Heart Rate Variability: Part 1
We all love to train, and train at high intensity. Of course we do, otherwise you wouldn’t be here reading this post. However everyone has good days and bad days whilst training. We’ve all been there – you get to the squat rack and load up a nice, comfortable warm-up weight and you’re left in a daze at how heavy it felt. What if you started to feel like that most training days? What if when you’ve trained all that energy, that get up and go drive, was missing?
Your nervous system could be playing a part in this constant feeling of fatigue. More specifically, the strength and flexibility (someone say 10 components of fitness?) of your nervous system to recover from life’s stressors, such as exercise, which yes, does include CrossFit. The ability to deal with this stress correctly has a huge impact on our ability to recover for the next attempt at Fran.
Everyone knows that it’s important to take rest days and to incorporate de-load weeks into their training routine, right? How many of us actually do it? What if we could track the state of our nervous system to tell us when to train hard and when to back off? This is where Heart Rate Variability (HRV) comes in. HRV is one way to identify nervous system health and is easy to use and accessible to all for relatively low expenditure.
What is HRV?
If you’re not a science-y person, you can skip down a few paragraphs to the easy-to-follow pictures explanation, or what I like to call the Shut Up and Squat version. For the rest of you, don your propeller hats and geek out.
HRV is the variation in the time intervals between heartbeats and is measured by the variation in beat-to-beat interval which, despite common belief, doesn’t beat in a perfectly uniform manner, and varies beat to beat. So rather than saying you have a fixed pulse of say 60bpm, the beat rate will actually vary between something like 55 and 65. So HRV is a measure of this naturally occurring irregularity in heart rate.
So what does this have to do with your nervous system?
Our nervous system is broken into two parts: autonomic and voluntary. We are concerned with the autonomic nervous system which controls the body’s functions such as heart rate, digestion and breathing. Within this system we have two ‘pacemakers’ or sub systems, known as the sympathetic, or ‘fight or flight’, nervous system and the para-sympathetic, or ‘rest and recovery’, nervous system. These two sub-systems are what make you feel ready to PR your deadlift or end up making you want to go home and lay in a corner after your warm-up.
HRV is an indicator of your nervous systems’ ability to respond and recover from physical or psychological stressors. In short, when the HRV levels are high, you have a robust nervous system and are able to deal with stress adequately and recover quickly, whilst a low HRV is the complete opposite. Still with me?
So in terms of training, if your HRV is high you can train as normal and hit it hard. If your HRV is low, then take a day off or keep the intensity levels down.
In relation to the para-sympathetic and sympathetic nervous systems, when you train your sympathetic nervous system kick starts a reaction to this stressor, and then an equally powerful response from the para-sympathetic system comes in when it’s time to recover and rest. This means that your nervous system is at optimal health and in balance. HRV is your tool to track your nervous system health and in turn offer reliable markers of fatigue. [While the above statement is true for the most part, there are some more deeper and technical issues hiding behind that HRV score such as frequency domains which we will delve into in Part 2.]
This was shown in a study conducted on middle distance runners who trained hard for 3 weeks followed by 1 week of de-load. The HRV score dropped dramatically during the heavy loading phase. However, this change reversed during the recovery period and actually the athletes ended up with an overall increase in HRV, showing the true importance of de-load training and this increase in ‘rest and recovery’, or para-sympathetic activity has shown to be directly correlated to VO2 max. values.
To finish Part 1, let’s look at how we can actually monitor our own HRV. There are many ways varying in cost such as Bio Force and Omega Wave at the top end, to simple apps that connect to a heart rate monitor. The app I use is called Sweet Beat, for the iPhone and iPad. The app costs around £3, and the heart rate strap and wireless adapter cost around £30-40 together. From there it’s as simple as putting on the heart rate monitor strap, start the app and let it record for 3-5 minutes. It will then churn out some graphs and a number between 0 and 100, which is your HRV score. Remember the higher the number, the better. Again there are other details and numbers recorded, and if you truly want to understand and track your nervous system, wait out for Part 2.
In summary, HRV analysis appears to be an appropriate tool to monitor the effects of physical training loads on performance and fitness. In time the hope is to use this tool to prevent over training states and help people listen to their bodies a bit more when there is a number screaming in your face saying ‘NO, don’t do a heavy thruster and pull-up couplet!’. HRV has the potential to help us be smart about training.