What is heart rate variability (HRV) and why does it matter?

Heart rate variability (HRV) is a physiological measure that tracks the time between heartbeats. This non-invasive measurement is easily accessible and provides valuable insight into the activity of the autonomic nervous system. 

Research has shown that HRV is a reliable predictor of overall health and well-being. In this blog post, we will delve into the details of HRV, including its measurement and applications in areas such as sports performance, stress management, and medical research.

What is HRV?

Simply put, HRV is the variance of the time between heartbeats.

Multiple bodily functions control your heart’s behavior. While your heart’s rhythm is controlled by your sinoatrial node, or SA node, your heart rate variability, like many other automatic processes, is controlled by your autonomic nervous system, or ANS.

The autonomic nervous system consists of two branches:

• The sympathetic nervous system (often called “fight or flight”) reflects responses to things like stress and exercise. These responses often involve increases to your heart rate and blood pressure.
• The parasympathetic nervous system (often referred to as “rest and digest”) handles inputs from internal organs, like digestion or your fingernails and hair growing. It causes a decrease in heart rate.

Your HRV is an indicator of your body’s ability to manage these conflicting signals. This makes measuring HRV an effective way to capture how our body is doing while trying to maintain a state of balance in response to different stressors (training, lifestyle, etc.).

High vs. low HRV

In general, a higher HRV indicates better physical health. Oftentimes the body is better able to react to stress, and once the stress has been relieved, it can quickly bounce back. Your HRV is an indicator of how well your ANS and your heart work together.

A low HRV can indicate that your body is dealing with too much stress and your sympathetic nervous system is working overtime.

Keep in mind that HRV values can vary significantly depending on the individual, their age, fitness level, and overall health. It's important to note that there's no universally agreed-upon standard for what constitutes "low" or "high" HRV values, as they can vary based on the method of measurement and the population being studied.

That said, here is a rough overview of HRV values to use as a general guide but not to be supplemented for medical diagnosis:

Low HRV

Generally, lower HRV values might fall below 20-25 milliseconds (ms) for a standard deviation measurement of normal R-R intervals (NN intervals) between heartbeats. Low HRV might be associated with chronic stress, certain medical conditions, and a reduced ability to adapt to changes in the environment. 

Average HRV

A typical range for average HRV values can be around 30-60 ms, but this can vary. It's important to consider individual baseline and trends over time. Factors like age and fitness level can influence what's considered normal for each person.

High HRV

Higher HRV values are often indicative of a well-functioning autonomic nervous system and good adaptability to stressors. Well-trained athletes and individuals with strong parasympathetic activity might have HRV values above 60 ms or even higher.

Please keep in mind that these values are general guidelines and might not apply to everyone. HRV values can be influenced by various factors, including the method of measurement (time-domain, frequency-domain, non-linear methods), the duration of measurement, and the specific population being studied.

If you're interested in tracking your HRV or interpreting your own values, it's recommended to consult with healthcare professionals, exercise physiologists, or specialists familiar with HRV interpretation and the context of your health and fitness level. They can provide more personalized insights based on your specific situation.

Potential signs of higher HRV

Maintaining a high HRV is often regarded as a sign of good health and a properly functioning autonomic nervous system. However, excessively high HRV values could be an indication of certain conditions or circumstances that require further investigation.

It is crucial to bear in mind that symptoms linked to high HRV may also be related to other causes, so try not to look at them in a vacuum. Here are a few possible symptoms or situations to keep in mind:

