HRV stands for Heart Rate Variability. Researchers and physiologists have been tracking and utilizing HRV for decades because it’s a useful indicator of several health-related issues (more about these later), but only lately has it grabbed the attention of athletes, coaches, biohackers and the general public.

The Oura ring tracks your HRV during the night which makes it an especially useful tool for tracking your HRV with little extra effort.

On the left, the Oura app draws your night-time HRV curve, as well as average and max HRV. On the right, your long-term HRV trend.



What You’ll Learn In This Article

We’ll cover the basics of heart rate variability in two blog articles. This article introduces you to HRV in general. You’ll learn:

  • What HRV is
  • What HRV tells you about your body
  • Why you shouldn’t compare your HRV to anyone else’s HRV
  • What you can learn from tracking your HRV

This second article in the series digs deeper into the science of HRV measurement and explains how and why Oura tracks HRV.

What Is Heart Rate Variability (HRV)?

A healthy heart beat contains healthy irregularities. Even if your heart rate is, say, 60 beats per minute, that doesn’t mean that your heart beats once every second – or at one-second intervals like a clock.

Rather, there is variation among the intervals between your heartbeats. The interval between your successive heartbeats can be, for example, 0.85 seconds between some two succeeding beats and 1.35 seconds between some other two.

Even though the difference is measured in parts of seconds, you can actually feel the difference.

Here’s a tip for anyone who wants to experience it: place a finger gently on your neck or wrist and find your pulse. You should feel that the longest intervals take place when you exhale, and the shortest intervals when you inhale.

R-R Intervals and Interbeat Intervals

How you calculate heart rate variability depends on what technology you use. Using an ECG, or electrocardiogram, it’s typically the R peak in the QRS complex that marks a heartbeat. Hence, the intervals between heartbeats are called R-R intervals.

With Oura, your heartbeats are analyzed with PPG (photoplethysmography). In the PPG signal it’s the steepest increase in the signal prior to the peak that marks a heartbeat. Instead of R-R intervals, we measure interbeat intervals, or IBIs. See the image below for what ECG and PPG signals look like.

Defining Heart Rate Variability

Heart Rate Variability is a measure which indicates the variation in your heartbeats within a specific timeframe. The unit of measurement is milliseconds (ms). For Oura, the measurement timeframe is 5 minutes.

  • If the intervals between your heartbeats are rather constant, your HRV is low.
  • If their length variates, your HRV is high.

There are different ways to calculate HRV, but they all have to do with the amount of variation in the intervals between heartbeats. Oura utilizes rMSSD (Root Mean Square of the Successive Differences), which is the most commonly used HRV formula. The figure below is an example of interbeat intervals in milliseconds.

Why Is Heart Rate Variability an Important Measure?

Why track HRV? The key is the phrase “healthy irregularities” we used in the beginning of the article. The type of variability indicated by HRV is perfectly normal. Actually, it’s desirable.

The Basics

To understand HRV, we first need to understand our nervous system and heart rate. Heart rate variability can be traced back to our autonomic nervous system.

The autonomic nervous system regulates very important systems in our body, including heart and respiration rate and digestion. The autonomic nervous system has a parasympathetic (rest) and a sympathetic (activation) branch. Heart rate variability is an indicator that both branches are functioning – the parasympathetic in particular.

Intrinsic heart rate is measured in the condition in which neither parasympathetic nor sympathetic regulation is present. When completely blocked from autonomic regulation, a healthy heart contracts at a rate of about 100 beats per minute (the number is individual, however).

Parasympathetic regulation lowers your heart rate from the intrinsic level, giving more room for variability between successive heartbeats. Parasympathetic regulation causes almost immediate changes that affect only a few beats at a time, after which the heart rate returns towards the intrinsic rate. Sympathetic regulation elevates your heart rate from the intrinsic level, and there is less room for variability between successive heartbeats. Sympathetic regulation affects several consecutive heart beats.

Put these together and we can formulate a rule that when the rest-related parasympathetic branch is active and the sympathetic branch is inactive, your heart rate is lower and HRV higher.

Put these together and we can formulate a rule that when the rest-related parasympathetic branch is active and the sympathetic branch is inactive, your heart rate is lower and HRV higher. Factors such as stress can lead to the withdrawal of parasympathetic activity, or activation of sympathetic branch even when you are resting, both leading to elevated heart rate and lowered HRV.

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Heart rate variability has been studied, for example, in the context of cardiovascular training.

When you start regular cardiovascular training, one of the fastest positive adaptations of your body is increased blood plasma volume, and subsequently increased stroke volume. As a result, your heart can keep the blood flowing and maintain adequate blood pressure at a lower heart rate. And as we remember, lower heart rate is regulated by the parasympathetic branch. Parasympathetic regulation causes longer interbeat intervals and elevated HRV.

In the long term, regular exercise also strengthens the heart muscle, which once again means lower HR and higher HRV.

On the whole, high heart rate variability is an indication of especially cardiovascular, but also overall health as well as general fitness. Generally speaking, it tells us how recovered and ready we are for the day. Also, HRV can react to changes in our body even earlier than heart rate. This makes it a particularly sensitive tool that gives us insights into our wellbeing.

Your Heart Rate Variability Is Unique

You shouldn’t compare your heart rate variability with other people, because HRV is affected by a number of internal and external factors such as age, hormones and the overall body functions, as well as lifestyle. Furthermore, at a given heart rate, women typically have a higher heart rate variability than men.

There are no generic guidelines for optimal HRV values – which is understandable considering there are several ways to both track and calculate it. The HRV value given by Oura (rMSSD5min) can range from anywhere below 20 to over 100 ms. HRV tends to be higher when you’re fit and healthy, but how high is high depends on the individual.

You shouldn’t compare your heart rate variability with that of other people.

Instead of comparing your HRV values with someone else’s (even people of same age and gender), you should concentrate on your own HRV and its trends. Also, for your daily HRV values to be comparable with each other, they should be tracked with the same method and in similar conditions.

Interested in tracking your heart rate variability? The award-winning Oura ring with the Oura app is one of the easiest, most comfortable ways to track HRV in the long-term.


Oura calculates your HRV for each night. Comfortable nighttime tracking means that the conditions for measurement remain the same. Consequently, you can easily compare your values, both in the short and the long term, and you don’t need to do anything else except wear the ring.

What Can You Learn From Your HRV?

Heart rate variability is one of the indicators of the state of your health and fitness, recovery and readiness. However, your HRV values, like your overall health and fitness, are a combination of several things, so pay attention to yourself and how you feel as a whole. HRV is a good indicator, but it’s still just one indicator. Don’t rely too much on it, or any other measure alone.

With that out of the way, here are some ways you can learn from your HRV values.

The first thing to pay attention to is your own HRV baseline. That is, your typical HRV when you’re feeling as you feel on average. Your baseline is the starting point for your HRV explorations. You will get an understanding of your HRV baseline after using the Oura ring for a while, because Oura shows you both the nightly HRV value and the long-term HRV trend.

After discovering your baseline, you’re ready to follow up how your lifestyle and health affect your HRV. If your HRV goes down, something might be burdening your body and/or mind. If your HRV goes up, something might be doing good for your body and/or mind.

