Everyones’ looking for an edge in life. More energy, faster recovery, improved immune function, higher performance.
One the most important ways to improve these things is to measure progress. Track what you’re doing and see what works… and of course what doesn’t.
Tweak and change to optimise results.
As the saying goes ‘ If you can’t measure it, you can’t manage it’.
So while we’re taking our supplements, experimenting with new diets and mixing up our training programs, how do we truely know whats helping us and what’s not?
Fortunately, every second of the day our body is telling us about our state of health. With every heart beat our body transmits a signal informing, whoever wants to listen, the current state of our nervous system. This signal reveals whether the body is under a state of stress, in need of recovery, in balance and much much more.
Even better, when you look at this data over time, you can start to see a larger story. Trends, patterns and cycles all emerge. Daily, weekly and monthly fluctuations show how the body is coping with the food, exercise and stress we throw at it.
Doctors can look at this data and predict whether an individual is at higher risk for health factors.
Coaches can easily see how stressed their client truely is.
Athletes can determine if their training load is too much or loo little, whether they need to taper down for an upcoming competition, or keep charging on.
All of this information is revealed every time our heart beats. It’s free. It’s easy to measure. And many of us completely ignore it.
And no I’m not referring to our pulse. I’m referring to our Heart Rate Variability.
Heart Rate Variability (or HRV going forward) is defined in Wikipedia as:
Heart rate variability (HRV) is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the beat-to-beat interval.
It is literally the variation in time between heart beats.
The time between heart beats fluctuates with every beat. Not by much, we’re only talking micro-seconds here, but there is a variability. Even at rest, someone with a heart rate of 60bpm would suggest that your heart beats at a 1 second interval right?
Upon closer inspection, it would be shown that the interval between beats is not a consistent interval. It varies. There may be a 1.1 second interval between beat 1 and 2. Then a 0.95 second interval between beat 2 and 3. Followed by a 0.93 second interval between beat 3 and 4.
Of course, if you’re counting your beats per minute over 60 seconds, these fluctuations will wash out. You will see an average.
Meanwhile it’s extremely hard for a human to detect these variations in heart beats without special technology, of which I will cover later in this article.
So now we know this variation between beats exists, what exactly does it mean?
Your HRV data can be used to show your current state of parasympathetic (rest & digest) or sympathetic (flight or fight) dominance. HRV has been used for decades to track the health & recovery of patients.
Low HRV scores are linked to higher risk of coronary heart disease (1, 2). Low HRV numbers are also indicative of depression (2), diabetes and high blood pressure (3)
Researchers are finding that regular monitoring of HRV can be useful to track health and screen for individuals at risk to serious health issues (5, 6).
A 2016 paper titled Heart Rate Variability in Breast Cancer Survivors After the First Year of Treatments: A Case-Controlled Study remarked:
HRV … could be a clinically useful tool to detect cardiovascular disease in early-stage breast cancer survivors.’ (8)
Meanwhile high HRV numbers are associated with superior cognitive function (4,7) and good vagal tone.
Athletes also benefit from regular HRV monitoring. Studies have show that tracking HRV trends can be beneficial when determining training intensity for program design (9) and can help show when someone is entering an overtrained state (10)
Current HRV tracking devices determined HRV using a electrocardiogram (ECG) device. This would pick up the electrical pulsing from the heart contraction. From this data, HRV could be determined.
This is regarded as the gold standard of HRV tracking. But just because it’s accurate for, doesn’t mean it’s a practical way to measure HRV.
To measure your HRV with ECG technology, it used to require complex machines and electrodes over the body. But with the advent of advanced heart rate monitors such as the Polar H7 heart rate strap, it meant tracking HRV from the comfort of your home was now possible.
Although a great improvement, there was still an issue around accuracy and reliability of the data.
Measurement devices such as the Polar H7 required the user to put on a Heart Rate strap, ensure it was reading the data correctly and that this data was being sent to a device to interpret the data (i.e. a smart phone). Then you needed technology (software like Elite HRV) to analyse this data.
Having used a Polar strap with my iPhone to track HRV for the past 5 years, I know there were often issues connectivity (both from the polar reading my heart rate, and the polar transmitting to the iPhone).
Sometimes it would take me 5 minutes to get a stable connection going - during which time I would get rather annoyed (and I’m sure this negatively impacted my HRV).
