Heart Rate Variability (HRV) has lately been increasingly popular in the scientific world and also often mentioned in the press. In Sweden the coach for the national U21 football team used it in mental training during Euro 15, a tournament that the Swedes ended up winning. There is a lot of debate regarding the scientific evidence for using it in mental training, but most people agree on it’s validity when it comes to heart disease and depression. This is a brief summary of what it is and a look at the recent research on what it can and can’t do.
What is it
HRV is the small variation in timing between two heartbeats. Even though you have a resting heart rate of 60, if you look closely on the timing between all two beats, the rate can easily vary between 50-70 over a minute. Normally, we count the number of beats in a minute, but with HRV we try to look closer and measure the exact timing in microseconds between two heartbeats. If we measure 3-4 of these timings in a row, and we see a big variation in the time between the heartbeats, we say that we have a high HRV. Simple as that. Oh, and before we go deeper, and you already want to start measuring, know this: It’s generally considered good to have a high HRV. Now, why do these micro variations happen?
Why it happens
Why do you get a heart beat at all? The heart needs an electrical impulse, and this is continuously given from a group of cells called the Sinoatrial node, which is a small blob of cells located in the top right part of the heart. Let’s call it the Heart Beat Blob. The Heart Beat Blob sends out impulses to the heart all the time demanding it to produce heartbeats at a rate of around 100-120 beats per minute at rest. But not all impulses are turned into heartbeats, which is why we have a significantly lower resting pulse as a healthy person (usually it’s around 50-70 bpm). What keeps it down is a branch of our nervous system called the Autonomous Nervous System, which is the part of our nervous system that we don’t directly control with our conscious mind. It keeps everything in the body going, such as heartbeats and breathing and we don’t have to do a thing. Like an autopilot. Let’s call it the Autopilot Nervous System.
So, the Autopilot Nervous System is the gatekeeper that – among lots of other things – allows the impulses from the Heart Beat Blob to pass through and make heartbeats. This Autopilot is split into two branches: The Sympathetic and Parasympathetic branch. The Sympathetic branch is the part that kicks in when something is happening and we need to be alert, like when we see a lion coming against us or playing an important football game, or – unfortunately – going on a date. This branch wants to keep us active and alert, and is doing that by increasing heart rate, breathing rate, blood pressure etc, a typical overachiever behavior. The other side of the story, the parasympathetic branch of the autopilot does the exact opposite and should be mostly activated when we are at rest. He’s the slacker guy that might not always get a lot of things done, but he is really nice to be around. These two opposites of the autopilot nervous system, the Overachiever and the Slacker, are both always active and are constantly balancing against each other, and this balance determines what is happening in the body, including how to handle the Heart Beat Blob.
Now to the actual question, why is HRV happening. There are actually two reasons. When we are breathing in, there is a mechanism in the body that turns down the influence from the Slacker, and hence increases the influence from the Overachiever. This means that your heart rate is increasing when breathing in, due to this shift in the Autopilot Nervous System, and this phenomenon is know as Respiratory Sinus Arrhythmia. Arrhythmia sounds bad, but this is something totally normal. However, since our heart rate now is varying with our breath, this means that our variability in heart rate is increasing, right? And if we are calm and at rest, the Slacker side of the Autopilot Nervous system is in charge, and that means that there are more of this Slacker influence to turn down, which in turn gives higher variations in heart beat. Got it? On the other hand, if the Overachiever is in charge and we are breathing in, there is not a lot of Slacker influence to turn down, so the heart rate is not changing that much. But if the Slacker is in charge, there is a lot of Slacker influence to turn down, and the heart rate varies a lot. So, if your Slacker part of the Autopilot Nervous System is in charge, you will have more variation in your heart rate due to your breathing, and therefor a higher HRV. The conclusion: If you are calm and rested, you will have a higher HRV than if you are stressed and on edge.
I said there were two reasons that we have a HRV, and the other reason is a bit more complex. Its called Mayer Waves and is related to micro variations in blood pressure, which are also connected to the Autopilot Nervous System and especially the Overachiever branch. However, the connections between the Respiratory Sinus Arrhythmia and these Mayer Waves are quite complex, and honestly we don’t need to go that deep to continue with this article. Let’s call them Forget We Mentioned It Waves.
