Understanding Heart Rate Variability: What is HRV?
While heart rate measures the number of heartbeats per minute, heart rate variability, or HRV, measures the fluctuation in time between each heartbeat (in milliseconds). The amount of time between heartbeats isn’t always the same. In reality, the time between heartbeats fluctuates. These subtle fluctuations might seem minor, but they are normal and can be incredibly insightful. Tracking and understanding the trends of our personal heart rate variability provides us with a unique snapshot of our body’s resilience, adaptability, and functionality and shows us how our nervous system state affects our overall heart health. Monitoring our HRV can even inform us of the onset of illness before we feel under the weather, and also of our fitness recovery status. Ever feel unsure if your body is ready for an intense training session, or if a rest day would better serve you? Monitoring your HRV can help with this!
What Factors Influence HRV?
Heart rate variability is influenced by many factors within and outside our control. Age, gender, hormones, and emotions affect HRV, as well as sleep hygiene, nutrition, hydration status, physical fitness, and alcohol and caffeine intake, amongst other factors. A higher HRV signifies more variation in the amount of time between heartbeats, while a lower HRV signifies less variation in the amount of time between heartbeats meaning the intervals of time stay more consistent.
As a general rule of thumb:
- A higher HRV (more variation in time between heartbeats) is associated with rest-and-digest, general fitness, and good recovery.
- A lower HRV (less variation in time between heartbeats) is associated with fight-or-flight, stress, or illness.
The Autonomic Nervous System has two branches, or opposing operating system settings — the parasympathetic (rest-and-digest) system and the sympathetic (fight-or-flight) system. How one’s heart beats is significantly influenced by which branch is dominant at any given time. When the parasympathetic, or ‘rest-and-digest’ system is dominant, it tells the heart to slow down, making room for more variability between heartbeats and leading to a higher HRV. On the other hand, when the sympathetic, or ‘fight-or-flight system,’ is dominant, it instructs the heart to speed up, limiting the space for variability between heartbeats and resulting in a lower HRV. By balancing the two branches of our nervous system, our Autonomic Nervous system helps us respond to daily stressors and regulate some of our body’s important systems like heart rate, respiration, and digestion.
What Are the Benefits of Measuring HRV?
Measuring your HRV provides helpful insights into your athletic performance, your immune system health, and your stress management. Monitoring HRV can be a tool to help protect you from overtraining and help optimize your performance. A lower than baseline HRV can signify that your body could use more recovery time. For immune health, a downward trend in HRV can signal a challenged immune system. Monitoring your HRV for the goal of stress management can make you more aware of stressful situations and help you seek out more coping tools. HRV is a key indicator of your Autonomic Nervous System balance, which directly impacts your heart’s activity. With the growing popularity of fitness wearables, tracking HRV has become accessible and user-friendly. We’ll share a few popular fitness wearables for HRV at the end of this blog.
When is the best time to measure HRV?
Ideally, the best time to measure HRV is at night or during sleep. Nighttime HRV, a time when you are not engaged in exercise or cognitive activity, will give a more accurate reading of your overall status in a more holistic, comprehensive sense. Therefore, an HRV measurement from sleep reflects the truest state of your system. The best way to determine your unique normal is by using a wearable device that measures HRV in a controlled setting, like sleep, and establishing a baseline over a few weeks or months.
Is There A ‘Normal’ HRV?
It’s important to know there is no fixed ‘normal’ HRV. HRV fluctuates throughout the day due to various influences and activities. Generally, HRV values can range anywhere from below 20 to over 200 milliseconds. While some wearable devices track HRV continuously throughout the day, for valuable insights like illness onset or recovery needs, it’s more beneficial to focus on trends rather than on isolated readings.
Everyone’s HRV is unique!
Just like fingerprints, each person’s HRV is unique, and “high” and “low” HRV is relative to the individual. HRV is a highly sensitive and personal metric, affected by lifestyle, habits, age, genetic predispositions, and other factors. For some, HRV scores may naturally remain steadier, while for others, scores may fluctuate greatly. When it comes to optimizing your performance, a general goal is to aim to increase your heart rate variability over time. It’s essential not to compare your HRV to others as it’s not a competitive score. Just because one person has a higher average nighttime HRV than another, it doesn’t mean they are healthier than the person with a lower average.
