What Is Heart Rate Variability?

Medically Reviewed by Jabeen Begum, MD on February 12, 2024
7 min read

Your heart rate is the number of heartbeats you have in a minute. Your heart rate depends on what you're doing at the time. So, if you're resting or relaxed, your heart beats slower, and if you're moving or stressed, your heart beats faster. Your body adapts to your energy needs and your emotional state and changes your heart rate over time.

These differences in your heart rate change the amount of time between each heartbeat. This is your heart rate variability.

Your heart rate variability can give you a clue about your physical and mental health.

Your autonomic nervous system controls your heart rate variability. Your autonomic nervous system is the part of your nervous system that controls functions that you need to survive, such as your heart rate, blood pressure, digestion, and breathing. It does this without you having to think about it, whether you're awake or asleep.

Your autonomic nervous system has two main parts:

  1. Sympathetic nervous system. This part controls your "fight-or-flight" response. If you're scared, startled, or anxious, your sympathetic nervous system signals your adrenal glands to release adrenaline. This raises your heart rate and blood pressure so you're ready for any physical activity.
  2. Parasympathetic nervous system. This part is the opposite of your sympathetic nervous system, and it controls your "rest-and-digest" processes. It slows your heart rate and blood pressure, especially after you've been in a fight-or-flight response.

The hypothalamus, a small region in the middle of your brain, constantly processes information from your senses and transmits signals to the rest of your body through your autonomic nervous system. The signals can either relax (parasympathetic nervous system) or stimulate (sympathetic nervous system) different functions in your body, including your heart rate variability.

  • It can show imbalances in your autonomic nervous system, which gives you a clue about your stress levels. Your heart rate variability is determined by the balance between the responses in your sympathetic and parasympathetic nervous systems. A high average heart rate variability suggests your autonomic nervous system is working in a "rest-and-digest" mode more often than a "fight-or-flight" mode. This is good news for your heart and emotional health.
  • It gives you feedback on your lifestyle habits. Tracking your heart rate variability over time can show you how incorporating healthy habits, like regular exercise, good sleep hygiene, meditation, and mindfulness, affects your health.
  • It can help you plan your workouts. Once you have an idea of your average heart rate variability, you can plan high-intensity workouts for days when your heart rate variability is higher than average and low-intensity or rest days for when your variability is lower. Whether you're a serious athlete or not, this can help prevent you from overtraining and hurting yourself.

Differences in the amount of time between each of your heartbeats is measured in fractions of a second. So, you need specialized devices to detect your heart rate variability.

Several methods are available, including:

EKG. This is the most accurate way of getting your heart rate variability. You can have an EKG in your doctor's office, or they can give you a device called a Holter monitor to take home. A Holter monitor can record your heart's activity over 24-48 hours. You will get a better idea of your heart rate variability with a Holter monitor because it gives more readings over a longer period and during more types of activities.

Chest strap heart rate monitors. Competitive runners and serious athletes often use these to monitor their heart rate while they train. These monitors have a device that wraps around your chest and transmits readings to your phone or computer. These monitors will give you the most accurate readings outside of a medical EKG or Holter monitor.

Wrist-worn fitness devices and trackers. Various companies over the years have launched apps and heart rate watch systems (such as Fitbit and the Apple Watch) that can help you check your heart rate variability. They take readings through the skin on your wrist. They're the least accurate, and their accuracy is highly dependent on how your wrist device fits. However, they are still a good way for most people to get an idea of how their lifestyle is affecting their heart health.