What is says, and if it can be used in a wellbeing study like My Quantified Mood
The million dollar question: What conclusions can we draw from measuring HRV values? If we look into the scientific literature, there is quite a lot of evidence for HRV to be a predict things like:
- Sports physiology1
- Sudden cardiac death2
- Headache disease3
…and possibly wellbeing? Well, it’s pretty well researched that being in a constant state of stress is bad for you. So if you measure your HRV when you are in a normal state for a couple of days, and in that way sets a baseline for your normal HRV level, you can use that baseline to see you current relative state on any given day. If you on a day have very low HRV compared to baseline, you know you have a dominance from mr Overachiever in the Autopilot Nervous System. And whilst this might be okay for a day or two when you really have to be on your toes to perform well, being in that state for a long time is depleting your resources since you are not getting enough rest. On the other hand, if the HRV is high compared to baseline, you know the Slacker is in charge, and this mean your body is signaling that you are in a state of recovery. Then on some days, you are perfectly on your baseline, which means you have a balanced body (at least regarding your Autopilot Nervous System).
But then we have the other claims, such as Håkan Erikson, coach for the Swedish U21 football team, who used “HRV training” to improve the mental balance in his players. There are so many questions mark in that sentence I am embarrassed to have written it, but my guess is that they were trained in controlled breathing, which is a well known meditation technique calming the body (putting the Slacker in charge), and then using HRV to measure the effects. So HRV is not the real tool here, just the measurement of what is happening.
And what does the research say? There are results4 showing that HRV is decreased in persons with depression and bipolar disease, indicating that it could be a measurement of wellbeing. However, the article stresses that more studies has to be made in order to draw conclusions regarding cause and effect. Another review article5 claims that low HRV is connected with clinical depression, but then only if the person has recently had a heart attack.
And, my favorite, the article “A Heart and A Mind: Self-distancing Facilitates the Association Between Heart Rate Variability, and Wise Reasoning”6 claims to have found a connection between high HRV and the the ability to reason in a wise way.
So, it seems like there might be som really cool connections between high HRV and wellbeing factors, but more research has to be done to really prove that. Personally this evidence is more than enough for me personally, that a high HRV at least isn’t bad. Yea, I even conclude that it’s good. And if you want to reap the benefits of this and increase your HRV, is there a way? Some research7 suggests that yoga is a way of doing this, but you guessed it: they conclude that more research is needed.
- Dong, J. (2016). The role of heart rate variability in sports physiology (Review). Experimental and Therapeutic Medicine, 11, 1531-1536.
- Niemeijer, M.N, van den Berg, M.E, Eijgelsheim, M, van Herpen, G, Stricker, B.H.Ch, Kors, J.A, & Rijnbeek, P.R. (2014). Short-term QT variability markers for the prediction of ventricular arrhythmias and sudden cardiac death: A systematic review. Heart, 100(23), 1831–1836.
- , , , and Vagally mediated heart rate variability in headache patients—a systematic review and meta-analysis Cephalalgia 0333102415583989 36(3):265-78
- Bassett D. A literature review of heart rate variability in depressive and bipolar disorders. Aust N Z J Psychiatry. 2015;
- Harris, P. R., Sommargren, C. E., Stein, P. K., Fung, G. L., & Drew, B. J. (2014). Heart rate variability measurement and clinical depression in acute coronary syndrome patients: narrative review of recent literature. Neuropsychiatric Disease and Treatment, 10, 1335–1347
- A Heart and A Mind: Self-distancing Facilitates the Association Between Heart Rate Variability, and Wise Reasoning” by Grossmann I, Sahdra BK and Ciarrochi J (2016)
- Paul Posadzki, Adrian Kuzdzal, Myeong Soo Lee, Edzard Ernst, Yoga for Heart Rate Variability: A Systematic Review and Meta-analysis of Randomized Clinical Trials. Applied Psychophysiology and Biofeedback , Volume 40, Issue 3, pp 239-249