What is Heart Rate Variability and how to use it for performance improvement.

What is Heart Rate Variability (HRV)?

HRV is a proxy for stress. It is an overall measurement of your stress levels and encompasses physical stressors like physical workouts and nervous stressors. 

Having a quantified measure of stress is valuable to help navigate daily life, and understand when your body isn’t properly responding to stress. Widely used for about ten years in professional sports, this could make a difference in terms of helping you to manage and modulate your mental and physical training schedules.  Incorporating a HRV measurement into your morning routine is simple and I will explain tools and methods to do this. 

What sort of measurement is it?

HRV is a specific measurement derived from heartbeats. You are very likely familiar with heart rate (HR), which is the frequency of the heartbeat, i.e. the number of beats during a given time period, often measured in beats per minute (bpm). HRV refers to the regularity of the heartbeats. You can have a given stable HR of say 60 bpm, so one per second, but are these very regular exactly every second or with very slight variations? This is exactly what HRV measures. 

Image credits: wikipedia

The main HRV measurement is, technically the” root mean square of the Standard deviations” of Heartbeats (rMSSD). It’s useful to have some understanding of your measurement, and if something is giving you a HRV measurement, what is it exactly? Is it rMSSD? It is worth checking and understanding.

What drives HRV?

HRV is reflective of the balance between two aspects of your nervous system, sympathetic (high drive, let’s go, effortful) and parasympathetic (slow down, mediated by the vagus nerve). 

A naive interpretation would be to think that very regular heartbeats, e.g. a low HRV, are synonymous with a desirable state, like a high precision clock that is very regular. This is actually the opposite, very regular Heartbeats (low HRV) are a symptom of high stress and an improper balance of sympathetic and parasympathetic nervous systems.

So high values mean ‘low accumulated stress, ready to perform’ and low values ‘high stress, needs more recovery, something is not quite right. But we must move beyond ‘high is good and low is bad’. Low HRV not only is not always bad but is something you will be happy to see as a result of a training stimulus. We need to learn how to get an interpretation of our measurements and I will come back to this.

How to measure HRV

HRV changes all the time during the day, with a very big range of variation. Having a shower, eating and drinking, can drastically alter HRV, not to mention of course exercising or playing an exhausting chess game.

As a consequence, it is crucial to measure HRV always in similar, controlled circumstances, that allow us to get comparisons. You are probably already familiar with this I’m the context of weight measurement. To compare like for like, it is required to weigh yourself at the same time every day, typically just after waking up and after having emptied your bladder. If you eat a 500g meal and drink 500 ml of water, you just ‘gained’ 1kg but of course that’s not a relevant lean body mass increase. 

There are two gold standards measurements of HRV: either all throughout the night or in the morning, just after having woken up, sitting on the bed.

HRV is measured either through the electrical signals that your body produces (you need a chest heart rate monitor) or with a camera/optical sensor that looks at the blood flow (hence can measure the heartbeats). With an optical sensor, you can either have a wearable with an optical sensor (like a smart ring) or just plainly use your smartphone camera.  

Smartphone

The app Kubios HRV is free, but you need a Bluetooth chest strap heart rate monitor. They are really cheap (about 20 USD) and provide excellent measurement. The app is great and I recommend it. You can use the chest strap for your other workouts and connect it with other apps.

The app HRV4Training is fantastic. Brainchild of Marco Altini, the leading thinker in the domain of HRV measurements and interpretation. It is a one-off cost of 10 USD with no subscription. It can use various sources including your phone camera (for a lot of phones, check if your phone is supported). If you are on a budget, check your phone compatibility and pay 10 USD to buy the app. You just place your finger on the camera and it measures your pulse. It is low effort and precise. The app allows you to tag the previous day’s event (workout, sleep quality, alcohol consumption, etc) and is amazing for understanding your current measurement in context of the range of previous measurements. 

Measurement in progress with the HRV4Training app. 

Wearables: They will typically do the all-night measurement. I can’t possibly describe all smartwatches and smart rings here, please check relevant documentation. Oura ring gives you a recovery score (more on this later)  and a ‘HRV balance’ score. This is annoying, but you can download the raw data from the oura website and it has rmSSD in it. The Apple watch does HRV measurements, I think there are caveats to the night measurement, but I think it is possible to trigger a standalone HRV measurement with an apple watch or other smartwatches. 

I have measured my morning HRV. Now what?

Measure it at the same time of the day for a whole week.

I have measured my morning HRV for a whole week. Now what?

Congrats you’re on the road to making useful insights into your stress and physiology.

What is a good HRV value?