Before increasing your training load significantly or making major changes to your nutrition, remember to consult your physician – especially if you don’t feel well or if you suffer from long-term illnesses.

The Oura app and Oura Cloud show you the previous nights’ HRV, indicating your current HRV status. You can also see your weekly and monthly HRV averages, which help you to create a bigger picture of your readiness in the long term.

Practical Examples

Below are some practical examples of how changes in HRV can be interpreted, both in the short and the long term. Bear in mind that you and your HRV are unique, so all the examples may not be applicable to your situation.

Average heart rate variability and lowest resting heart rate before (Mon 28 – Wed 30), during (Thu 31 – Tue 05) and after (Wed 06 – Sat 09) illness

  1. You might notice that a very intensive endurance exercise can acutely lower your HRV, but if you recover well, it will jump back up again soon. This is generally speaking a sign that your body handles the training load well. If your HRV doesn’t jump back up, you may have been training too hard or too often. Overall, it seems that regular endurance exercise does tend to increase HRV in the long run, and a high HRV value (compared to your baseline) means that your body should be ready for the next exercise.
  2. If you become stressed or don’t sleep well for a while, you could see your HRV values gradually dropping, indicating that your body might not be at its best, and you need to take some time for recovery.
  3. One interesting finding is that your HRV can jump down if you’re about to get sick – even before you develop any symptoms. If this is the case, and you can take it easy for a day or two, your body might fight off the disease. If you get sick, your HRV can stay quite low even after the symptoms are gone. This indicates that your body is still recovering, and isn’t ready for maximal performance.
  4. Smoking and alcohol consumption can reduce HRV. You will most probably notice that your HRV goes down momentarily after a night out in town.
  5. If you’re an endurance athlete or otherwise exercise-oriented, these research findings* might interest you: among recreational endurance athletes, it seems that the level of HRV predicts training response for several weeks of training. If you have high HRV, your body can be expected to respond positively to high intensity training. If you have low HRV, your body can be expected to respond positively to high volume of low intensity training.
  6. Overall, HRV drops with dehydration, but jumps back to its baseline level with good hydration. As discussed, both exercise and alcohol can cause dehydration – as can long bouts in the sauna (for all you Finns out there!).

If you’re interested in tracking your HRV but don’t have the tools for it, have a look at the new Oura ring in the Oura Shop. If you have an Oura ring, you can dig deep into your HRV data in the Oura Cloud.

What Is Heart Rate Variability (HRV) & Why Does It Matter?

Heart rate variability (HRV) seems to be on everyone’s lips these days, at least those who are interested in monitoring their own or their clients’ sleep, recovery, performance or overall health. The phenomenon itself is not new, but its use in everyday language and in widely available devices is a fairly new development. Many professional and consumer wearables list HRV as one of the markers that they measure, and sports, wellness and performance coaches and professionals should understand the basics of this fascinating phenomenon. Without diving too deep into the science of HRV, this blog will discuss HRV from a practical perspective: what it is, what it can tell you about your body’s physiology, and what you should be aware of when interpreting it. Future blogs in this series will broaden the topic to practical applications and the somewhat complex relationship of HRV to things like stress and recovery.

“Higher HRV has been found to be associated with reduced morbidity and mortality, and improved psychological well-being and quality of life.”

Heart rate variability or HRV is the physiological phenomenon of the variation in the time interval between consecutive heartbeats in milliseconds. A normal, healthy heart does not tick evenly like a metronome, but instead, when looking at the milliseconds between heartbeats, there is constant variation. In general, we are not acutely aware of this variation; it’s not the same as the heart rate (beats per minute) increasing and decreasing as we go about our daily business. You can get a sense of your HRV if you feel your pulse on your wrist while taking a few deep breaths in and out: the interval between beats gets longer (heart rate slows down) when you exhale and shorter (heart rate increases) when you inhale, a phenomenon called respiratory sinus arrhythmia. In addition to respiration, HRV is influenced acutely for example by exercise, hormonal reactions, metabolic processes, cognitive processes, stress and recovery.

How to Measure HRV?

Reliable HRV analysis requires accurate measurement of each heartbeat and the time between beats. There are different technologies for calculating HRV, but it’s beyond this blog to discuss them comprehensively. If you want to dig deeper into the principles of measuring HRV and different HRV variables, I recommend for example the Task Force article on heart rate variability. In short, ECG-based methods detect the R wave in the QRS complex and calculate the time between R waves (R-R interval; Fig. 1). This is what, for example, the Firstbeat Bodyguard does: it can detect the heartbeat at 1 ms accuracy (1000HZ) for very accurate HRV analysis in most people of different body types and age groups. Most of the widely available wearable devices use PPG or photoplethysmography to detect the heartbeat optically by measuring the wave of blood flow, for example from the wrist or ear, and then calculate the inter-beat interval or IBI. Comparison between different methods is always challenging, and this is certainly true with HRV – and beyond the scope of this blog. However, different methods and devices, if used correctly and systematically, can produce interesting and useful information for the user.

Fig. 1 An ECG graph showing a series of QRS complexes. The time between heartbeats (R-R interval) varies naturally from beat to beat, and deeper analysis of this variation (HRV) provides a lot of valuable information about the body’s physiological status.

Heart Rate Variability and the Autonomic Nervous System

HRV is regulated by the autonomic nervous system (ANS), and its sympathetic and parasympathetic branches, and it is commonly accepted as a non-invasive marker of autonomic nervous system activity. The sympathetic branch of the ANS is the stress or fight or flight system, getting us ready to act, react, and perform – to meet the different demands that life throws at us. The parasympathetic side is characterized as the rest and digest system that allows the body to power down and recover “once the fight is over”. The sympathetic branch activates stress hormone production and increases the heart’s contraction rate and force (cardiac output) and decreases HRV, which is needed during exercise and mentally or physically stressful situations. Conversely, the parasympathetic branch slows the heart rate and increases HRV to restore homeostasis after the stress passes. This natural interplay between the two systems allows the heart to quickly respond to different situations and needs.

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Why Does Heart Rate Variability Matter?

In a normal, healthy situation, HRV should increase during relaxing activities, for example meditation or sleep, when the parasympathetic nervous system should dominate (see Fig 2 for an example). On the other hand, HRV naturally decreases during stress, when elevated sympathetic activity helps the body keep up with the demand. Thus, HRV is typically higher when the heart is beating slowly, and lower when the heart starts to beat faster, for example during stress or exercise. The HRV level changes naturally from day to day, based on the level of activity and amount of, for example, work-related stress, but if a person is chronically stressed or overloaded – physically or mentally – the natural interplay between the two systems can be disrupted, and the body can get stuck in a sympathetically dominant fight state, with low HRV and high stress hormone levels, even when the person is resting. This is very consuming on the body and can result in various mental and physical health problems.

Fig. 2. A person’s HRV graph (RMSSD in ms) over 24 h shows how HRV drops to almost zero during exercise (parasympathetic activity is withdrawn) and increases significantly during meditation and sleep. This is reflected as green recovery state in the Firstbeat Lifestyle Assessment graph, and is considered a meaningful, healthy response.

