HRV and Your Sleep

Heart rate variability (HRV) has become a hot topic for those interested in monitoring their own or their clients' sleep, recovery, performance, or overall health.

It’s not a metric that we focused on in medical school, and it’s not one that doctors are frequently reporting on or observing.

But I think we should.

Especially as it relates to sleep.

A lot of what I’ll discuss today is going to be scientific in nature, but it’s just so you understand the importance of HRV and how it relates to sleep.

HRV is one of those pieces of data that should you focus on and watch improve, things will just be a lot better for you (because as you’ll see, HRV kind of tells you how healthy you are).

What is HRV, Really?

HRV is the physiological phenomenon of the variation in the time interval between consecutive heartbeats in milliseconds.

A normal, healthy heart does not beat evenly like we think it does.

Instead, there is constant variation in the milliseconds between heartbeats. In general, we are not acutely aware of this variation, which is not the same as the heart rate (beats per minute) increasing and decreasing as we go about our daily business.

HRV is the measurement in between beats in milliseconds.

Now I could write a lot more about the measurements, but I don’t want to bore you, I want you just to know why it’s so important.

As far as HRV and its function, it’s regulated by the autonomic nervous system (ANS), and its sympathetic and parasympathetic branches.

The ANS is a part of your body that helps control things that you don't have to think about, like breathing, your heartbeat, and digestion.

It works by sending messages from your brain to different parts of your body, telling them what they need to do.

Think of it like a car that has an automatic transmission - you don't have to change gears because the car does it for you. The Autonomic Nervous System does the same thing for your body.

The body has two systems that control how we feel. One system is called the sympathetic nervous system, which gets us excited and ready to do things like run or jump.

The other is called the parasympathetic nervous system, which helps us calm down and relax.

Imagine you're out hiking with some friends.

As your body moves your heart starts beating fast and you feel like you have a lot of energy. That's because your sympathetic nervous system is working hard to keep up with all the movement.

Now imagine once you’re done and you get back home.

You’ll notice you’re starting to feel calm, even sleepy as you settle back into your normal routine. That's because your parasympathetic nervous system is taking over and helping you relax.

So basically, the sympathetic nervous system is like the gas pedal in a car and the parasympathetic nervous system is like the brake pedal. They both help your body do different things depending on what you need.

When your body is relaxed, your parasympathetic nervous system is active, which leads to higher HRV.

When you are stressed or anxious, your sympathetic nervous system is active, which leads to lower HRV.

So, HRV can help us understand how our body is responding to different situations, including whether we are relaxed or stressed.

This is why if you have a wearable and can track HRV you can tell a lot about your sleep.

Remember, this is just a simple explanation and the sympathetic and parasympathetic nervous systems are much more complicated than this.

The sympathetic branch of the ANS is the stress or fight or flight system, getting us ready to act, react, and perform – to meet the different demands that life throws at us.

Sleep is controlled by the parasympathetic nervous system and if your HRV scores are low, it’s telling you something about the quality of your sleep.

What HRV Numbers Mean In Regards to Sleep

If you want to get better sleep, you need to focus on improving HRV.

And if you have something like an Oura ring or a Whoop, you’ll soon find out if your sleep is good based primarily on your HRV alone!

An important thing to know is that HRV is influenced acutely by various factors.

These include exercise (and how hard you exercised), hormonal reactions, metabolic processes, cognitive processes, stress, illness, and recovery.

You can improve your individual HRV by improving health, fitness, stress management, and recovery.

Perhaps the best way to lower stress and improve HRV is following various breathing exercises to help induce a parasympathetic response.

There are several different breathing techniques you can try. 

1. Deep breathing: Take a deep breath in through your nose for a count of four, hold it for a count of four, and then exhale slowly through your mouth for a count of six. Repeat for several minutes.
   
   
2. Coherent breathing: Breathe in for a count of five, and then breathe out for a count of five. Continue this pattern for several minutes, aiming for a smooth, regular rhythm.
   
   
3. Breath focus: Close your eyes and focus on your breath. Simply observe the sensation of air moving in and out of your body, without trying to control it. If your mind wanders, gently bring your focus back to your breath.

Incorporating these breathing exercises into your daily routine or before bed can have a pretty significant impact on HRV and sleep.