WHAT’S THE DEAL WITH HEART RATE VARIABILITY?
You might have heard the term ‘Heart Rate Variability’ thrown around in the past couple of years. With the recent advances in wearable technology, many fitness trackers and health apps have added this functionality to their list of features, such as VIIVIO, Oura Ring, and Whoop.
If you use a fitness tracker or device regularly, you’ll know that Heart Rate Variability (HRV) is one of the ways to measure stress. Generally, these devices will measure your heart rate for a minute and give you a value and then rating of how stressed you are (from low to extreme).
But what exactly is heart rate variability and how does it measure stress? Here’s a quick crash course about heart rate variability and what it means for you.
Unlike heart rate, which is a measure of how many times your heart beats in one minute, HRV measures the time between heart beats (measured in milliseconds). There are small fluctuations in time from beat to beat that are too small to feel but are an indication of a healthy heart. This is shown in the image below.
A higher variation in beat-to-beat time is indicative of low stress, whereas a low variation is indicative of high stress. This might seem counterintuitive, but it has to do with your autonomic nervous system.
Your autonomic nervous system is the system that is responsible for all of the processes in your body you don’t have control over (heart rate, blood pressure, digestion, etc.). It is made up of the sympathetic nervous system and the parasympathetic nervous system, often referred to as the “fight or flight” and “rest and digest” systems.
These two systems work in conjunction with each other to make sure that you are responding appropriately to different situations. Your body is constantly responding to physical and psychological stressors and the relative contributions of the sympathetic and parasympathetic systems depend on the time of day, physical exertion, psychological stressors, and changes in the environment.
There is a dynamic relationship between these two systems to make sure that you are constantly adapting, responding, and adjusting to maintain homeostasis. Therefore a high HRV is indicative that you are able to recover from stressors properly, and is a marker of good self-regulation, resilience, and adaptability.
On the other hand, low HRV is indicative of stress as there is a lower activation of your parasympathetic system. If you have a low HRV, you are unable to recover properly from stress or changes in your environment. Low HRV has been shown to be predictive of a number of acute and chronic health issues including depression, anxiety, stress, inflammation, diabetes, and chronic pain.
That being said, if you decide to measure your stress levels via HRV, don’t worry so much about the number you get. While a high HRV is associated with good health, HRV is very individual! It’s much more useful to pay attention to how your HRV changes from day to day. And once you start paying attention to it, you might start to see patterns between the days you have a high HRV and the days you have a lower HRV.
If you’re measuring your HRV, here are a few important things to note:
1. Fitness trackers and devices are usually only measuring your heart rate for a minute or so. This is just a small sample of the day, so you should try and measure it a few times per day for the most accurate readings.
2. Try and make one of those measurements first thing in the morning, as it will be a good indication of how rested and recovered you are for the upcoming day.
3. As HRV is a measure of both physiological and psychological stress, you should make sure that you are relaxed when you take your measurement. Sit in a comfortable position and be completely still during the entire measurement. Also don’t measure it within a couple hours of working out!
Hopefully you have a better understanding of what HRV means and the science behind it. Of course, this isn’t the only indicator of health, however it’s one that doesn’t take long so you can do a spot check really quickly and determine how you want to proceed for the rest of the day.
Unfortunately, in today’s fast-paced world we are often in a state of fight or flight. So if you get a “high” stress score, there’s no reason to panic, but start to pay attention to your values and trends. If you’re often getting high or extreme stress scores, it might be an indication that you’re in a state of chronic stress, are run down from work, or maybe you’re just tired from a really hard workout the day before. Listen to your body and on those days, try to prioritize your sleep, and take some time to unwind and de-stress.
What are we finding in the research?
We know that sleep is important for recovery and regeneration, and it is well established that HRV is higher during sleep, particularly non-rapid eye movement sleep (NREM). This is why if you’re feeling stressed or burnt out, a simple solution is to just get a good night sleep!
Recently, a group of researchers wanted to see if naps had the same effect on HRV. The researchers studied a group of 25 healthy men and measured their HRV during a daytime nap. They found that HRV increased during NREM sleep, particularly during deep sleep.
The researchers suggest that, similar to a good night’s sleep, a daytime nap has beneficial effects on cardiovascular health and can help to decrease stress.
This is just another reason to fit in a daytime nap when you have the chance!