Genetic factors explain about 30% of the overall HRV level, but a person can improve their individual HRV by improving their health, fitness, stress management and recovery skills. High HRV is generally considered an indicator of a healthy heart, and higher HRV has been found in many studies to be associated with reduced morbidity and mortality and improved psychological well-being and quality of life. We must live with what the genetic lottery has given to us, and even if some general reference values are available, comparison to other people’s HRV values is not meaningful. The good news is that lifestyle has a powerful effect on HRV. We can take active steps to improve our lifestyle, be physically active and strive for a better balance in our lives, and in the process, will likely see improvements in our HRV as well.

Practical Applications for Utilizing HRV?

Firstbeat has developed ways of utilizing HRV in real-life conditions. The HRV data is turned into valuable and understandable feedback that helps to perform better, make correct training and coaching decisions, and improve wellbeing and health. Firstbeat Lifestyle Assessment is a professional-grade stress and recovery monitoring tool for wellness coaching. Firstbeat Sports is a complete solution to optimize training load and recovery for sports teams. Firstbeat is also trusted by top brands in wearable markets to help you make the best possible health, fitness and performance decisions. You can find Firstbeat features in over a hundred products.

Searching for that eureka moment with a client?
Firstbeat’s new guide shows how measured stress & recovery data can inform wellness professionals’ decisions and let clients unlock the best version of themselves.

Heart Rate Variability vs. Heart Rate

Today’s market inundates us with countless self-quantifying metrics, wearables, and apps that promise to change the way we approach health and fitness. It can be time consuming to sift through the BS to figure out what works best.

Heart rate (HR) and heart rate variability (HRV) have received a great deal of attention recently. Both metrics have many pros and cons that should be considered before using either one, though. In order to determine when to use these metrics correctly, it is important to understand the basic science behind each one.

What’s the difference between HR and HRV?

Heart rate (HR) is measured in beats per minute. It does not require exact times – just the average of the beats in a given time period. For example, a 60 beats per minute HR could mean 1 beat per second or it could mean an average of 1 beat every 0.5s, 1.5s, 0.5s, 1.5s, etc.

Heart rate measurement is a simple test that has been in existence for thousands of years due to the low-tech requirements for measurement.

Generally, a low HR indicates rest, while a high HR corresponds with exercise or exertion.

While heart rate focuses on the average beats per minute, heart rate variability (HRV) measures the specific changes in time (or variability) between successive heart beats. The time between beats is measured in milliseconds (ms) and is called an “R-R interval” or “inter-beat interval (IBI).”

While heart rate focuses on the average beats per minute, heart rate variability (HRV) measures the specific changes in time (or variability) between successive heart beats.

Generally, a low HRV (or less variability in the heart beats) indicates that the body is under stress from exercise, psychological events, or other internal or external stressors. Higher HRV (or greater variability between heart beats) usually means that the body has a strong ability to tolerate stress or is strongly recovering from prior accumulated stress.

At rest, a high HRV is generally favorable and a low HRV is unfavorable. When in an active state, lower relative HRV is generally favorable while a high HRV can be unfavorable.

HRV is actually an umbrella term for many different calculations and analysis methods. When applying these calculations correctly, the Autonomic Nervous System (ANS) can be precisely measured. The ANS is tied to every automatic process in the body and comprises of two main branches that control the body’s stress and recovery processes. It regulates blood sugar, body temperature, blood pressure, sweat, digestion, and much more. Using HRV to gain an understanding of the state of your ANS at any given moment is a huge advantage when tackling specific goals, identifying obstacles, or measuring progress.

Using HRV to gain an understanding of the state of your ANS at any given moment is a huge advantage when tackling specific goals, identifying obstacles, or measuring progress.

Since the ANS ties to so many biological systems and processes, HRV also links cardiovascular activity to the respiratory system, digestive system, and other recovery and stress related systems.

Since HRV focuses on the imperceptible changes between each heartbeat (in milliseconds), it is much more complex and requires higher degrees of accuracy than heart rate. But thanks to recent technology improvements, consumer grade heart monitors and smartphone apps can do all of the measurement work and neatly present the insights needed for decision making.

The Pros and Cons of Heart Rate


  • Easy to measure
  • Can measure during exercise
  • Can target aerobic exercise or specific “zones”
  • No need for extreme accuracy to use it
  • Great gauge of cardiovascular exertion during exercise
  • Vast numbers of devices and wearables of varying quality/accuracy exist


  • Limited to mainly measuring cardiovascular activity
  • At rest, heart rate is a vague indicator of internal activity at best and inconsistent at worst
  • Vast numbers of devices and wearables of varying quality/accuracy exist

The Pros and Cons of Heart Rate Variability


  • The most precise non-invasive measurement of Autonomic Nervous System activity (responsible for recovery and the body’s response to stress among other things)
  • Integrates the nervous system, cardiovascular system, and respiratory systems
  • Able to detect physical, digestive, environmental, psychological and other stressors
  • Can be measured by affordable consumer-grade heart rate monitors
  • Only takes 2 minutes per day for 95% of the benefit
  • Can be used to “train” the brain and nervous system to operate at peak performance with live biofeedback


  • Difficult to measure during exercise or while moving (though unnecessary usually)
  • Accuracy requirements limit the use of some trendy wearable HR monitors
  • Sometimes presented as a “magic bullet”
  • Various measurements of HRV can be confusing if presented improperly

When To Use Heart Rate

Heart rate and heart rate variability are often considered similar metrics, but they have completely different uses when used correctly.

Heart rate is best used during exercise. It is a great tool for training the cardiovascular system or monitoring the effects of training on the cardiovascular system in real time.

Heart rate is best used during exercise.

When To Use Heart Rate Variability

HRV is best used during a rested state (usually first thing in the morning or during rested activities such as meditation). It is a great tool for understanding overall health, resilience, and ability to tolerate stress from all sources.

HRV is best used during a rested state.

HRV can be used as a daily check-in with the body to determine its readiness to tolerate stress on a given day. In this regard, HRV is commonly used to optimize and individualize training programs based on a person’s’ readiness or recovery state. Also, HRV can be used to determine how various lifestyle choices affect health and performance by trending HRV and the correlated events over time. Luckily, apps do the hard work for you!

Imagine if your Apple Watch could tell you which days were best for you to do a workout, and what kind of workout you should do. Well it can, sort of, thanks to a hidden feature that few people have yet discovered or know how to use.

Heart rate variability, or HRV, is a new metric that reveals your stress level and whether you have recovered from your last workout. It has been added to lots of high-end sports watches in recent years, including Apple Watch since watchOS 4 & iOS 11.

Here’s how you can use it to optimize your training, reduce your risk of injury, and know when to take a well-earned rest day.

‘Listen to your body’ or ‘no pain, no gain’?

How do you know when you should train, and how hard? If you’re feeling aches and pains, should you take a break or train through it?

A lot of people say you should listen to your body, and never work out if you don’t feel great. The problem with that advice is that if you took it literally, you might end up never working out at all.

Running, cycling, swimming and most other sports come with an element of pain. That’s all a part of the deal. “No gain without pain,” as the saying goes. If it was easy, then everyone would do it. If you want exceptional results, you must push yourself harder than most people are willing to do. But how hard?