Other issues arose around the consistency of the HRV measurement. Because you were only measuring a ‘snap shot’, it was important that you measured your HRV at the same time, in the same position, in the same state every day.
For example. I would usually measure my HRV while laying in bed. But some mornings I would desperately need to pee, so I would get up and pee and then go back and measure my HRV. This minor activity would impact my HRV numbers,
Other mornings I would simply forget to take the reading… so I’d do it after I had been up for 30minutes moving around.
Other days I would have to get up earlier due to an early call or a flight, this of course would disrupt my routine and break the consistency habits that HRV ideally calls for.
I just lived with this, I knew the trends in HRV changes would wash out over time, and not to get too caught up in the day to day fluctuations.
The downside of all this was of course uncertainty around the quality of the data. Rubbish in, rubbish out. Even though I personally understood how powerful HRV tracking was, I would often wonder if the day to day swings were really applicable to my life.
I explained this in a lot more detail on a Podcast that you can listen to below:
However I continued tracking my daily HRV numbers, despite this limitation. I figured the swings would wash out in the long term, and I’d still get valuable information from the HRV trends.
This was the same logic I applied to my coaching clients. Don’t get too caught up with the day to day fluctuations, just focus on the longer term trends and cycles.
Jason Moore from HRV Course.com has written a great article on this titled The 8 Biggest Mistakes Made When Measuring Heart Rate Variability
Thankfully, there is now a new way to measure your HRV. And this new technology and device eliminates the concerns around consistent tracking and only getting ‘snap shots’ of data.
The new method of measuring HRV doesn’t use ECG, instead it uses an optical sensor that measures inter-beat-intervals. This is called Photoplethysmography (PPG).
PPG is an optical technique used to detect blood volume changes in the microvascular bed of tissue. Effectively it measures blood movement at the skin surface.
The great thing about this technology is it doesn’t require electrodes or heart rate straps. Nor is it invasive in anyway. And best of all, it’s just as accurate.
A 2013 study titled How accurate is pulse rate variability as an estimate of heart rate variability? A review on studies comparing PCG technology with an ECG (11) found that measuring HRV optically produced results in agreement with traditional ECG monitoring.
Though there were two minor drawbacks.
One was that activity caused inaccuracies in HRV recordings when using the PPG method. But this shouldn’t bother most users who want to track HRV. Why? Because you should measure your HRV is while you’re stationary at rest (i.e. first thing in the morning laying in bed).
Secondly, the way PPG measures HRV is slightly different to the ECG method. With an ECG device, the time between beats is measured through electrical spikes from the heart. This is referred to as ‘RR intervals’.
However with PPG, the sensor is measuring blood volume pulse near the skins surface. As a result the ‘peaks and troughs’ are smoother than the ECG readings. Factors such as arterial stiffness can impact this reading. Hence why activity and intense movement or stress could potentially lead to an inaccurate HRV reading.
Schematic illustration of ECG and PPG signals over three heart cycles. One RR-interval and IBI (inter-beat-interval) are marked with horizontal bars. Source: ŌURA and heart rate variability
But, despite these minor drawbacks, there is a big upside of PPG that allows users to get extremely accurate HRV data over an extended period of time. Which in turn allows the user to know more about their current state of health.
It allows the user to accurately measure their HRV during the night. While they sleep. Without external factors that could influence the reading.
Let me explain..
I’ve spent many mornings wishing there was a way to streamline the HRV recording process. Wishing I could simply wake up in the morning and have my HRV data without having to put on a heart rate strap and lay in bed counting the minutes go by.
I created a mental check list of the perfect HRV measurement system.
Well very recently I found a solution to my problems. It was literally right under my nose, or in front of my nose depending where my hand was at the time.
You see I had been wearing a high tech wearable called an Oura Ring. I predominantly used this to track my sleep (as it’s extremely accurate as discussed here). As it had some other neat in built features like activity tracking and a recovery score, I ended up using this ring beyond my sleep tracking. I was using it for life tracking!
For those who have followed me on social media you may have seen this ring pop up in pictures a few times. But if you want to learn more about the Oura Ring, have a read of my (rather lengthy) review here The One Wearable To Rule Them All? Oura Ring Review.
Anyway, I knew the Oura Ring had a way to measure HRV, but I didn’t understand how this was done, and most importantly there was no way to access this data. As great as the ring was, I was still having to track my HRV with a Polar heart rate strap every morning.