• Extreme calmness: Individuals with exceptionally high HRV might experience a sense of extreme calmness or relaxation. While this can be positive, if it's accompanied by feelings of lightheadedness or dizziness, it could be a sign that your autonomic nervous system is excessively skewed toward parasympathetic activity.
• Fainting or near-fainting: Excessive parasympathetic activity can lead to a drop in heart rate and blood pressure, potentially causing fainting or near-fainting episodes.
• Vagal response: High HRV can sometimes indicate strong vagal tone, which is associated with rapid and intense shifts in heart rate, especially during activities like standing up quickly. This can lead to lightheadedness or dizziness.
• Digestive disturbances: An overly active parasympathetic nervous system might lead to digestive symptoms such as excessive bloating, flatulence, and changes in bowel movements.
• Excessive fatigue or low energy: While high HRV is generally associated with good health, in some cases, it could be linked to chronic fatigue or low energy. This might be due to an underlying medical condition that is affecting autonomic nervous system balance.
• Stress response issues: Parasympathetic dominance might make it difficult for your body to shift into a stress response when needed. This can impact your ability to handle acute stressors effectively.
• Underlying health conditions: While high HRV is often a sign of good health, it's possible that certain underlying health conditions might also lead to high HRV. It's important to consider other symptoms and consult a healthcare professional for a comprehensive assessment.
• Athletic training: Athletes or individuals engaged in intense physical training might have high HRV due to their cardiovascular fitness. However, it's essential to monitor for signs of overtraining and ensure that the high HRV is reflective of overall well-being.

Remember that having a high HRV is generally considered beneficial, but if you experience any unusual or concerning symptoms in conjunction with high HRV, it's advisable to consult with a healthcare provider. They can help determine whether these symptoms are related to your HRV, other health conditions, or other factors entirely.

Potential signs of lower HRV

Low HRV is often associated with reduced autonomic nervous system adaptability and can indicate various health issues. Here are some potential symptoms or conditions that might be linked to low HRV:

• Stress and anxiety: Low HRV is commonly seen in individuals experiencing chronic stress, anxiety, or emotional overload. It reflects an imbalance between the sympathetic and parasympathetic branches of the autonomic nervous system.
• Fatigue: People with low HRV might feel more mentally and physically fatigued. This can be due to the body's reduced ability to regulate energy and recover effectively.
• Insomnia: Sleep disturbances, including difficulty falling asleep or staying asleep, can be associated with low HRV. Poor sleep quality can further contribute to a decrease in HRV.
• Mood disorders: Conditions like depression, bipolar disorder, and post-traumatic stress disorder (PTSD) have been linked to low HRV. These disorders often involve disruptions in autonomic nervous system regulation.
• Cardiovascular issues: Low HRV can be a marker of increased cardiovascular risk. It's associated with hypertension, coronary artery disease, and other heart-related conditions.
• Inflammatory conditions: Chronic inflammation, whether due to autoimmune disorders or other reasons, can affect the autonomic nervous system and lead to reduced HRV.
• Diabetes: Individuals with diabetes, especially those with poor blood sugar control, might experience lower HRV.
• Chronic pain: Conditions causing chronic pain, such as fibromyalgia, can lead to lower HRV due to increased sympathetic nervous system activity.
• Gastrointestinal issues: Digestive problems like irritable bowel syndrome (IBS) can be associated with low HRV due to their impact on the autonomic nervous system.
• Medications: Certain medications, such as beta-blockers used for hypertension, can lower HRV.

It's important to note that experiencing one or more of these symptoms doesn't necessarily mean you have low HRV. Low HRV is best assessed by properly measuring and interpreting heart rate variability data.

Some of the many factors that affect HRV

These causes of stress can be chronic (such as obesity, alcohol abuse, or a long-term illness), and studies have shown a correlation between low HRV and the incidence of coronary disease.

Temporary causes of stress can also affect HRV in the short term. Work stress, over-exercising, or poor-quality sleep can affect your HRV.