It’s a perennial problem for every athlete, whether you are a serious baller or a weekend warrior. Push yourself too hard and you risk getting injured, which could set you back months. Don’t push yourself hard enough and you’ll never make any gains.

How heart rate variability can help

Heart rate variability is a way of detecting the level of stress your body is under. Generally speaking (and a little counterintuitively), the higher your HRV, the lower your stress levels.

Lots of different things put your body under stress. Some of the most common causes are sickness and worrying, which are obviously not good things. But stress is not always a bad thing. Exercise, for example, is good for you, but it also increases your stress levels, sometimes for many hours after you finish a workout.

So HRV can be a complicated stat to interpret. However, if you follow the trends in your HRV over time, you can start to recognize patterns in how it changes, and how your body is responding to exercise, anxiety and sickness. When your HRV is unusually low, that may be a sign that you are under the weather, in which case you should probably skip a workout. Or at least go for a low-intensity workout, or do something relaxing instead, like some meditation or yoga.

Check your heart rate variability readings with the Health app on your iPhone.
Photo: Graham Bower/Cult of Mac

How to find your HRV in the Apple Health app

To measure your HRV, you need a Series 1, 2 or 3 Apple Watch. (The original “Series 0” model does not support HRV).

To get an HRV reading, you can use either the Workout or Breathe apps on your watch. Once you have completed a workout or breathing session, your HRV reading is displayed in the Health app on your iPhone, although you will have to do a bit of digging to find it.

In the Health app, go to the Health Data tab and tap on Heart. Then scroll down to Today and you should find your HRV data listed. If it doesn’t show up there, this probably means your watch has not taken a reading today.

What exactly is heart rate variability?

As the name suggests, heart rate variability is a measurement of the amount that your heart rate varies over time. Apple measures this with a metric called SDNN, the standard deviation between two normal heartbeats (that’s the N and N bit).

In other words, a low HRV means your heart rate is more rhythmic like a metronome, while a high HRV means your heart is not so rhythmic — like when I try to dance. Actually, it’s not quite as bad as my dancing. HRV is measuring very subtle differences, which can only be detected by sensitive equipment like your Apple Watch (more on that later). So even when you’re HRV is high, it should still feel pretty regular.

The regularity of your heartbeat is controlled by your sympathetic and parasympathetic nervous systems. When you exercise, the sympathetic nervous system kicks in to make changes in your body. When you finish exercising, your parasympathetic nervous system returns your body to its normal state.

As a part of this process, the sympathetic nervous system elevates your heart rate and makes it more regular, whereas the parasympathetic nervous system lowers it again when you have finished and allows it to become less regular and more responsive to your body’s needs from one moment to the next.

The Breathe and Workout apps will probably give you different results

Since your HRV changes when you are exercising versus when you are at rest, you are likely to get different results when you use the Workout app versus when you use the Breathe app. So it’s a good idea to use both, to get a fully rounded picture of your HRV over the day.

To check these different readings, open the Health app. On the HRV screen, tap on Show All Data and then select a specific day. You can check all the individual readings taken when you used the Workout and Breathe apps for that day.

How to use and improve your HRV

There’s more to HRV than just idle curiosity. When you get used to looking at your HRV and you have established a baseline (i.e. what normal readings look like for you), you can then use it to help you decide what kind of workout you should do.

When you have a low HRV, that suggests your body is under some stress. Maybe you did an intense workout the previous day and your body is still recovering from it, in which case you have earned yourself a rest day.

When your HRV is higher than average, that might mean you’re in top form and your body is ready for a more challenging workout like a HIIT session.

If you’ve been unwell — from a cold, for example — you might notice that your HRV is lower than usual, and it might be wise to hold off on exercise until it returns down to your normal level.

Remember that HRV is just one metric, and it’s not infallible. You should use it as an extra indicator of how you are doing. Obviously, if you feel like death warmed over, it’s not a great idea to do a workout however high your HRV might be.

How does your heart rate variability compare to norms?

Like most stats relating to the human body, HRV can vary a lot from one individual to another. What is normal for one person may not be normal for someone else, and these differences are not usually anything to worry about. Highly trained individuals tend to have a higher HRV than untrained people. And HRV tends to decline with age. There are also differences between genders. And those with existing heart conditions may have a lower HRV.

That is why it is important to watch how your personal HRV changes over time and get a feel for what is normal for you — your baseline.

That said, if you are interested in how your HRV compares with other people’s, a paper published by The Journal of the American College of Cardiology found the average SDNN for someone in their 20s was 72ms, while in their 30s this went down to 64ms.

Don’t stress the importance of HRV

It can be tempting to look at these stats and worry about them if you don’t think they look right. The problem with that is that HRV is a measurement of stress, and worrying will really stress you out. In fact, worrying can have a far bigger impact on your HRV level than exercise.

So if you are otherwise healthy, and you find these stats worry you, then just don’t look at them. Seriously.

Improving HRV accuracy

Measuring and interpreting HRV is a tricky business, once the exclusive domain of qualified medical professionals. Apple Watch is great because it democratizes this information, giving us mere mortals access to it as well.

But Apple Watch is not (yet) a medical-grade device, and HRV is a very subtle and tricky thing to measure. Some experts even claim that it is impossible to measure with the kind of wrist-based sensors used by Apple Watch. You can boost the accuracy of your HRV stats by connecting a Bluetooth chest strap, like the Polar H10 Heart Rate Sensor.

The undiscovered secrets of Apple Watch

HRV is just one more example of how far Apple Watch has come since it launched three years ago. With each update to watchOS, Apple adds more useful fitness metrics. In fact, Cupertino’s wearable can now provide so many stats that a lot of them are easy to miss. (Another one is the heart rate recovery feature I wrote about previously.)

It is probably no accident that Apple hid these advanced features, because making sense of them requires some knowledge. But if you make the effort to understand exactly what your Apple Watch is telling you, stats like HRV can really help you take your training to the next level.

HRV metrics help us track one of the most important parts of our body: Our autonomic nervous system (ANS). This is responsible for helping your brain and its control centers send signals to your heart, muscles, and glands; it helps regulate your stress, digestion, heart functions, and more. Inside the ANS, there are two mini-systems at work: The sympathetic (which regulates your “fight or flight” stress impulses) and parasympathetic (which regulates your energy and helps your body recover during rest periods).

In an ideal world, the two work in harmony to give you the energy you need and conserve it when you don’t. A high heart rate variability (HRV) average, for instance, indicates that your parasympathetic system is doing its job helping your body recover and regulate.

But let’s be honest: We don’t always live in an ideal world. We can take on too much stress, recover poorly, drink, overtrain, and generally fail to take care of our body. When that happens, our sympathetic system is doing more work, leading to lower HRV readings and often higher BPM while at rest.

HRV lets us spy on the balance between your sympathetic and parasynthetic nervous system at any given moment, giving us a peek into how our body is recovering from illness, stress, or workouts. Like tracking your BPM, you need context, which means tracking it regularly and comparing readings with your activities.

