Heart Rate Variability (HRV)
I’m due for the write up on the follow up article for the ‘Knee Osteoarthritis’ piece but since I’m currently finishing up the presentation for the upcoming RC Coaching Training Camp at Langkawi (for the preparation of Ironman Langkawi 2019 in a couple of months’ time) entitled ‘Optimizing Recovery Methods for the Endurance Athlete’, I’m going to do a short write up on one of the methods of monitoring recovery…the Heart Rate Variability (HRV).
In the good old days (ie when I first started running and racing in 2008), the usual method for monitoring one’s state of recovery was Resting Heart Rate.
It was simple and it made sense.
Every morning when you wake up, you take your pulse (be it from your radial pulse or from your carotid pulse – or wherever you can regularly find your own pulse) for an entire minute and take note of the number.
The fitter you are, the lower this number will be.
After measuring this on a regular basis for a bit, you should more or less know how high (or low) your resting heart rate should be.
In times of stress (increasing training load, one too many high intensity workouts, inadequate sleep, boss giving you hell for the past few days etc) you will find that your resting heart rate goes up slightly. That tells you that you need to take a couple of easy days during training or even a few days off.
But as with advancement in wearable technologies such Garmin watches, Fitbits, Apple watches (my personal favourite at the moment) and a variety of fitness trackers, we (the athletes) become more data driven and dependent. Born out of this drive for more data to track our training, performance, recovery and perhaps give us a sense of control, is the science of Heart Rate Variability (HRV).
So…what is Heart Rate Variability (HRV)?
Our heart rate is usually measured within a minute, and calculated as ‘beats per minute’. However from heart beat to the subsequent heart beat, there is a rate of change to it…or what is called, variability. Medically, we call this Sinus Cardiac Rhythm. Most medical personnel will tell you that beat to beat, there is a small minute irregular change and that it is absolutely normal.
Of course having said that, when this beat to beat variability becomes very huge, then it will be categorized as ‘irregular heart beat’ or scientifically as ‘Arrhythmias’. But this is an entirely different topic than the one we started off with.
Back to HRV.
So…the greater the beat to beat variability, then the HRV is high.
If the beat to beat variability is low, then the HRV is low.
High HRV is suppose to reflect more parasympathetic activation in the body while low HRV is the opposite, where there is more sympathetic activation.
Now I’m going to drop a bit more science bomb on you.
What is parasympathetic and sympathetic activation….and what does that mean for you as an endurance athlete?
Ever heard of ‘Fight or Flight Response’?
That pretty much sums up sympathetic vs parasympathetic system.
They are both the Autonomic Nervous System (ANS) which means it controls the part of your nervous system which to most degree you have little control over but it functions to keep you alive!
For example….you may not be much of a sprinter in real life. You run too little (or not at all) to want to call yourself a runner and walking up a flight of stairs will likely leave you gasping for air and weak in the knees. However one day as you walk to your car that was parked pretty far (perhaps a kilometer away) from where you are, you notice a rabid stray dog barking madly and running towards you. From the looks of things, dog had gone out of its mind and most likely things will not end up well for you if this dog gets to you. You are panicking, hyper alert as you look around to see if there is any chance of someone to help you. Unfortunately you are alone (hypothetically). Your heart rate goes up and you are sweating. Without much hesitation, you turn the other way and RUN! All you can think about is that you do not want to get bitten by this rabid dog and you must flee (pun intended).
You run for several minutes and you finally get to your car. You rummage your pockets for your car keys to get out of harm’s way. You turn back to see how far this crazy dog is from you….when you realize the dog is nowhere in sight. Then you realized that you just sprinted a good kilometer at 4:00 pace.
That…is what the sympathetic nervous system is for in a rather exaggerated story telling manner.
(I also suggest getting yourself checked by an optometrist or a shrink about the non existent dog)
The parasympathetic nervous system on the other hand, does the exact opposite. It calms you down, slows down your heart rate and breathing rate. Helps with your digestion and probably does a whole lot of good in getting you to sleep deeper and more restfully.
So tying this back with the HRV, the higher the HRV reading reflects more PARAsympathetic activation which aids in your recovery from training.
Too much sympathetic stimulation will not be good for your general health outside of training and racing as it will affect your digestion, your sleep, riles up your anxiety and probably edges your blood pressure and blood sugar on the higher end.
