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Everything You Need to Know About Heart Rate Variability
Heart Rate Variability – or simply HRV – is said to be an indicator which can be used to monitor overall health, biological age, aerobic fitness and levels of stress. HRV has recently become a popular metric among biohackers and fitness fanatics, especially as technological advances now make it possible to measure at home.
What is Heart Rate Variability?
Heart Rate Variability – or simply HRV – is said to be an indicator which can be used to monitor overall health, biological age, aerobic fitness and levels of stress. HRV has recently become a popular metric among biohackers and fitness fanatics, especially as technological advances now make it possible to measure at home.
HRV is the difference in timing between each heartbeat interval. The variation between heartbeats is controlled by a particular part of the nervous system referred to as the Autonomic Nervous System or ANS.
What is the ANS?
The ANS controls most of our internal organ functions, such as the heart, stomach and intestines. The ANS works whether we want it to or not, that is why you don’t have to consciously decide for your stomach to digest your food.
The ANS is a critical part of our breathing, blood pressure and digestion processes. The ANS helps keep the bodies internal environment (temperature, blood sugar, oxygen etc.) in balance.
The ANS is divided into two sub-components, namely the parasympathetic and sympathetic nervous system. In layman’s terms, these are known as the relaxation response and the fight-or-flight reaction (1).
The parasympathetic nervous system
The parasympathetic system, or relaxation response, helps with the day to day tasks such as digestion, slowing the heart rate and decreasing blood pressure.
The sympathetic nervous system
The sympathetic system, or fight and flight response, prepares the body for energy output and protects it from injury. It shuts down the gut, speeds up heart rate, increases blood pressure and increases blood sugar for energy consumption.
The sympathetic system is associated with the fight or flight response.
The brain responds to stimuli in our environment and subconsciously decides whether the body should be relaxed or in a fight or flight state. The brain sends signals from the hypothalamus to the ANS to trigger these responses in the rest of the body.
A poor night’s sleep, a stressful day at work or an argument with a loved one are some examples of negative stimuli which can trigger the fight or flight response. The body is usually capable of handling negative stimuli on a day to day basis. However, if one constantly experiences too much stress and unhealthy relationships with others, this may result in an excessive fight-or-flight response.
What Does Your Heart Rate Variability Tell You?
For a regular healthy person, the heart rate variability should increase whenever they engage in relaxing activities. If that person is doing yoga, lying in bed or simply resting, their parasympathetic nervous system is in control and their HRV is high. On the contrary when stressed, the sympathetic nervous system takes control, this results in a lower HRV (2).
HRV levels naturally change in response to your day-to-day encounters and interactions. However, chronic stress can result in the sympathetic nervous system or fight or flight response being in constant control. In healthy individuals the heart is able to quickly switch between sympathetic and parasympathetic states, resulting in a high HRV, whereas people with cardiac problems, or experiencing chronic stress may show a low HRV.
Research has shown a relationship between low HRV and depression, anxiety, cardiovascular disease and an increased risk of death (3).
A low HRV could predict an early death!
How can I use HRV?
Stress tracking
Measuring HRV over a few minutes at the same time each day (e.g. upon waking) can provide you with a useful metric for monitoring stress levels. Knowing when your HRV is low can help you incorporate healthy habits into your day when they are most needed.
Activities such as mindfulness, meditation, sleep, and physical activity can all help increase HRV.
Prevent over-training
Elite athletes and trainers monitor heart rate in conjunction with HRV to conduct various tests to determine when the body is in need of rest or conversely when it is recovered and ready to train again. Conducting such tests reduces the risk of overtraining.
Many of the HRV monitoring devices and apps have such tests built in. One example is the Orthostatic Test from Polar (4).
What is a good score?
Generally a higher HRV score is an indicator of good health however it is not easy to define what constitutes a “good” score. HRV scores will change significantly for individuals depending on time of day, their position when the reading was taken and their activity levels. There are also a number of different ways to measure HRV and as yet there is no standardized approach (5).
It is therefore important to only compare HRV scores taken at similar times under similar circumstances and on the same device. For example upon waking, in a seated position and using a polar chest strap with the Welltory app.
The best way to judge your HRV is to monitor it over time. It is worth taking note of the average score when you are in periods of low stress, such as a holiday, and then comparing the readings on days after intense exercise or when you are experiencing lots of stress at work. There are a number of apps (mentioned below) which allow you to easily monitor this.