Common potential causes of low HRV

Low HRV can be caused by a variety of factors, including:

1. Chronic stress: Prolonged stress and anxiety can lead to an imbalance in the autonomic nervous system, reducing HRV. The sympathetic branch might dominate, leading to decreased variability between heartbeats.
2. Age: HRV tends to decrease with age, as the autonomic nervous system's regulation becomes less flexible.
3. Health conditions: Certain medical conditions like diabetes, cardiovascular diseases, hypertension, and other chronic illnesses can lead to reduced HRV.
4. Physical inactivity: A sedentary lifestyle can contribute to lower HRV. Regular physical activity is associated with higher HRV.
5. Smoking: Smoking and exposure to tobacco smoke have been linked to decreased HRV.
6. Poor sleep: Sleep plays a crucial role in regulating the autonomic nervous system. Chronic sleep disturbances or poor sleep quality can lower HRV.
7. Inflammation: Conditions associated with chronic inflammation, such as autoimmune diseases, can affect HRV.
8. Medications: Certain medications, like beta-blockers used to treat hypertension, can lower HRV as they influence the autonomic nervous system.
9. Genetics: There can be a genetic predisposition to lower HRV in some individuals.
10. Overtraining: Intense or excessive exercise without sufficient recovery time can lead to reduced HRV. This is often seen in athletes.
11. Mental health disorders: Conditions like depression and post-traumatic stress disorder (PTSD) can impact HRV.
12. Nutritional factors: Poor diet and nutrient deficiencies can affect autonomic nervous system function and consequently HRV.

It's important to note that some individuals naturally have lower HRV due to their physiological makeup, and it might not necessarily indicate a health problem in such cases. However, persistently low HRV, especially when accompanied by other symptoms, should be discussed with a healthcare professional. Keep in mind that HRV is a complex parameter influenced by multiple factors, and its interpretation should be done in a clinical context.

The connection between sleep and HRV

Sleep plays a crucial role in regulating the autonomic nervous system (ANS). This then, in turn affects HRV. The autonomic nervous system consists of the sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) branches. Their balance is reflected in HRV.

Here are some ways sleep and HRV are connected:

Sleep quality

Adequate and high-quality sleep is associated with higher HRV. During deep sleep stages (such as slow-wave sleep and rapid eye movement (REM) sleep), the parasympathetic branch of the autonomic nervous system becomes more active, leading to increased HRV. Conversely, disrupted or poor-quality sleep can lead to decreased HRV.

Circadian rhythms

The body's internal clock, known as the circadian rhythm, influences sleep patterns and HRV. Disturbances in the circadian rhythm, like irregular sleep-wake schedules or jet lag, can impact HRV.

Sleep disorders

Sleep disorders such as sleep apnea, insomnia, and restless leg syndrome can lead to altered ANS activity and subsequently affect HRV.

NREM and REM sleep

Different sleep stages have varying effects on HRV. REM sleep is associated with increased sympathetic activity and lower HRV, while NREM (non-rapid eye movement) sleep, especially the deeper stages, is linked to increased parasympathetic activity and higher HRV.

Sleep deprivation

Lack of sufficient sleep, whether it's acute or chronic, can lead to an imbalance in the autonomic nervous system, with a bias toward sympathetic dominance and reduced HRV.

Sleep recovery

Getting adequate sleep after periods of sleep deprivation or strenuous activities can help restore autonomic balance and increase HRV.

Given the intricate relationship between sleep and HRV, it's essential to prioritize healthy sleep habits for overall well-being. Regular sleep patterns, sufficient sleep duration, and good sleep quality contribute to maintaining a balanced autonomic nervous system and higher HRV. 

If you're concerned about your HRV or sleep patterns, it's advisable to consult with a healthcare professional or sleep specialist for personalized guidance and recommendations.

What is the Right HRV?

Everybody’s HRV is different. It can vary due to so many factors, like age, gender, and overall health. It also fluctuates throughout the day, and between days. And, for most people, it gradually goes down as they age.

While researchers have compiled statistical data on typical HRV ranges by age and gender, the more important metric is how your individual HRV changes over time.

The study of HRV is ongoing. If you have questions or concerns about your health, speak to your doctor.

Taking care of yourself

In conclusion, HRV is a powerful tool in understanding the physiological state of an individual and can provide valuable insights into overall health and well-being. By understanding HRV, individuals can take steps to optimize their health and well-being.

But remember that each individual is different. So before changing up your routine or jumping to conclusions, it’s advisable to speak to a specialist about any heart-related concerns you may have.