What is Heart Rate Variability (HRV)?
The popularity of wearable technology has introduced many people to heart rate variability (HRV), a metric that provides insight into the health of your nervous system and physical condition.
Dr. Talha Farid, MD, UnityPoint Health, explains what exactly this complex measure means, why a high HRV is a sign of good health and when you should talk to your doctor.
What is Heart Rate Variability (HRV)?
Heart rate variability is the beat-to-beat change in your heart rate.
“Your heart rate isn’t fixed. It constantly responds to different parts of the day, activity levels and other external factors. HRV measures the tiny, millisecond variations in time between one heartbeat and the next,” Dr. Farid says.
HRV shows how healthy your autonomic nervous system (ANS) is, which handles automatic functions like your “fight or flight” stress response — the body’s reaction that prepares you to either fight danger or flee from it.
Understanding the Numbers: What is a Good HRV?
When you check your HRV number on a wearable device, a high number is a positive sign.
“It’s essentially a measure of your body’s capability of coping with stress and other demands. A high HRV means your ANS can quickly switch between the calming ‘rest and digest’ state and the activating ‘fight or flight’ state,” Dr. Farid says.
What’s a Good HRV Number or Range?
It’s extremely difficult to give a single, absolute number for what constitutes a “good HRV.” HRV is highly variable based on several personal factors:
- Age: As you get older, your HRV naturally decreases.
- Baseline: The most meaningful comparison is often against your own past readings. If your fitness improves, your number should rise.
- Gender: Females traditionally have a slightly higher HRV than males.
- Physical fitness level: Elite athletes may have a high HRV (around 200 milliseconds).
HRV During Sleep
Interestingly, your HRV during sleep is often higher than it is during the day.
While your actual heart rate is lower because you’re resting, the variability (the beat-to-beat change) is actually higher.
“Measuring HRV during sleep is beneficial, because it removes all the other stresses from your autonomic nervous system. This makes the sleep HRV a truer measure of your underlying autonomic and cardiovascular health,” Dr. Farid says.
Meaning of Low HRV
A consistently low HRV suggests your nervous system is stuck in a state of high stress or activation.
Why is my HRV so Low?
A low HRV can be an indicator of:
- Aging
- Chronic stress or anxiety
- Illness or infection
- Poor cardiovascular health
- Poor sleep hygiene
Symptoms of Low HRV
Low HRV doesn't cause direct symptoms. Instead, it’s a reflection of symptoms you’re already experiencing. For example, if you’re sick, your HRV will drop in response to the stress your body's feeling.
What is a Dangerously Low HRV?
Dr. Farid says there’s no specific number for a dangerously low HRV outside of your personal context.
"If you feel great, you probably won't just suddenly see one low number and have a serious problem," he says.
When your HRV suddenly drops below your normal range, look for other symptoms: Are you getting sick? Are you experiencing extreme emotional stress? HRV is just one part of a much larger system.
How to Improve or Increase Heart Rate Variability
The good news is that you have control over many of the factors that lead to better HRV. Anything that supports your cardiovascular health also positively affects your HRV.
The best strategies to improve or increase HRV include:
- Improve sleep hygiene: Prioritizing quality, consistent sleep allows the nervous system to fully recover.
- Increase physical fitness: Regular exercise is one of the most effective ways to boost your HRV.
- Losing weight: Improving body composition reduces the physiological stress on your system.
- Reduce stress: Practices like meditation and yoga can significantly help reduce stress and improve HRV.
When to Talk to Your Doctor About HRV
Dr. Farid advises caution when interpreting data from wearables.
“Don’t panic. If you’re consistently concerned about your readings or have symptoms that accompany a low HRV, talk to your primary care doctor or a cardiologist to get a medical assessment. Don’t base your entire health on a single HRV number,” he says.