This is the most important point to understand. Different people have different baseline values of HRV and that’s mostly due to genetics. Nothing you can do about it. The exact value is irrelevant. What matters on a given day is how your HRV value compares to your usual range. It is so important i’m going to repeat it: the absolute value of HRV doesn’t matter, what matters on a given day is how that value compares to YOUR usual range. 

The art of interpreting your HRV value

First of all, you should not put all your trust into a single number. Maybe you feel awful, tired, bad night, sore muscles, but great HRV? Trust your feeling. Conversely, if you feel amazing, well rested, but a depressed HRV? Maybe still go for your workout as planned. Measurements can fail. Trust your feelings. You wouldn’t drive your car into a lake if your GPS tells you to go straight ahead. Same for any measurement relying on technology. If your HRV is low, several possibilities: maybe you had a super hard day the day before. Or maybe you’re just about to get sick (yes, HRV will show you the first signs of sickness before anything else). You MIGHT want to take it easy on that day. If your HRV is high, you might want to use the opportunity to go harder, either in the gym or in your chess training, because you have a little spare capacity to do so. 

Note that if you follow a hard structured training plan, you will see drifts in your HRV that are due to your training load, to the adaptation of your body. Here is a chart from the HRV4Training app that shows your HRV and the value in relation to the baseline.

The problem with recovery scores

Recovery scores are great because they incorporate HRV with other data, like exercise data and sleep data. But that one feature is also what makes them awful: you wash up the specific effect of stress and the specific effect of sleep by combining them together. The whole point of HRV is to have a proxy for stress. The recovery scores are useful, but a tiny bit off topic, and a compete black box. 

Recovery and sleep scores form the Oura app.

Another problem with a recovery score is that it can make you think that you should take it easy if you are tired. But maybe your training plan calls for two hard days. Maybe you need to push yourself mentally for several days in a row because that is what the competition will require. You often can’t wait for all the stars to be aligned to push yourself.  This is where a real HRV measurement gives context: How does rmSSD react after several difficult days in a row? 

I’m going to repeat it myself: you don’t want to live a live with super high recovery score. Because that would mean you never push yourself!!

HRV for chess

Welcome to the unmapped territory. Just like me you will have to look at the data and draw your own conclusion. If you want an extra edge, you have to adopt a something before it is mainstream. In 5 years everyone will use recovery scores from their wearables and the competitive advantage will be gone. HRV is a little bit understood for exercise, but a lot less for mental fatigue. Nevertheless, you are in luck because i can show you HRV measurement from a super GM (let’s call that person Player A) after a tough game of chess. 

Here is player A’s HRV measurement (chest strap + Kubios app), on a morning, fully rested.

And let’s compare with a day after player A had a very hard workout:

The HRV really tanked with rmSSD going from 91 to 55. The app shows a readiness score which is actually okay to use here because it’s not a blended score of sleep and other measurements like for the oura app. 

I’ve had player A take a HRV measurement after a long (4h30) elite classical game. 

Incredibly the HRV is fairly low, showing how much stress was the game was. What about the following morning? 

The following morning there was some recovery. It’s not like the game was as hard to recover from as a tough day of interval workout, but still a fair amount of stress on the body.

Right now I’ve just showed you measurement and not really what we did from the point of view of the performance coaching for sake of privacy and because I used his HRV measurement just as an extra data point to take into account in the context of the overall physical and chess training. 

Of course, during competition, typically you don’t want to the player to see his results. HRV4Training has functionality so that the result isn’t visible during competition time. Imagine that you wake up and feel ok, then check your oura recovery score and it’s awful: this could be a psychological drag, your mind could start believing that you’re unwell and not fit for a big fight on the board. So just go by feel during competition, or make sure only your coach can see the measurements. 

Conclusion and takeaways:

• HRV is a proxy measurement for stress.
• It is measure with chest strap + app or with camera phone + app or by wearable.
• You need to measure HRV in the same condition every morning or use a wearable that take a measurement throughout the night.
• You use the value in context of your typical range to get an idea of the remaining amount of stress. It doesn’t mean that you automatically rest on a low day and only hammer on the high days, but it’s an extra valuable to take into account. And it can serve as a warning system when you’re just about to get sick.
• Right now all the accumulated know-how is in the contect of physical sports. If you try to gauge and modulate your mental stress and load with HRV, congratulations, you are a pioneer.
• The biggest gain to be had from technology is when few of your competitors are using it. Once everyone is using it there is no more competitive advantage. All pro athletes are using it. A lot of esports athletes are using it. Very few elite chess players are using it. 
• If you like nerdy measurements, have fun. Remember that a measurement is just a number. Do trust your own feelings of fatigue and don’t put too much blind faith in a given number.