These conditions should be evaluated and treated by a provider.

Summary

HRV is just one of many indicators of cardiovascular health and fitness. It's normal and healthy to have variability in heart rate throughout the day based on various activities. Athletes tend to have higher HRV, which corresponds with higher cardiovascular fitness, and HRV data may be incorporated in some training protocols to improve endurance. In general, HRV can be improved with a structured exercise program and possibly with other healthy lifestyle techniques such as stress reduction and a healthy diet.

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