Tip: Your variability average is only the tip of the HRV-tracking iceberg; if you use a third-party app on your iPhone and an external heart rate monitor (or camera-based monitor), you can access more detailed metrics to help you better understand how your sympathetic and parasympathetic systems are working together.

Unlike BPM and blood pressure, there’s no “healthy” or “unhealthy” general number for a high or low HRV average: It varies depending on the person, which means that if you’re interested in tracking your nervous system, you need to regularly take heart measurements to get a good picture of what “high” and “low” values look like for you; ideally, you’d want to take HRV measurements in the morning when you first wake up, so that you can establish a baseline.

What can you learn from HRV tracking?

At a basic level, you can see how well your body is recovering from exercise, illness, or general stress. If you’re having a crazy week at work and your HRV average is lower than normal each morning, it can indicate that your body needs more rest and relaxation to balance out your stress.

What that rest looks like varies between people: hanging out with friends can help raise your parasympathetic system and your HRV average, as can engaging in activities you enjoy, deep breathing, yoga, meditation, and regular resting periods.

As an athlete, I find HRV monitoring particularly useful because it can help me tailor my workout programs: If my HRV average is too low the night after a hard workout or skate, I know I pushed myself too hard and will take it easy until my average stabilizes back to my baseline. It allows me to work hard when I know my body’s ready for it, but take breaks when I need to so that I can prevent overtraining.

You can also use your HRV baseline to figure out when you prefer exercising, how certain food affects your body, when you start to get sick, and a lot more — it’s all about context.

So how do you calculate your HRV average and other metrics?

Thankfully, you don’t have to do all the complicated math yourself: There are multiple different wearables available that measure your heart and your HRV, including:

  • EKGs (expensive)
  • passive electric monitors like the Polar heart strap
  • the Apple Watch
  • Other photoplethysmography techniques (like camera-based heartbeat readings)

These different hardware options all have different software associated with them: Most HRV apps can produce your variation average (a time-based datapoint), but many programs also offer more thorough time- and frequency-based HRV metrics.

How Apple calculates HRV

Apple currently records HRV averages in your iPhone’s Health app through Apple Watch readings (as well as any third-party apps that have chosen to write data to the repository). When you first put your Apple Watch on for the day, you’ll trigger an HRV morning reading; the wearable monitors your heartbeat steadily for one minute, then uses under-the-hood calculations* to come up with your HRV average, displayed as ms (milliseconds) in the Health app for iPhone.

*Apple currently uses SDNN to track HRV in the Health app; it doesn’t gather any other HRV data from your Apple Watch, nor does it allow third-party HRV apps to write anything but SDNN data to the Health app.

While Apple’s average is useful to get a basic idea of your HRV patterns, the company doesn’t yet offer you a more detailed look at any other time- or frequency-based HRV data (though it does store your beat-to-beat readings and timestamps). There’s also no obvious way to force an HRV reading outside of the Apple Watch’s automated morning and evening readings; starting a Breathe session on your Apple Watch will record the right data, but it’s not noted anywhere for users curious about their HRV data and getting subsequent readings.

Elite HRV (a mainstay in the HRV-tracking space) had this to say about why its app doesn’t yet support using the Apple Watch for HRV data:

The latest versions of Apple Watch now produce an “HRV” value that is primarily intended for the Apple “Breathe” app. The raw data behind these “HRV” values are not available for analysis and, to the best of our knowledge, are is not intended for calculating RMSSD, LnRMSSD, HF, LF or other trended HRV values.

To be sure, if you are moving your hand, wrist or arm at all, then there is a very low degree of confidence in the accuracy of the HRV calculations that could be produced from the Apple Watch at this time. Even if perfectly still, there are many circumstantial variables to address such as sensor positioning, skin contact, skin thickness/color, emitter spectrum, etc. Until the raw R-R interval data or full pulse waveform data is available for analysis, we will not be able to verify one way or the other.

Marco Altini, creator of HRV4Training, had similar things to say about why their app doesn’t support the Apple Watch’s metrics:

In HRV4Training we use rMSSD as it is well established that it is a marker of parasympathetic activity, and therefore the lower the value, the higher the level of stress, relative to your baseline / past data (obviously, an oversimplification). From a human physiology point of view, this links to the fact that parasympathetic activity is mainly the activity of the vagus nerve. The vagus nerve acts on receptors signaling nodes to modulate pulse on a beat to beat basis while sympathetic activity has different pathways with slower signaling hence beat to beat changes reflect parasympathetic activity and can be quantified using rMSSD or HF (see Nunan et al.).

Unfortunately Health right now does not allow developers to write features other than SDNN, because that is what the Apple Watch computes and reports. As Apple has been improving Health and the Watch in the past few months, hopefully more HRV features will also be added in the future.

It may well be that Apple is currently only interested in HRV tracking to help users with the Breathe app, or that it doesn’t yet think the Apple Watch hardware is accurate enough to give deeper-dive measurements, but I’m excited to see it in the Health app nonetheless — it’s a good start from Apple at tracking one of the more-fascinating wellness statistics out there, and I hope we see them add more HRV values as time goes on.

Other apps and devices that calculate HRV

If you want more information than simple HRV averages, there are several other apps that can take and analyze HRV, but you may need to pick up an external heart monitor to use them effectively.

The friendliest app out there for HRV tracking that I’ve found is Welltory; it breaks down your HRV results into easily-readable areas like Performance (which represents your average HRV), Energy (how your parasympathetic function is working), and Stress (same for the sympathetic). For basic measurements, you don’t even need a proper passive electric chest strap — you can use your iPhone’s rear camera instead (though this may produce a higher margin of error).

The app is free to use for these basic measurements; upgrade to a paid subscription, however, and you can access more detailed measurements from your HRV calculation (including your LF/HF, VLF, SDNN, and more).

It’s worth noting given all the privacy and political concerns of late that Welltory began as a Russian startup. That said, it’s currently based out of NY and has a pretty straight-forward privacy policy. Given that the data is analyzed on Welltory’s servers, however, I wanted to mention it.

HRV4Training also lets you use either your iPhone’s rear camera or an external heart monitor to measure your HRV, but the $8.99 app is designed specifically for the athletic crowd: It tracks the same metrics as Welltory, but uses a 30-day rolling scale to provide suggestions about your baseline and how you should train from day to day. (It is a little buggy on the UI side when running on my iPhone X, but I’m not sure if that’s the iPhone model or the app as a whole at fault.)

The aforementioned Elite HRV app has a ton of scientific data behind it and many happy users, but you’ll need an external heart rate monitor and a $4.99 in-app purchase to take full advantage of it. The app’s UI also hasn’t yet been updated for iPhone X.

The $13.99 SweetBeat HRV uses slightly different formulas than Elite HRV, but has the same pros (happy users, lots of data) and cons (older, requires a chest strap, out of date app).

I tried but was unimpressed by Alex Olsson’s $3.99 HRV Score, which uses your Apple Watch to track HRV measurements; unfortunately, I couldn’t get the app to take a reading without crashing.

More on HRV

Want to read more about HRV? Here are some more in-depth resources that talk about the science behind it, formulas, and some suggestions on how to use it.