It is true, however, that there is a general trend seen with age. As we age, our hearts tend to become more “rigid” and “robotic”, leading to a decrease in HRV. But remember, this is a general trend and individual experiences can vary greatly! The key is to focus on your own HRV averages and trends, use them to gain insights about your health and make necessary adjustments to support your longevity health journey.
When Working With HRV Think Longterm Trends
Recognizing short and long-term HRV trends can be extremely helpful. For example, let’s say you’re deciding whether to prioritize recovery or push yourself in a challenging training session one day. You could compare your HRV average from the previous night to your baseline nightly HRV average (usually read out first thing in the morning). If your HRV average from last night was significantly lower than your baseline nightly HRV average, this could mean that a recovery day would serve you more than a challenging workout. In contrast, if your HRV average from last night was higher than your baseline, that could indicate that you’re ready to go, and to push yourself with a challenging workout. Monitoring your HRV trends over a few weeks can confirm whether or not you’re successfully rebounding from taxing days like training, illness, or stress. When undergoing a major lifestyle change like starting a new job or moving to a new location, you can monitor HRV changes over those weeks or months to reveal how it’s affecting your health. Remember again that “high” and “low” HRV is relative to each individual.
Boost Health By Noticing HRV Patterns
Despite the common oversimplification, it’s not always true that high HRV is good, and low HRV is bad. There are instances where low HRV is appropriate and expected, for example after a strenuous workout that challenges your aerobic system or your muscle, it is reassuring to see the drop the next day, indicating that you really did work hard. If you decide you need a recovery day, and you engage in a mindfulness practice, sauna, or massage, it is helpful and affirming to see the next day’s HRV go back up. What matters the most is your HRV trends. Sometimes the HRV value is unexpectedly high or low, helping us to manage our day accordingly. In our practice, we have had several patients wake up with an unexpectedly low HRV. They postponed their high-intensity workout only to discover later in the day they have a sore throat and test positive for COVID. By resting and getting more sleep the next night, they may have assisted their immune system in its challenge. We have also had patients note after spending time with family and foregoing their usual careful diet and exercise, that their HRV rose considerably, showing the power and importance of emotional connection.
Understanding HRV isn’t about obsessing over the numbers. It’s about noticing patterns, observing how they relate to your lifestyle and behaviors, and using these insights to boost your overall health and well-being. Monitoring your HRV can help you reach peak productivity, manage stress, and fine-tune your training regimen.
What Are Recommended Wearables For HRV Monitoring?
In the age of wearable technology, tracking HRV has become more accessible than ever. For serious athletes, consider the WHOOP. Note this wearable requires a monthly membership to access a range of metrics. For those more focused on general longevity and/or biohacking, the OURA ring is a great option. Alternatively, the Garmin Forerunner 255 watch is a well-rounded option for general health, fitness, and recovery aid. Lastly, for those already using Apple products, later versions of the Apple Watch also have HRV tracking capability which is viewable from the health app on your phone.
In conclusion, heart rate variability is a fascinating and insightful metric to monitor. It provides a deeper understanding of how our bodies respond to stress, how well we’re recovering, and even when our immune system is challenged. While it may seem complex, understanding your unique HRV and how it fluctuates can empower you to make more informed decisions about your health and well-being. Just remember, it’s not about comparing your HRV with others but rather, understanding your unique patterns and what they can tell you about your own health.
What Is Heart Rate Variability (HRV)? by the Oura Team
Heart Rate Variability: An Old Metric with New Meaning in the Era of Using mHealth Technologies for Health and Exercise Training Guidance. Part One: Physiology and Methods. – National Library of Medicine, 2018 by Singh N, Moneghetti KJ, Christle JW, Hadley D, Plews D, Froelicher V. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6141929/
Photo by Ketut Subiyanto