Your heart is racing….
Did you just finish sprinting?
Are you about to give a big presentation at work?
Did you just get in an argument with your spouse?
Are you watching a scary movie?
Did you just get into a cold plunge?
Did you just eat something you might have a sensitivity to?
What do all these situations have in common?
Some are “good” stressors, some may be “bad” stressors, but they are all stressors and they all tend to raise your heart rate.
You spend some time in a sauna.
You take a nap.
You watch the sunrise or sunset.
You get a massage.
You take a walk.
You do some breath work.
These activities tend to slow the heart rate in most people and are considered relaxing and stress relieving.
The heart can be a great reflection of our current stress load.
Why does this happen? What in our body is telling our heart to change how fast it is beating in response to stress?
It will come as no surprise that the brain is controlling our heart rate. The brain is interpreting what is happening both inside and outside of our bodies and relaying that information to the nervous system, more specifically the autonomic nervous system.
As you might be able to infer by its name, the autonomic nervous system controls functions within your body without you having to think about it. Things like making your heart, your breath, and your digestion are all influenced by the autonomic nervous system.
There are two parts of the autonomic nervous system, the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system is the “flight or fight” part of the autonomic nervous system while the parasympathetic is the “rest and digest” part of the autonomic nervous system.
As you can tell by these nicknames the sympathetic nervous system prepares your body to handle stressful situations while the parasympathetic system promotes more relaxation and recovery when stress is low.
The sympathetic nervous system is connected to the heart via the sympathetic cardiac nerves and the parasympathetic nervous system is connected to the heart via the vagus nerve.
With the basic physiology out of the way, the next question is how can we determine how much stress we are under using this knowledge?
Before going any further there is one other piece of information that will be useful in this discussion.
If we could remove the influence of the autonomic nervous system on the heart it would on its own beat around 100 beats per minute due to its own internal pacemaker called the sinoatrial node. However we know the heart can beat slower and faster than this, it’s the autonomic nervous system which causes this to happen.
The parasympathetic nervous system is what’s responsible for a resting heart of less than 100 beats per minute. However the sinoatrial node is always trying to work against the parasympathetic system and get the heart back to 100 beats per minute. Due to this constant battle between the sinoatrial node and the parasympathetic nervous system the rate at which our heart beats is not constant.
This is easier to understand via a simple example.
Say your heart rate is 60 beats per minute. You might assume that means that your heart beats once per second, but in reality all that tells you that over the course of 1 minute you had 60 heart beats, it does not say how those heart beats were distributed across the 60 seconds.
When you are not overly stressed there tends to be a slight difference in the time between heart beats. When the parasympathetic nervous system is depressed not only will your heart rate generally be higher because it won’t be slowing it down, but the variability between the heart beats will be more consistent.
Given this knowledge we can therefore conclude that greater variability in your heart rate would mean there is more parasympathetic activity and therefore you are in more of a “rest and digest” state. If your parasympathetic activity is decreased then you are in more of a “flight or fight” state and there will be less variability in heart rate.
- The autonomic nervous system receives signals from the brain about stress
- The autonomic nervous system influences your heart rate to either speed up or slow down based on the amount of stress you are under
- The autonomic nervous system has two branches, the sympathetic (fight or flight) and the parasympathetic (rest and digest)
- When left on its own, without the autonomic nervous system’s involvement, the heart would beat approximately 100 beats per minute
- We know our resting heart rate is much less than 100 beats per minute, indicating the parasympathetic nervous system is slowing it down
- The battle between the heart’s natural rhythmic beating and the parasympathetic nervous system trying to slow things down causes variability in heart beats, this is known as heart rate variability
- The higher the heart rate variability and the lower the heart rate the more influence the parasympathetic nervous system is having and therefore the more relaxed we are.
- The lower the heart rate variability and the higher the heart rate the less influence the parasympathetic nervous system is having and the more stressed we are
Now if we could only track heart rate and heart rate variability, then we could take this information and use it to improve our stress and become more resilient…
Luckily we can!
In the next post we will discuss how to track HRV, how to interpret the data, and how to use the data to help you reach your goals! To be the first to know when the next blog post is published enter your email address below to sign up for my newsletter and I will email you as soon as it’s available.