  • What Is Heart Rate Variability And What You Can Learn From It
  • Heart Rate Variability 101
  • Heart Rate Variability: a (deep) primer
  • Everything You Need To Know About Heart Rate Variability Testing
  • A Deep Dive Into HRV: The Myths & Truths of Heart Rate Variability Testing

Blog Index

How To
1. Intro to HRV
​2. How to use HRV, the basics
3. HRV guided training
​4. The big picture
​5. HRV and training load
​6. HRV, strength & power
7. Overview in HRV4Training Pro​
8. HRV in team sports

HRV Measurements
Best Practices
1. Context & Time of the Day
2. Duration
​3. Paced breathing
4. Orthostatic Test
5. Slides HRV overview
6. Normal values and historical data

Data Analysis
1a. Acute Changes in HRV
(individual level)
1b. Acute Changes in HRV (population level)
​1c. Acute Changes in HRV & measurement consistency
1d. Acute Changes in HRV in endurance and power sports​
2a. Interpreting HRV Trends
2​b. HRV Baseline Trends & CV
3. ​Tags & Correlations​
4. Ectopic beats & motion artifacts
5. HRV4Training Insights
6. HRV4Training & Sports Science
7. HRV & fitness / training load
​8. HRV & performance
9. VO2max models
10. Repeated HRV measurements
11. VO2max and performance
12. HR, HRV and performance
13. Training intensity & performance​
14. Publication: VO2max & running performance
​15. Estimating running performance
16. Coefficient of Variation
17. More on CV and the big picture
​​​​​18. Case study marathon training
19. Case study injury and lifestyle stress
20. HRV and menstrual cycle
21. Cardiac decoupling
22. FTP, lactate threshold, half and full marathon time estimates
​23. Training Monotony

Camera & Sensors
1. ECG vs Polar & Mio Alpha
2a. Camera vs Polar
2b. Camera vs Polar iOS10
2c. iPhone 7+ vs Polar
2d. Comparison of PPG sensors
3. Camera measurement guidelines
4. Validation paper
​5. Android camera vs Chest strap
​6. Scosche Rhythm24
​7. Apple Watch
8. CorSense
​9. Samsung Galaxy

App Features
​1. Features and Recovery Points
2. Daily advice
3. HRV4Training insights
4. Sleep tracking
5. Training load analysis
​6a. Integration with Strava
6b. Integration with TrainingPeaks
6c. Integration with SportTracks
6d. Integration with Genetrainer
​6e. Integration with Apple Health
​​6f. Integration with Todays Plan
7. Acute HRV changes by sport
8. Remote tags in HRV4T Coach
9. VO2max Estimation
​10. Acute stressors analysis
11. Training Polarization
​12. Lactate Threshold Estimation
13. Functional Threshold Power(FTP) Estimation for cyclists
14. Aerobic Endurance analysis
15. Intervals Analysis
​​​16. Training Planning
17. Integration with Oura
18. Aerobic efficiency and cardiac decoupling

1. HRV normal values​
​2. HRV normalization by HR
​3. HRV 101

  1. Flatt AA, and Esco MR. Validity of the ithleteTM Smart Phone Application for Determining Ultra-Short-Term Heart Rate Variability. Journal of Human Kinetics volume 39/2013, 85-92.
  1. Heathers JAJ. Smartphone-enabled pulse rate variability: An alternative 2 methodology for the collection of heart rate variability in 3 psychophysiological research. Int J Psychophysiol. 2013 Sep;89(3):297-304.
  1. Aubert AE, Seps B, and Beckers F. (2003). Heart Rate Variability in Athletes. Sports Med 2003; 33 (12): 889-919.
  1. Bellenger CR, Fuller JT, Thomson RL, Davison K, Robertson EY, Buckley JD. Monitoring Athletic Training Status Through Autonomic Heart Rate Regulation: A Systematic Review and Meta-Analysis. Sports Med, Ahead of Print.
  1. Bigger JT Jr; Fleiss JL; Steinman RC; Rolnitzky LM; Kleiger RE; Rottman JN. (1992). “Frequency domain measures of heart period variability and mortality after myocardial infarction”. Circulation. 85 (1): 164–171.
  1. Kleiger RE, Miller JP, Bigger JT Jr, Moss AJ (1987). “Decreased heart rate variability and its association with increased mortality after acute myocardial infarction”. Am J Cardiol. 59 (4): 256–262.
  1. Bilchick KC, Fetics B, Djoukeng R, Fisher SG, Fletcher RD, Singh SN, Nevo E, Berger RD. Prognostic value of heart rate variability in chronic congestive heart failure (Veterans Affairs’ Survival Trial of Antiarrhythmic Therapy in Congestive Heart Failure). Am J Cardiol. 2002 Jul 1;90(1):24-8.
  1. Pagani M. Heart rate variability and autonomic diabetic neuropathy. Diabetes Nutr Metab. 2000 Dec;13(6):341-6.
  1. Agelink MW, Boz C, Ullrich H, Andrich J. Relationship between major depression and heart rate variability. Clinical consequences and implications for anti-depressive treatment. Psychiatry Res. 2002 Dec 15;113(1-2):139-49.
  1. Cornelissen, VA, Vanhaecke J, Aubert AE, Fagard RH. Heart rate variability after heart transplantation: A 10-year longitudinal follow-up study. Journal of Cardiology Volume 59, Issue 2, March 2012, Pages 220–224.
  1. Tortora, G.J., and Derrickson, B.H. (2009). Principles of Anatomy and Physiology. Volume 1, 12th ed. John Wiley & Sons: Asia.
  1. Vandeput, S, Taelman J Spaepen A, and Van Huffel S. Heart Rate Variability as a Tool to Distinguish Periods of Physical and Mental Stress in a Laboratory Environment.
  1. Dong GJ. The role of heart rate variability in sports physiology. Exp Ther Med. 2016 May; 11(5): 1531–1536.
  1. Hjortskov N, Risse´n D, Blangsted AK, Fallentin N, Lundberg U, Søgaard K. The effect of mental stress on heart rate variability and blood pressure during computer work. Eur J Appl Physiol (2004) 92: 84–89.
  1. Weise, F. et al. (1986) Acute alcohol ingestion reduces heart rate variability. Drug & Alcohol Dependence, 17(1): 89-91.
  1. Aubert AE, Seps B, Beckers F. Heart rate variability in athletes. Sports Med. 2003;33(12):889-919.
  1. Ross, C. What’s at the heart of breakdowns? Equus;May 2008, Issue 368, p46.
  1. Giles D, Draper N, Neil W. Validity of the Polar V800 heart rate monitor to measure RR intervals at rest. Eur J Appl Physiol. 2016; 116: 563–571.
  1. Sookan, T. Heart rate variability in physically active individuals: reliability and gender characteristics. Cardiovasc J Afr. 2012 Mar; 23(2): 67–72.
  1. Warren JH, Jaffe RS, Wraa CE, Stebbins CL. Effect of autonomic blockade on power spectrum of heart rate variability during exercise. Am J Physiol. 1997 Aug;273(2 Pt 2):R495-502.
  1. Cottin F, Papelier Y, Escourrou P. Effects of exercise load and breathing frequency on heart rate and blood pressure variability during dynamic exercise. Int J Sports Med. 1999 May;20(4):232-8.
  1. McNarry MA, Mackintosh KA. Reproducibility of Heart Rate Variability Indices in Children with Cystic Fibrosis. PLoS One. 2016 Mar 11;11(3):e0151464.
  1. Winsley RJ, Armstrong N, Bywater K, Fawkner SG. Reliability of heart rate variability measures at rest and during light exercise in children. Br J Sports Med. 2003 Dec;37(6):550-2.
  1. Leicht AS, Allen GD. Moderate-term reproducibility of heart rate variability during rest and light to moderate exercise in children. Braz J Med Biol Res. 2008 Jul;41(7):627-33.
  1. Esco MR and Flatt AA. Ultra-short-term heart rate variability indexes at rest and post-exercise in athletes: evaluating the agreement with accepted recommendations. J Sports Sci Med 13: 535-541, 2014.
  1. Flatt AA and Esco MR. Heart rate variability stabilization in athletes: towards more convenient data acquisition. Clin Physiol Funct Imaging In Press, 2015.
  1. Esco MR, Flatt AA, Wellborn B, Nakamura NY. Agreement between a smart-phone pulse sensor application and ECG for determining lnRMSSD. J Strength Cond Res. 2016.
  1. Flatt AA, Esco MR, Nakamura FY, Plews DJ. Interpreting daily heart rate variability changes in collegiate female soccer players. J Sports Med Phys Fitness. 2016 Mar 11.

