What is Heart Rate Variability?
Heart rate variability (HRV) is the variation or difference in the gap between one heartbeat and the next. When we think of our heart rate, we usually think of 60–90 beats per minute (bpm), which is the range for an average heart rate. This number is an average of the speed of your heart rate over one minute; your heart rate actually changes from beat to beat, speeding up when you inhale, and slowing down upon exhale. A pulse of 60 bpm will be an average of a heart rate over a minute that could vary between 55 and 66 bpm. Unlike a clock that ticks at a constant rate, the bio-electric beat of the human heart is constantly changing.
With high levels of HRV, a person experiences lower levels of stress and greater resilience. Low levels of HRV are an indication of heightened stress and lower resilience. HRV is closely linked to physical, emotional, and mental function, mediated by our nervous system and our breathing.
This variability is an adaptive quality in a healthy body. HRV as a naturally occurring regularity in the heart rate has been shown by many years of clinical research to indicate levels of stress and the resilience (flexibility, adaptability) of the nervous system. With high levels of HRV, a person experiences lower levels of stress and greater resilience. Low levels of HRV are an indication of heightened stress and lower resilience. HRV is closely linked to physical, emotional, and mental function, mediated by our nervous system and our breathing. The more flexible we (and our nervous system) are, the more we can cope with life’s inevitable stressors. HRV is a measure of this flexibility.
Stress and Our Stress Response
We all experience stress from time to time caused by both the outside world and inside our heads – intensive jobs, studies, family responsibilities, finances, body consciousness, social pressures – the list is exhaustive! Some of us will deal with stress more effectively, and others might recover from stressful events quicker and easier. Being stressed all the time can lead to coping behaviours, which help to alleviate stress, such as anxiety, anger, depression, comfort eating, chronic exercising, drinking – you get the point. Quick fixes that provide some form of relief but have negative side-effects or qualities.
One of the clever systems in our bodies is called the nervous system. This is what mediates our perception of the outside world, and facilitates how we consciously and unconsciously react to the environment. There are two arms of the autonomic nervous system (ANS): the sympathetic nervous system, and the parasympathetic nervous system, which together govern many of the body’s automatic internal processes. The sympathetic increases the heart rate, while the parasympathetic decreases the heart rate. Think of them as the accelerator pedal (sympathetic) and the brake pedal (parasympathetic) of a car. The balance between these two systems creates a dynamic but orderly increase and decrease in heart rate, controlled by two different electrical ‘pacemakers’ in the heart. These pacemakers are affected by a variety of inputs, which include breathing, pressure sensors in the arteries (baroreceptors), thermal regulation, and anxious thinking. Higher (healthier) HRV indicates a harmonious functioning of these two (brake and accelerator) systems together.
Let’s have a closer look at each arm of the autonomic nervous system. The sympathetic (accelerator) nervous system is also referred to as the ‘fight or flight’ response. Imagine you’re a caveman, and a mountain lion is approaching; your flight or flight response is what will allow you to notice the danger, react, and get yourself out of the situation. It is a state of hyperarousal that primes you for fighting or fleeing. Your body releases adrenaline and cortisol (stress hormones), your heart rate rises, and the thinking part of your brain (neocortex) is shut down as instinct takes over for the escape. This is the accelerator pedal slammed to the ground.
Low HRV is associated with a higher risk of death in patients with heart disease and in the elderly, and with a higher risk of coronary heart disease in the general population. Low HRV is also linked to hypertension, diabetes, and chronic obstructive pulmonary disease.
We don’t have to run away from lions too often these days, but our body doesn’t know that. An argument with your partner or a confrontation with your boss at work is perceived by your body in the same way – DANGER! You get the same stress response in these modern-day situations as our ancestors would have done, yet we rarely need that same level of arousal in response. Furthermore, we tend to come across many little ‘stressors’ throughout the day – little stimuli that cause this stress response to be activated chronically – meaning many of us are in this fight or flight mode most of the time. This is not good considering the fight or flight reaction can increase blood pressure and blood sugar and suppress the immune system, digestion, and cognition. Together, these help make a little more sense of the reactions we often get during periods of stress: difficulty concentrating, an upset stomach, becoming run down and ill. Keeping the accelerator pedal slammed down is going to wear the car out, drain the fuel tank, and even lead to a crash!