For those determined to know how they stack up against the general population we have included some stats below. These values are based upon the rMSSD method (6,7,8,9):
Young, highly trained individuals 70 - 120
Young sedentary individuals 30 - 50
In patients with chronic heart failure in the 20s
Methods of measuring Heart Rate Variability
Most devices employ one of two approaches to monitor HRV, an ECG or PPG.
ECG
An electrocardiogram (ECG) is the most accurate way to detect HRV. An ECG measures the electrical activity of the heart. This method requires electrodes to be placed directly on the chest. The electrodes require secure contact with the skin to work effectively.
PPG
Photoplethysmography (PPG) differs from an ECG in that instead of measuring the electrical activity it illuminates the skin with a small light and then measures changes in light absorption. The skins light absorption changes in response to blood pressure and blood flow, thus this can be used to monitor HRV.
While PPG can produce good results it can easily be disrupted, any motion during measurement or light pollution can result in an incorrect reading.
Recommended devices for HRV monitoring
Gone are the days when you have to be sent to the hospital just to get your HRV checked. There are now many compact and convenient devices which allow you to check you HRV whenever you want.
A chest strap which utilizes ECG technology will provide the most accurate results. Some fitness watches also claim to produce reliable HRV measures but results vary, most of these watches use PPG technology.
Recently a number of mobile phone apps have been released allowing users to measure HRV using their phone. The apps access the phones camera which uses PPG technology to measure HRV. Some companies claim these measures are accurate however there is still a lack of independent studies. When we tested these apps using both PPG via the camera and ECG using a chest strap we found the results varied significantly.
For the average user curious about HRV and interested in taking the occasional HRV reading we recommend downloading one of the apps below and using your phones camera to take a PPV reading. For the more serious enthusiast interested in monitoring HRV on a daily basis or during your exercise workout, we suggest investing in a chest strap.
Recommended mobile apps
Here are just some of the best apps when it comes to measuring and recording HRV.
Welltory
This is one of the most user-friendly HRV-measuring apps for both iPhone and Android users.
Welltory allows users to measure their HRV using the phones camera, the camera uses PPG technology to measure HRV. Welltory can also be used with a variety of chest straps and fitness watches for a more accurate measure of HRV.
Welltory also connects to a very wide range of other fitness trackers and apps. Welltory has a user friendly interface and can break down your HRV results easily and divide them into comprehensible categories. These categories include performance, energy and stress levels.
The basic version is available free however a fee is required to access to access premium features.
HRV4Training
HRV4Training is another app that you can download whether you’re on an iPhone or Android device. This app also allows you to use your phones camera to obtain a PPG reading of your HRV. For a more accurate reading the app can also be used with a chest strap to obtain an ECG reading.
It’s designed to track your metrics in 30-days and then provide training suggestions on how you can do better. Unfortunately there is no free version and the basic version starts at $9.99.
Elite HRV
Elite HRV is another free app available to both Android and iPhone devices. The main drawback is that it requires an external heart rate monitor, it will not allow you to use your phones camera to generate a PPV reading. We also found the design is not as user friendly as Welltory or HRV4Training.
The app is free for both operating systems, but to access the full feature set you need to pay $4.99.
Recommended devices
The apps Welltory and HRV4Training will allow you to take a PPG HRV reading using your phones camera. A PPG HRV reading can also be obtained using most high end fitness watches (Garmin, Polar) and even the Apple watch. For the average person a PPG reading is sufficient.
For the serious enthusiast who wants a more accurate ECG reading a chest strap is required. Below are some suggestions.
Polar H7 Bluetooth Heart Rate Sensor
Polar is an established company, well-known for its heart rate and exercise-assistive products. Their H7 Bluetooth Heart Rate Sensor can be comfortably worn on the chest and is available in two sizes. It has up to 200 hours of battery life.
The H7 uses ECG technology for a more accurate reading and is one of the more affordable HRV monitoring devices available.
Polar H10 Bluetooth Heart Rate Sensor
This is the newer model from Polar, some of the upgrades include a doubling of the battery life to 400 hours. And this model is waterproof,
so suitable for swimmers.
Garmin Premium Heart Rate Monitor
This heart rate monitoring device from Garmin measures your HRV while keeping you comfortable with its soft strap. It’s also a waterproof device so you can use it while swimming.
It can easily transmit data to any other Garmin fitness tracker or your preferred iOS or Android app.