Then I got the news. The team at Oura had just released an update to their Oura app. The new update displayed your overnight HRV average!
Wondering how the ring was tracking HRV, I did some research. That is when I learnt about PPG technology and optical inter-beat-interval measurement. This little ring was literally measuring my HRV every night I went to bed. And now I could finally access this data!
The Oura Ring, with it’s new software update was now the perfect way for me (and everyone else) to track my heart rate variability. Here’s why.
The longer the recording, the more reliable the data is. Which helps the user make more informed decisions about their health, training and recovery.
Anyone who has tracked their HRV using a polar heart strap know’s how tedious it can be. Laying still for 5 minutes every morning while you take a reading of your heart beats.
That’s if the app you use even takes a 5 minute reading, most apps by default only take a short 1 minute reading.
We want accurate, reliable data, but it mean putting on a heart rate strap and laying still for at least 5 minutes every morning of the week…
Sure you could leave the heart rate strap on while sleeping and try and get an overnight reading, but this created issues with connection reliability (the strap has to stay in constant communication with the iPhone), measurement problems (if the strap moves during the nigh you may not get an accurate signal from the heart), battery costs (8 hours a night, every night a week is going to mean lots of batteries!) and finally the nnEMF issue (the strap uses Bluetooth, and your phone must also have bluetooth enabled. You’re radiating your body, your heart, for 8 hours a night..).
But with the combination of the new PPG measuring technology and the Oura Ring practically living on your finger, it was now possible to accurately measure your heart rate variability over extended periods without worrying about battery issues, nnEMF issues or poor readings.
Even better comparison of the OURA rings HRV data was compared to a ECG device (The Faros 360 ECG device with Kubios HRV software to be precise). The results of the study found a near perfect correlation between the two devices. The coefficient of correlation was 98.4% (13).
Not too shabby considering the ECG device is specifically designed to measure HRV and retails for over a $1000usd. (The Oura costs a fraction of this. Plus you can get a 10% off discount code HERE).
I had finally found the perfect way to measure my HRV!
As I mentioned above, with the Oura Ring update, the app now displayed your daily HRV reading (which was an overnight average).
You simply synced your Oura Ring to your phone, and the data was displayed. When you synced your ring to see your sleep data, you could now see your HRV data under the Readiness tab.
Plus, with the new Oura Cloud platform, you now have access to even more data. You can literally see your HRV data over night while sleeping.
The phone app gives you the overnight average and your trends, but the cloud platform gives you a full breakdown of your overnight HRV data.
And with the recent Oura Cloud updates (learn more here) you can now compare this HRV data to other metrics that the Oura is tracking (such as activity, deep sleep, body temperature etc).
By now we know that:
But what do we do with all of this data now that we have it?
Data needs meaning for it to be useful information.
Thankfully, with the Oura Cloud platform it’s now easy to turn these daily HRV numbers into meaningful information.
You can easily see when your HRV has dipped, or increased. How it correlated to other metrics (such as sleep, or training) and how external factors may have influenced your HRV (for example a new diet you started, or a holiday you went on).
For athletes, you can use this HRV trend data to determine how hard to push in training. Whether to continue on your current program or mix it up. Or even how far out to taper for a race. We know that low HRV numbers are indicative of declining health, too high of a stress load and overtraining. Now we have a tool that easily (and accurately) measures this data, but also displays these trends for us to utilise.
As I mentioned earlier, being able to compare the HRV data with other metrics is extremely useable.
You can now use your body temperature data from my temperature tracking log and compare it to your HRV. Or how that new healthy mattress you brought impacted your HRV. Or how your sleep quality impacts HRV.
This is actually another reason why the Oura Ring is such a neat device. It tracks all this for you - it’s tracking body temperature, sleep quality, movement, resting heart rate, respiration rate and now of course HRV.
So if you’re eager to learn more about your body, to gain in edge in life, and to tap into the information our heart is telling us then be sure to track your HRV.
And if you’re sick of putting on a Polar Heart Rate strap every morning to track your HRV, look into the Oura Ring. It has literally saved me 35minutes a week!
13. The HRV of the Ring – Comparison of nocturnal HR and HRV between ŌURA and ECG Kinnunen Hannu O. 1,2), Koskimäki Heli 1,3), 1) ŌURA health, Oulu, Finland, 2) University of Oulu, Electrical Engineering, Finland 3) University of Oulu, Biomimetics and Intelligent Systems Group, Finland
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