By monitoring your HRV on a regular (more or less daily) basis, you get a sense of where you are on this ANS spectrum (are you more sympathetic or parasympathetic?) and taken that into account with your training load, allows you to rate whether you are recovering well or over reaching in your training.
By the way, over reaching is a normal response to training stimuli. You over reach then recover adequately for improvement in performance. However over reach for too long and NOT recovery, you will fall into the abyss of over training which may take a very VERY long time to bounce back from (that it a whole different topic altogether) .
So now that we understand regarding HRV and how it represents our ANS, let’s discuss about some of the methods of measuring our HRV.
Our smart phones have quite a few apps for measuring HRV….all with different pros and cons. Few months ago, I took it on myself to do an experiment of n=1 (which means only 1 research participant), where I downloaded 3 different HRV apps on my phone and measured my HRV every single morning upon waking up on all 3 apps.
The apps that I utilized for this experiment were (1) HRV4training, (2) ithlete and (3) Elite HRV.
(you can find these on the Apple App Store or the Google Play Store)
Elite HRV and ithlete Pro needed me to have a Heart Rate Monitor (HRM) with Bluetooth function so it is detectable on my phone.
Only HRV4training does the measurements using Photoplethysmography (PPG) where I place my finger over the camera of the phone and it measures my heart beat for a duration of 1 minute. It is the same technology that the newer Garmins (and other sport watches) and fitness tracker (like my Apple watch) use where heart rate is measured from your wrist.
The portability and ease of use is definitely better on the HRV4training but I dislike the idea of PPG measurements because the accuracy of measurement depends on how steady you place your finger over the phone camera (I can attest that despite not having hand tremors, I am usually very groggy in the morning and have difficulty keeping my finger still over the camera lens).
As for ithlete Pro, it syncs with Training Peaks and churns out a lot of data and graphs which is perfect for those Type A athletes who LOVES these sort of data and nicely produced graphs. I personally know A LOT of these sort of people. You need a Bluetooth HRM and it measures for a total duration of 1 minute. However, this app is always overly optimistic despite the fact that I feel like shit after heavy leg day at the gym or after a long run on some hilly route because someone wanted good pictures of the KL skyline on a Sunday morning. But again, this is THE perfect HRV app for the Type As who LOVES to train and go hard day in and day out. But it also makes me question how reliable this app is in preventing the athlete from pushing themselves into overtraining.
(I read a few forums regarding this app and noted that many people did the same experiment with a variety of app-combo and concluded that this app was indeed overly optimistic)
My personal favourite would be the Elite HRV app. Yes it takes longer to give you daily data…the measurement duration is 2 minutes but from my readings, the longer the duration of reading, the more accurate the reading is. In fact there are some measurement methods that need a minimum of 5 minutes to properly measure the HRV. I would have accidentally fell asleep again if I had to measure for 5 minutes. But 2 minutes was a good in between. I felt this app was the most realistic out of the 3…where it does report that I’m edging into more sympathetic zone after heavy deadlift day or that I’m well into the parasympathetic zone where I strive to be, after my Zwift Active Recovery Zone 1-2 rides. It also has a breathing meditation function which I occasionally use (meditation and breathing exercises are 2 well researched areas that brings about more parasympathetic activation in your ANS).
“But doc…how good in predicting recovery is this HRV nonsense?”
Proponents for HRV will often sing its praises and throw out some bias research data while opposing factions will do the exact opposite and also argue that we are relying too much on our wearable technologies.
But in my opinion after being the only participant in this experiment and tying it with my training log, it is not as easy as just measuring the HRV and saying I’m good to go. Some days the HRV reading is going to be bad but I feel physically really good and training session was amazing whereas other days HRV reading is very high but I feel rather worn down and training doesn’t seem to go my way.
Playing my own Devil’s Advocate, I feel that your own perceived fatigue should take precedence over where you are at recovery wise, compared to what a number or rating on an app shows. But having said that, I also believe in collecting long term data and jotting down your own feedback with each training session because that gives you (your coach or whoever that looks at your Training Peaks) better insight into your response to training loads and sessions, that ultimately gives you (or your coach) the opportunity to adjust your training as per necessary.
And yes…I’m also a Type A Personality Athlete who LOVES data.