In the last 4 weeks I have been doing a lot of research when it comes to HRV, along any research I have been doing I have also been tracking my own so that I have experience of exactly how this works. I use an app called Elite HRV and just the last two weeks the new Apple watch. With the Elite HRV app I have been using a H10 Polar chest strap. I do this every single morning as soon as I wake up.
What Is Heart Rate Variability (HRV)?
A healthy heart beat contains healthy irregularities. Even if your heart rate is, say, 60 beats per minute, that doesn’t mean that your heart beats once every second or at one second intervals like a clock.
Rather, there is variation among the intervals between your heartbeats. The interval between your successive heartbeats can be, for example, 0.85 seconds between some two succeeding beats and 1.35 seconds between some other two.
Even though the difference is measured in parts of seconds, you can actually feel the difference.
Here’s a tip for anyone who wants to experience it: place a finger gently on your neck or wrist and find your pulse. You should feel that the longest intervals take place when you exhale, and the shortest intervals when you inhale.
How you calculate heart rate variability depends on what technology you use. Using an ECG, or electrocardiogram, it’s typically the R peak in the QRS complex that marks a heartbeat. Hence, the intervals between heartbeats are called R-R intervals.
With the H10 Polar heart strap, the Orthostatic Test is a test that monitors the training-induced changes in the function of your autonomic nervous system. It measures your heart rate and RR intervals both at rest and standing up and displays these values as a result in the Elite HRV App.
There are many factors that affect the results of the Orthostatic Test, such as mental stress, sleep, latent illness and environmental changes (temperature, altitude) to mention a few.
Changes in heart rate and HRV are always individual, and this is why you should do the test regularly to establish your individual baseline. To make sure that your results are as reliable as possible, you need to perform the test in similar conditions every time.
I do mine every morning, I get up, have a shower, brush my teeth and after that I lay in bed and do the 2 minute test, breathing normally.
Once you have your baseline set, you can start following the results. the Elite HRV app shows you your average heart rate and HRV values, and if they are slowly increasing over time, you’re probably making steady progress in your training. Sudden deviations from the averages could signify that something is off-balance.
DEFINING HEART RATE VARIABILITY
Heart Rate Variability is a measure which indicates the variation in your heartbeats within a specific timeframe. The unit of measurement is milliseconds (ms).
If the intervals between your heartbeats are rather constant, your HRV is low.If their length variates, your HRV is high.
There are different ways to calculate HRV, but they all have to do with the amount of variation in the intervals between heartbeats. The most commonly used HRV formula is rMSSD (Root Mean Square of the Successive Differences).
The figure below is an example of interbeat intervals in milliseconds.
Why Is Heart Rate Variability an Important Measure?
To understand HRV, we first need to understand our nervous system and heart rate. Heart rate variability can be traced back to our autonomic nervous system.
The autonomic nervous system regulates very important systems in our body, including heart and respiration rate and digestion. The autonomic nervous system has a parasympathetic (rest) and a sympathetic (activation) branch. Heart rate variability is an indicator that both branches are functioning – the parasympathetic in particular.
Intrinsic heart rate is measured in the condition in which neither parasympathetic nor sympathetic regulation is present. When completely blocked from autonomic regulation, a healthy heart contracts at a rate of about 100 beats per minute (the number is individual, however).
Parasympathetic regulation lowers your heart rate from the intrinsic level, giving more room for variability between successive heartbeats. Parasympathetic regulation causes almost immediate changes that affect only a few beats at a time, after which the heart rate returns towards the intrinsic rate. Sympathetic regulation elevates your heart rate from the intrinsic level, and there is less room for variability between successive heartbeats. Sympathetic regulation affects several consecutive heart beats.
Put these together and we can formulate a rule that when the rest-related parasympathetic branch is active and the sympathetic branch is inactive, your heart rate is lower and HRV higher. Factors such as stress can lead to the withdrawal of parasympathetic activity, or activation of sympathetic branch even when you are resting, both leading to elevated heart rate and lowered HRV.
HRV AND CARDIOVASCULAR TRAINING
Heart rate variability has been studied, for example, in the context of cardiovascular training.