Heart Rate Variability: What it is, and why you should be measuring it

Chances are, you've measured your heart rate at some point in your life. But have you ever measured your heart rate variability?

Heart rate variability (HRV) is quickly becoming one of the most concrete, evidence-based approaches to measuring your health, recovery, and fitness. For decades, the common technique of measuring heart rate has been by counting the number of beats per minute. HRV, on the other hand, measures the time BETWEEN each heart beat. While it may seem that the time between your heart beats is the same for each pump, it's actually always altering by several milliseconds. How much it changes beyond normal values can provide useful information on how much physiological stress our body is under.

Generally speaking, HRV measures how different the time between each heart beat is. Having heart beats that all have similar times between them would be considered LOW heart rate variability, and is mostly considered "bad". When the time between heart beats alters, this is HIGH heart rate variability, and is associated with good health, and proper recovery. By monitoring your HRV, it can tell you a lot about the state of your body.

For example, if you monitor your resting HRV every morning (as you should) and you suddenly notice the variation in the time between your heart beats has decreased (less time between beats) than your usual values, than it is a good indicator your body is in a stressed state. In these cases, you may be emotionally stressed, overtrained, injured, or physically ill. In fact, research has shown that HRV can predict the onset of illness several days in advance - before you even feel the symptoms! And that's only one of the reasons why you should be measuring the time between your heart beats!

Figure 1. The time between each beat of the heart (R-R Interval) is measured by using an ECG reading and can determine if our body is in a stress or recovery state

To understand WHY there are  changes in the time between our heart beats, and how it affects us, we need to understand the autonomic nervous.

The autonomic nervous system is comprised of two parts - sympathetic and parasympathetic. The sympathetic nervous systems is commonly referred to as the "fight or flight" response. It is activated in times of stress (including exercise), and causes our heart rate and blood flow to increase, while also increasing the power output of our muscles. However, if the sympathetic nervous system is activated, it also results in increased stress hormones (such as cortisol) circulating in our body - which decreases performance. The parasympathetic nervous system has been termed our "rest and digest" response. In a mostly parasympathetic state, your muscles relax, your heart rate slows down, and you are generally in "recovery mode". While one system may be more activated at any given time, it is important to note that you are never 100% sympathetic or parasympathetic, but a combination of both. If one becomes more active over the other, it can drastically affect our performance or ability to properly recover. That's where measuring your HRV comes in.

Fight or Flight response
Rest or Digest response
Body is under stress
Body is in recovery state
Increased performance
Increased recovery
Less time between heart beats
More time between heart beats

Heart Rate Variability can be used to determine if we are in a stressed state (sympathetic) or a recovery state (parasympathetic)

The difference in time between your heart beats (HRV), is an indirect measure of whether you are in more of a sympathetic (stressed) or parasympathetic (recovery) state. For example, if your HRV decreases (i.e. LESS variation between heart beats) above normal resting levels, than it is an indicator that your body is under physiological stress. In these cases, you likely have more stress hormones circulating in your body due to an increased sympathetic nervous system (fight or flight) response. This could be as a result of a high intensity workout, emotional stress, physical injury, or increased immune system activity due to the on-come of illness.

In the case of high intensity exercise, we want our sympathetic nervous system to activate. By doing so, we get performance increases such as increased blood flow, greater stroke volume (blood being pumped), and more power output, among others. However, as previously mentioned, in these cases, we also get stress hormones released which decrease performance if not properly managed. This is one of the many reasons why recovery from exercise is so important. If we still have the byproducts of a high intensity workout (and increased stress response), than we physiologically aren't fully recovered and thus won't be able to perform at 100%. A decreased resting HRV reading can be an indicator of our sympathetic response still being active, and our body not being fully recovered. In this case, the best approach might be to scale down the intensity of exercise until HRV readings have returned to normal. For athletes and especially coaches, this is helpful in establishing a training schedule that allows for optimal performance and to avoid overtraining. If an individual or athletes HRV is decreased more than 10% above normal resting levels, it is likely more beneficial to lower the intensity of the workout, or in extreme cases halt training and focus on recovery practices.

Likewise, when we are injured or feeling ill, the automatic response is for the body to activate the sympathetic nervous system to help fight off whatever the ailment is. In these cases, our HRV readings will be decreased and there will be less time between our heart beats. In fact, research has shown that HRV can be used to predict the on-come of illness several days before the individual even feels the symptoms!

research has shown that HRV can be used to foresee the on-come of illness several days before an individual even feels the symptoms! 

Although many health professionals and sports coaches are now using HRV to monitor health and recovery, recent technological advantages have made it easier for any individual to do the same - at home on their own. Many heart rate monitors (like the  new Polar H7 & H10 models) have HRV reading functions. The data you get from these monitors are much more in depth than what I have gone in to in this article, so having a health or fitness professional read the raw data is recommended. However, there are cell phone apps now available that read your HRV using these types of heart rate monitors and using their own algorithms, give you a simple HRV score. If you want to measure your own HRV, my advice is to use one of these apps to determine what your baseline HRV 'score' is, and if you notice a change to adjust your training or recover. Two of my favourite apps are Elite HRV or iathlete which both measure HRV.

Whether you are an elite athlete, health and fitness enthusiast, or just want to live a healthy and (relatively) stress-free lifestyle - measuring your HRV can be a useful tool and I recommend you do it. Join the revolution and measure the time between your beats!

Got questions? Send em my way.
My email is KalanAnglos@Gmail.com
I can be found on all social media platforms - @KalanAnglos

Kalan is an Exercise Physiology & Sports Performance Expert who brings an evidence-based approach with practical-based knowledge to the world of combat sports and human performance. He is recognized as a Certified Strength & Conditioning Specialist (CSCS) with the National Strength & Conditioning Association (NSCA), and has obtained his MSc. Kinesiology degree at the University of Victoria. Through his masters thesis research, Kalan has established and implemented the KFit Test Battery for Combat Sport Athletes which is used by both Karate BC & Karate Canada as their standard fitness test for  athletes across the country. Additionally, Kalan is an exercise physiology lab instructor at the University of Victoria, and trains individuals (including athletes) every day to help meet their fitness needs and goals. He has many years of experience both as an elite athlete and high performance coach and is knowledgeable in the many fields surrounding fitness and training for sports performance.