The parasympathetic (brake) nervous system controls sleeping, relaxing, digestion, urinating, defecating, and sexual arousal and is the counter to the sympathetic/fight or flight system, often referred to as ‘rest and digest’. This is the state you should be in most of the time, especially when going to sleep, digesting food, or any other physiological function that isn’t extreme muscular contraction! This is taking the foot off the accelerator and gently applying the brakes.
Understanding the difference between how your body feels when it is in either of the two states (accelerate or brake), and what is going on inside your body is really important. Chronic stress simply leads to your body not being able to carry out many functions that are vital to survive and thrive. Being able to think clearly, to fight off infections, to properly digest your food, and to be properly sexually aroused are main features of being in a parasympathetic state and learning how to put yourself into this state is hugely useful. Here’s how HRV can help.
How Does HRV Relate to Stress?
Low HRV is a sign of stress and stress directly acts upon the autonomic nervous system (accelerator vs brake) creating an imbalance, lowering HRV. Low HRV is associated with a higher risk of death in patients with heart disease and in the elderly, and with a higher risk of coronary heart disease in the general population.1 Low HRV is also linked to hypertension2, diabetes3, and chronic obstructive pulmonary disease4. When the system is in balance, HRV is higher. High HRV is a sign of resilience. A resilient nervous system is a sign that you can flexibly adapt to the changing environment.
Luckily, we can train ourselves to increase our HRV levels. The autonomic nervous system is not normally under conscious control, but this can be changed. Using a mixture of technology and consciously effected techniques, you can override the stress response, increasing your HRV and putting you back into that parasympathetic state – that rest and digest mode. These techniques involve conscious breathing, meditative-type exercises, physical relaxation, and positive visualisation. The technology includes heart rate monitors and sensors, which can be strapped around the chest or on the earlobes. These provide biofeedback that allow you to see in real-time the state that your nervous system is in and how the various techniques affect your HRV. You can train yourself to recognise the different feelings of low and high HRV and how to change yourself from low to high; from accelerate to brake. This is immensely powerful in building resilience to stress, and with daily practice can change you from being controlled by stress to being in control.
HRV and Exercise
Another cool way that you can use HRV measurements is in deciding whether to workout or to recover. Using the Sweetbeatlife App (there are others too), you take a daily measurement of your HRV when you wake up, using a heart rate monitor. After recording a baseline for a week, the app will analyse changes in your HRV and recommend to either carry on training as usual, have a low exertion workout, or have a recovery day. It measures how well your body is recovering from exercise through HRV and how stressed your nervous system. This is used by elite athletes and performers around the world, and should be considered by everyone engaged in high levels of activity who want to enhance their recovery and generally protect their bodies through smart training.
What Can We Take Away From All of This?
- HRV is a measure of stress and resilience of our nervous system.
- Low HRV is bad, high HRV is good.
- You can consciously increase your HRV (and lower your stress) using techniques and technology (often together).
- HRV for performance allows you to tailor your recovery from workout for maximum health of your nervous system, performance, and workout recovery.
How Can You Measure and Train your HRV?
Sweetbeatlife App – mobile app and heart rate monitor. Measures HRV for stress, performance training, and workout recovery. It also has functionality for measuring food intolerances.
How do you rate your recovery from stress? Have you ever measured your HRV? Leave a comment below to let us know your stress management techniques.
- Dekker, J. M., Crow, R. S., Folsom, A. R., Hannan, P. J., Liao, D., Swenne, C. A., & Schouten, E. G. (2000). Low heart rate variability in a 2-minute rhythm strip predicts risk of coronary heart disease and mortality from several causes: the ARIC Study. Atherosclerosis Risk in Communities. Circulation, 102(11), 1239–1244.
- Weber, C. S., Thayer, J. F., Rudat, M., Sharma, A. M., Perschel, F. H., Buchholz, K., & Deter, H. C. (2008). Salt-sensitive men show reduced heart rate variability, lower norepinephrine and enhanced cortisol during mental stress. Journal of Human Hypertension, 22(6), 423–431.
- Seyd, P. T. A., Ahamed, V. I. T., Jacob, J., & Joseph, P. K. (2008). Time and frequency domain analysis of heart rate variability and their correlations in diabetes mellitus. International Journal of Biological and Life Sciences, 4(1), 24–27.
- Stein, P. K., Nelson, P., Rottman, J. N., Howard, D., Ward, S. M., Kleiger, R. E., & Senior, R. M. (1998). Heart rate variability reflects severity of COPD in PiZ α1-Antitrypsin deficiency. Chest, 113(2), 327–333.