What Exactly Is Heart Rate Variability Training?

If you haven’t heard of heart rate variability training, it’s worth it to your workouts to learn a bit more.

It seems like heart rate variability is the next big thing in wearable fitness data—and there’s good reason for the hype.

With hyper-accurate detection of the time between heartbeats, HRV monitors and corresponding training apps (like Aaptiv) open up a new world of possibilities for intuitive training—one that’s informed by your physical state, not the other way around.

Here to explain how to make the data work for you is Simon Wegerif, director of ithlete, an app that tracks heart rate variability.

Why Monitoring Heart Rate Variability Matters

Knowing and monitoring your resting heart rate (we LOVE this device) is generally good health advice. But it’s only part of the story your ticker has to tell.

“Counter to what you might expect, your heart is actually not beating with a metronomic regularity,” Wegerif says. “In fact, variability in the heart rate is very healthy.”

That’s because the variability in your heart rate reflects the current state of your body. The more variability, the better your physical condition, Wegerif explains.

“If your body is very stressed, then there’s very little variability in beat-to-beat heart rate,” he says. “But if your body is relaxed and aerobically fit and healthy, then you’ll get a lot of variability from your heart rate.”

Therefore, the heart’s ability to vary the duration of time between beats is indicative of its ability to reflect changes in the rest of the body.

That means you’re ready to work. If your exercise schedule involves HIIT routines, for instance, a high variability reading in the morning means you’re clear to crush the gym.

It doesn’t mean that your condition can’t change later in the day, though.

“With convenient HRV monitoring, you’re taking a snapshot of the autonomic nervous system, which is basically valleyed for the time you’re taking the snapshot,” Wegerif says.

A stressful day at work may alter your heart rate variability before a post-work run or gym session. So factor the day’s impact on your body into your morning variability metric.

How Heart Rate Variability Integrates Into Your Training

Professional athletes use heart rate variability to schedule workouts around high variability readings and rest players who have low variability.

Wegerif says one English Premier League team orders a medical inquiry for players with unexplained drops in heart rate variability.

But most of us don’t have the time to schedule around a daily readout. Still, this method affords users the ability to push the envelope with confidence.

Athletes who periodize their training (such as a marathoner in a base-building phase) do so knowing they’ll go into periods of constant low energy due to the high training load.

Such phases are a gamble. Go hard and win fitness, but go too hard and risk burnout or illness.

“Endurance athletes are known for being very hard on themselves, and there’s a danger of nonfunctional overreaching,” Wegerif says.

It’s hard to tell whether overreaching is functional (in that it ultimately elevates your fitness) or nonfunctional while you’re doing it.

But monitoring your HRV means you’ll know when you’re healthy enough to stay on the gas. You’ll also know when you’re running on fumes.

HRV apps do the work for you.

Rather than leave you to interpret the figures, HRV apps, such as Wegerif’s, set parameters within a designated amount of standard deviations from your baseline reading.

The baseline is essentially a moving average of your daily HRV snapshots from a period of weeks, Wegerif explains.

“We give people a green light as long as they’re within an acceptable range around their baseline,” he says. “Then, of course, they can still choose the workout they want to do that day.”

A yellow reading on Wegerif’s app indicates subpar recovery and suggests a rest, and a red reading means you should probably skip the day’s workout.

Over a period of weeks and months, improvements in cardiovascular fitness will move the baseline HRV up, reflecting improvements in overall health.

What else can heart rate variability predict?

HRV is a reflection of the overall load on your body. Therefore, an unexplained low variability may be indicative of an impending illness—perhaps one brought on by a high training load.

Take one of Aaptiv’s meditation classes to relax your body and mind.

“On the road toward overtraining, you weaken the immune system. So you make yourself more likely to contract upper respiratory infections, coughs, and colds,” Wegerif says.

Carefully monitoring heart rate variability while attempting to hold constant life’s variables—changes to diet, sleep, work, and exercise—can tell us a lot about how our bodies react to certain stimuli.

But the technique does have limits. One misconception is that HRV can tell you how your gut feels about the sandwich you ate for lunch.

“ is sensitive to hydration status and the state of the digestive system,” Wegerif says. “There a lot of conflicting things going on when the digestive system is mobilized.”

Start Training with Heart Rate Variability

You’ll need to download an HRV app and connect it to a heart rate monitor (like this best seller). Not all monitors are created equal, and your smartwatch isn’t going to be as accurate as a purpose-built device.

“EKG is the gold standard for measuring HRV,” Wegerif says. “You’re measuring the time between every heartbeat very precisely, to a resolution of about two out of 1,000 milliseconds. It’s really quite an accurate measurement.”

In order to get reliable data, a chest-mounted or fingertip heart rate monitor with EKG technology (such as this device) is your best bet. Although, Wegerif says developments in wearable-enabled clothing with sewn-in sensors also looks promising.

Apple claims the company is developing EKG technology small enough for the Apple Watch.

However, the current model, along with the rest of the wrist-mounted wearable market, sacrifice accuracy for size.

They use photoplethysmography to take snapshots of the autonomic nervous system. However, they rely on algorithms that are susceptible to motion and changes in the amount of blood in the skin at the time of measurement.

A less accurate measurement means your metric could read more standard deviations from the baseline than it actually is. So keep that in mind if you’re not using an EKG-enabled device.

Be Consistent

Take your measurement at the same time each morning, Wegerif advises, and do it first thing. You’re allowed to use the bathroom, but that’s it.

Eating or drinking beforehand throws off the reading, as does stress. “You need to do it without checking a bunch of tweets or anything that would give you mental stress,” he says.

Particularly fit people will want to take the reading standing up. A strong parasympathetic vagal tone interferes with a reading taken from a supine position, Wegerif explains.

