A DEEPER DIVE INTO HRV...

If you’ve read my first blog post on heart rate variability (The ABC’s of HRV) then you will understand what I’m talking about when I say that HRV measurements provide a window of insight into the autonomic nervous system - the system that controls whether the body is in a state of ‘fight or flight’ (known as ‘sympathetic’ drive) or ‘rest and digest’ (known as ‘parasympathetic’ drive).

As we move throughout our day to day life, we continuously transition between these two states. Our happy baseline is more towards the parasympathetic state, and we can think of our sympathetic drive like a dial which can be turned up when we are under stress or pressure, helping us gear up to go. This results in physiological changes such as an increased heart rate and blood pressure, dilation of the pupils in the eyes, and changes in the relative areas of blood distribution around the body. From an evolutionary standpoint, these changes are necessary to allow us to hunt, escape danger, and fight. The two branches of the nervous system work as opposites to one another, and when the stress or threat has passed, the sympathetic control dial is turned down and we can resume a more restorative parasympathetic state.

 When in this state of rest and relaxation, our heart rate is closely linked to our breathing - known as ‘respiratory sinus arrhythmia’. This is what HRV scores reflect. When we breathe in, our heart rate speeds up slightly, and when we breathe out, it slows down. In a sympathetic dominance, our heart rate typically beats faster, and the coherence between our breathing and heart rate decreases (as does our HRV score). So for the most part, a ‘good’ HRV score occurs when there is increased variability between heart beats. This seems counter-intuitive at first, but it indicates our tendency towards this rested, non-stressed state, where the heart is beating a bit slower and this coherence exists with our breathing rate. It’s interesting to note that we can also directly influence our HRV score through this same mechanism - by manipulating our breathing rate, we can slow the heart rate and alter our autonomic control more towards a state of rest and recovery. This is the reason that slowed breathing can help calm you down - you are literally slowing down your heart rate!

Through regular HRV measurements every day, we start to identify where our baseline level is, and any deviations that occur above or below this baseline level. This is hugely valuable as it allows us to connect the dots between the stresses that we are exposing our body to - exercise, lack of sleep, poor diet, alcohol consumption, dehydration, illness, as well as emotional stresses (work, relationships) - and the consequences that they have on our body and recovery. HRV also allows us to track changes occurring over time, so that we can see the impact that positive lifestyle changes are having on our overall health.

In a nutshell, a drop in HRV typically demonstrates that the sympathetic / ‘fight or flight’ dial has been turned up, over-riding the parasympathetic activity and hindering the body’s ability to relax and recover. This is the body’s response to stress. In the case of training adaptations, it is normal (and necessary!) to expose your body to physical stresses sometimes in order to improve. In fact, we specifically want to push ourselves towards this state a few times a week in order to improve our performance. Too much time in this zone without adequate recovery may result in over-training however, and eventual declines in performance. For fatigue management, we typically don’t want to spend too much time in this sympathetic zone, so our exercise and activity programs are designed accordingly.

An acute increase in HRV is generally a good thing and may occur after a particularly restful sleep or after doing activities such as diaphragmatic breathing / meditation which help to improve this synchronicity between the heart rate and breathing. The caveat to this is that sudden, sharp increases in HRV (when following on from low / sympathetic dominance scores) can actually indicate the body going into a forced ‘shut down’ in order to deal with the accumulated stress. Constantly being in parasympathetic drive isn’t ideal either, as you will likely just end up feeling lethargic! As with many things in life, it all comes down to striking the right balance.

Lucky for us, the Elite HRV app takes out a lot of the interpretation work by analyzing all of your data relative to your baseline and providing your with a ‘Morning Readiness’ score, and recommendations for the day. These scores are either green (good to go), yellow (take caution), or red (prioritize rest and recovery).

As you can imagine, this data is hugely valuable when it comes to monitoring the effects of an exercise program for clinical populations affected by fatigue, such as cancer, chronic fatigue, fibromyalgia, and post- concussion. I am also developing a strong interest in to its application for mental health conditions such as anxiety and depression, where fluctuations in HRV readings may help people to anticipate and understand their day to day changes in symptom severity. (This field of science is known as psycho-physiology and it really highlights the mind-body connection! A big area of interest for me).

I personally have found that the data gained from daily HRV scores have been an accurate representation of my physical state. Most weeks I tend to have 2-3 days dipping into the yellow zone following on from accumulated training loads of sessions at the gym and busy work days. During this Level 3 lock-down period however, I’ve had Green scores every day! While lock down laziness tempts me with extended sleep ins, there’s no hiding from the data telling me that I am physiologically primed to get up and go!