Researchers at Harvard University have gone as far as to say that measuring your Heart Rate Variability is “a visual insight into the most primitive part of your brain” which sounds great but how can us fit folks use it to our advantage?
What Is HRV?
OK, enough beating around the bush. Time to talk about HRV seeing as it is the current reigning champion in the realm of quantifying athletic recovery.
HRV is simply a measure of the variation in time between each heartbeat. This variation is controlled by a part of the nervous system called the autonomic nervous system (ANS). It works regardless of our desire and regulates, among other things, our heart rate, blood pressure, breathing, and digestion.
A healthy heart does not tick along like a metronome. The oscillations and variations of a healthy heart are complex and non-linear. A healthy heart’s beat-to-beat fluctuations are often described as “mathematical chaos.” The variability of what scientists call non-linear systems is said to provide the flexibility our biology needs to rapidly cope with uncertain and changing environments. So, while a healthy biological system exhibits complexity, impaired biology can involve either a loss or an unhealthy increase in complexity.
In an oversimplified nutshell, let's say your heart rate is 60bpm. With a healthy HRV, each beat is separated by a wide range of milliseconds. With an unhealthy HRV, the beat to beat variability is drastically lower, and a 60bpm heart rate would show an unchanging beat every second. Like a stopwatch versus a jazz drummer.
The healthier your nervous system the faster you are able to switch gears.
The reason for this is that the brain is constantly processing information in a region called the hypothalamus. The hypothalamus, through the ANS, sends signals to the rest of the body to either stimulate or relax different bodily functions. It responds not only to a poor night of sleep or getting yelled at by your boss, but also to the exciting news that you got a raise or to that yummy burrito you ate for lunch.
But, if we have very regular stress, unhealthy diet, poor sleep, dysfunctional relationships, feelings of isolation or solitude, and lack of exercise, this balance may be disrupted and your fight-or-flight response can kick itself up a notch.
As we discussed earlier, the status of your nervous system is an important indicator of your body’s training response. Nervous system measurements can indicate your response to training, and Heart Rate Variability is considered to be a view inside the nervous system.
How Your Heart Works
The origin of your heartbeat is located in what is called a node of your heart. If you are alive, your SA node (sino-atrial) will generate a certain number of electrical impulses per minute, which directly impacts how many times your heart will beat per minute. Easy, right?
Your SA node activity, heart rate, and rhythm are largely under the control of your autonomic nervous system, which is split into two branches, the “rest and digest” parasympathetic nervous system and the “fight and flight” sympathetic nervous system.
When you are well rested and haven’t been training excessively your parasympathetic and your sympathetic nervous system play well together and produce responses in your heart rate variability to respiration, temperature, blood pressure, stress, and more. And as a result, you tend to have consistent and high HRV values.
If you are not well rested, the healthy beat-to-beat variation in your heartbeat begins to diminish and a consistently low HRV value, or HRV values that tend to jump around a lot from day-to-day, indicate an imbalance.
In a strength or speed athlete, or someone who is overdoing things from an intensity standpoint, we often see more sympathetic nervous system overtraining, and a highly variable HRV (a heart rate variability number that bounces around from day to day). With endurance athletes we generally see more parasympathetic nervous system overtraining and a consistently low HRV value. You can read more about that in a study called Decrease in heart rate variability with overtraining.