Using an app that charts HRV over weeks and months, examine your training peaks and valleys. Employ the data to empower smarter training cycles.

“Try to get a little bit scientific with it,” Wegerif says. “Try changing one thing at a time, and see what you learn about yourself.

To get your heart rate up, look no further than the workouts from Aaptiv. Check out the newest classes we’ve just added to the app!

Heart Rate Variability: The New Science of Recovery

Heart rate variability is an indicator of how well the parasympathetic nervous system functions. It provides athletes with a powerful measure of both their recovery and their ability to function well in an upcoming workout.

READ MORE: Heart Rate Variability a Good Intensity Measure

The Sympathetic and Parasympathetic Nervous Systems

The autonomic nervous system is made up of two components: the sympathetic and parasympathetic systems:

  • The sympathetic nervous system is similar to a gas pedal in a car. When we press the gas pedal, more gas is pumped into the engine, which allows us to go faster or apply more torque. Similarly, when our sympathetic system ramps up, our heart pumps out more blood to allow for more nutrients to feed the muscles.
  • The parasympathetic system can be likened to the brakes in a car. We want a responsive braking system. We don’t want to have jerky brakes that lock up or brakes that don’t engage enough.

As we are building our perfect machine, we want to have a good acceleration system, as well as an optimal system to slow ourselves down. If we think about taking fast curves in our car, we need sensitive and responsive brakes to allow for the fastest possible driving of the curves. The parasympathetic system is our brakes.

The Vagus Nerve Controls the Systems

The vagus nerve innervates many different organs. One branch of our vagus nerve (our brakes) slows down heart rate. As we inhale, that branch of our vagus nerve is inhibited (so our brakes are not responsive), which allows our sympathetic system (our gas) to run free. As we exhale, our vagus nerve inhibitory action returns and our heart rate slows down.8 This mechanism is probably one of the reasons for the benefits of meditative breathing.3,7

What Is Vagal Tone and Heart Rate Variability?

Vagal tone is a general term for the responsiveness of our braking system. There are multiple ways to measure it. One of the most precise ways is to measure respiration and heart rate. We can then calculate the effect of the vagal nerve on heart rate (called respiratory sinus arrhythmia).

“Athletes can now measure heart rate variability outside the lab by measuring heart rate and having an app do relatively complex calculations.”

This calculation is pretty complicated as it is taking different waveforms and transforming them to a measure of vagal power. The problem with this method is that we need to take into account respiration. In our lab, we can connect people for an hour-long study with around seven sensors to get an accurate of picture of heart rate and respiration. In the real world, this application is not practical. Luckily, we can skip measuring respiration and still get a pretty accurate account of vagal tone with just a heart rate monitor.

The change in heart rate, or heart rate variability, gives us a simple way to measure how well our parasympathetic system works. More variation in our heart rate is indicative of greater parasympathetic activity. Athletes can now measure heart rate variability outside the lab by measuring heart rate and having an app do relatively complex calculations. This measurement is inexpensive and accurate – if you follow some simple rules.

Equipment for Measuring Heart Rate

A look through the Google Play store or the App Store will reveal hundreds of apps that have something to do with heart rate variability. At Breaking Muscle, we have two reviews of complete systems, BioForce HRV and iThlete. Both of these systems have free apps, but you must purchase the heart monitoring system through their websites. The nice part of these apps is that you get the complete package and both provide information tailored for athletes.

“I suggest you measure right after waking. It only takes about two minutes and it provides a great excuse to stay in bed a little longer.”

Another option is to purchase (or use an existing) heart rate monitor band and a compatible app. I use My HRV beta as my app (sorry, only for Android) and a compatible Polar heart rate monitor (total cost around $50). I am also testing another potentially good heart rate variability app, Elite HRV, which is available for both Android and Apple products.

Elite HRV Dashboard

Important Issues in Monitoring Heart Rate Variability

The time of day, substances ingested, movement, and mood are all important variables in measuring heart rate variability. I suggest you measure right after waking. It only takes about two minutes and it provides a great excuse to stay in bed a little longer.

Here is my routine:

  1. After waking, put on the heart rate monitor band.
  2. Start the app, lay back, and let it run for about two minutes (two minutes or more gives an adequate amount of data for the algorithms to process; shorter times may not be as accurate).

It will take a few days before the numbers will become meaningful. I would take notes on your workouts to see the correlations between your numbers and how you feel. The numbers are related to you and are not useful unless you can compare it to your previous data (furthermore, different apps use different algorithms, so the numbers between apps will be different, as well). Some apps provide guidance on your ability to perform. I would use those as rough rules of thumb, but rely mostly on your numbers relative to previous numbers.

RELATED: Heart Rate Monitoring: An Effective Test for Overtraining

Why You Should Care About Heart Rate Variability

Many different health outcomes are associated with poor heart rate variability including diabetes, obesity, hypertension, and other cardiovascular diseases.2,10 For athletes, there seems to be a reciprocal relationship that exercise (anerobic and aerobic) increases heart rate variability and that heart rate variability is a good indicator of exercise performance.1,4,6,9 In a recent study with judo athletes, monitoring heart variability was useful for determining athletes’ stress and recovery from earlier workouts.5 So, as far as indicators of overtraining, the most important factor for you to consider might be heart rate variability.

RELATED: Eat, Drink, and Be Healthy: How to Fuel Your Performance


Heart rate variability is a relatively simple measure that athletes can use to test how well they are recovering. Recent mobile technology lets us monitor our heart rate variability in our homes and relatively inexpensively. As recovery is a vital component of our continued progress, it make sense to measure it. The better we eat, sleep, and reduce stress, then the better our heart rate variability, and hence our recovery.

1. Aubert, AE., et al. 2003. “Heart Rate Variability in Athletes.” Sports Medicine 33 (12): 889–919.

4. Furlan, R., et al. 1993. “Early and Late Effects of Exercise and Athletic Training on Neural Mechanisms Controlling Heart Rate.” Cardiovascular Research 27 (3): 482–88.

5. Morales, J, et al. 2013. “The Use of Heart Rate Variability in Monitoring Stress and Recovery in Judo Athletes.” Journal of Strength and Conditioning Research, November, 1. doi:10.1519/JSC.0000000000000328.

6. Mourot, L., et al. 2004. “Decrease in Heart Rate Variability with Overtraining: Assessment by the Poincaré Plot Analysis.” Clinical Physiology and Functional Imaging 24 (1): 10–18.

7. Nesvold, A. “Increased Heart Rate Variability during Nondirective Meditation.” European Journal of Cardiovascular Prevention & Rehabilitation, June. doi:10.1177/1741826711414625.

8. Porges, SW. 2007. “A Phylogenetic Journey through the Vague and Ambiguous Xth Cranial Nerve: A Commentary on Contemporary Heart Rate Variability Research.” Biological Psychology 74 (2): 301–7. doi:10.1016/j.biopsycho.2006.08.007.

9. Sacknoff, DM.1994. “Effect of Athletic Training on Heart Rate Variability.” American Heart Journal 127 (5): 1275–78.

Photos 1 & 4 courtesy of .

Photo 3 courtesy of Elite HRV.

Heart rate variability fitness

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