Factors that affect your heart rate variability include:

External and lifestyle factors. Several outside and lifestyle factors that can change your heart rate variability. For instance, the following tend to lower your heart rate variability:

  • More social stress, anxiety, and depression
  • Being in a hot environment (cold environments don't seem to affect it very much)
  • Exposure to noise
  • Having more body weight or more fat mass
  • Drinking more than one to two drinks of alcohol per day, depending on your size and weight
  • Drinking coffee (but it may not be by very much)
  • Smoking
  • Pain
  • Exposure to mercury
  • Night-shift work

Physiological factors. Physiological factors that affect your heart rate variability include age, sex assigned at birth, and circadian rhythm.For instance:

  • Your heart rate variability tends to go up until you reach age 15, after which it goes down. It continues to go down throughout the rest of your life.
  • People assigned female at birth tend to have a slightly lower heart rate variability than those assigned male at birth.
  • Heart rate variability tends to be higher when you sleep than after you wake up.

Certain medical disorders. Heart rate variability tends to be lower in people with some medical conditions, including:

  • Heart disease, such as cardiac insufficiency, high blood pressure, and after a heart attack
  • Metabolic disease, such as diabetes
  • Lung disease, such as chronic obstructive pulmonary disease
  • Kidney disease, such chronic kidney insufficiency

High heart rate variability

When your heart rate has a high variability, it suggests that your body is adapting well to many kinds of situations. People who have a high heart rate variability may have better heart health and may be more adaptable to stressful situations.

Heart rate variability and stress

People with a high heart rate variability tend to be less stressed and happier than those with a low heart rate variability.

Low heart rate variability

Low heart rate variability may be a sign of current or future health problems because it shows that your body isn't adapting to changes well. You may have a low heart rate variability if you have a high resting heart rate. People with a low heart rate variability often have medical conditions, such as diabetes, high blood pressure, heart arrythmia, asthma, anxiety, and depression.

What is a dangerously low heart rate variability?

It can be difficult to interpret heart rate variability. Every person has a variability that's "normal" for them, and this generally lowers as you age. Low variability isn't likely to cause a medical emergency, although it may be a sign that you need a checkup or are at a risk of medical problems in the future.

Normal heart rate variability

In healthy adults, average heart rate variability is 42 milliseconds. The range is between19 and 75 milliseconds. Athletes and other people who are very fit may have a much higher heart rate variability.

How to improve heart rate variability

A few ways to raise your variability include:

  • Improve your physical condition. The main ways to do this are to eat a healthy diet and exercise regularly.
  • Take care of your mental health. Reduce and manage your stress level, and make sure you follow your doctor's advice to manage any of your mental health conditions, such as anxiety or depression.
  • Try biofeedback training. This is an alternative therapy that can help you manage your stress and anxiety through breath control.

What is a good heart rate variability?

Every person is different and has a variability that's "normal" for them. Studies show that in healthy adults, heart rate variability is between 19 and 75 milliseconds.

Is it better to have high or low heart rate variability?

In general, it's better to have a high heart rate variability because it means that your body is adapting to change and stress more efficiently. Athletes and fit people tend to have a high heart rate variability.

Is Apple Watch heart rate variability accurate?

Very few studies have been done to determine the accuracy of heart rate monitoring on the Apple Watch. One small study from 2018 showed that the Apple Watch was accurate when assessing heart rate variability during a relaxed and emotionally stressed state. However, it only takes short readings when you are sitting still, so it tends to miss measurements. The researchers, therefore, couldn't say how it performs over a period of time and during exercise. This means that a heart rate variability estimate from your Apple Watch will probably be lower than it would be with an EKG, Holter monitor, or chest strap monitor.

Heart rate variability is the slight difference in the amount of time between your heartbeats. Your heart rate variability is controlled by the balance between a couple of different parts of your autonomic nervous system: the "fight-or-flight" response and your "rest-and-digest" response. In general, it's better to have a high heart rate variability because it suggests your autonomic nervous system is working in a "rest-and-digest" mode more often than a "fight-or-flight" mode. Outside your doctor's office, you can measure your heart rate variability using chest strap monitors or wrist-worn fitness trackers, which are fairly accurate. You may want to pay attention to your heart rate variability to plan your workouts and monitor your stress levels.