Measuring Stress Via Heart Rate

In last week’s post we learned how the heart reflects your body’s overall stress load. By looking at our resting heart rate and the variability in our heart beats we can determine whether we are currently stressed or not. If our stress load is low and our parasympathetic nervous system is dominant then we should see a lower resting heart rate and more variability in our heart beats.

This brings me to a very important point when we discuss how to use our heart to measure our stress load.

The context in which we take the measurement is important.

Our body can increase its stress pretty much instantaneously. This is a good thing, especially in times of immediate danger. If we need to get to safety quickly, being able to “flip the stress switch” can be life saving. Our body immediately starts mobilizing fuel to our muscles, our heart rate goes up, heart rate variability goes down, blood starts moving around the body faster, our breathing rate increases, our senses become more heightened.

If you were to measure your heart rate and heart rate variability (HRV) during this time it would look pretty bad, and rightfully so, you are in danger (or at least your brain thinks you are).

So when is the optimal time to measure your stress load? Obviously the situation in which we decide to take the measurement is going to affect the outcome.

For nearly everyone there are two times over the course of 24 hours where stress should be at its lowest.

  1. While you are sleeping.
  2. When you first wake up in the morning

If we measure our heart rate and HRV during these times and our heart rate is high and our HRV is low then it’s probably a sign you are overly stressed.

The ability to measure your heart rate is pretty common these days. Any device you put on your body seems to have the ability to measure your heart rate. However when it comes to measuring heart rate to assess our stress level we need to be able to do it accurately and do it consistently.

I have been using devices that measure heart rate for many years now, and I find anything that measures your heart rate on your wrist can be prone to inconsistencies. I can’t tell you the number of times I am exercising and look down at my watch only to see my heart rate barely above what I would normally see sitting down!

I am not saying the wrist based heart rate monitors are useless, they aren’t…however the way they measure heart rate is just prone to inconsistencies which can make measuring heart rate and heart rate variability a little frustrating.

This is important in deciding when and how to measure your resting heart rate and measure heart rate variability.

If we want the most consistent and reliable heart rate measurements then using a chest strap heart rate monitor and an app and doing the measurement first thing in the morning is going to give you the best results.

There are other devices on the market now that are measuring heart rate from the finger. The Oura Ring is probably the most popular but there are more and more coming to the market as time goes on. The finger is actually a very good place to measure heart rate due to the vascularity of the finger. You may have gone to a medical professional and they stick a device on your finger to measure your heart rate, this is exactly why they use that device. A ring is also less prone to abnormalities in the reading from light and movement than something worn on a wrist.

This makes devices like the Oura ring a pretty good choice for measuring resting heart rate and HRV. Devices like the Oura ring tend to calculate HRV over the course of a night. The benefit of this is that it’s done automatically for you, no need to do what I outline below. The main downside of these devices tends to be the price. While not overly pricey, they are still more expensive than the option I talk about next.

A chest strap heart rate monitor measures your heart rate the same way an EKG would in a hospital, so it’s very consistent and accurate. The best chest strap heart rate monitor out there is the Polar H10. It’s relatively inexpensive given how good it is. In addition it is compatible with any bluetooth device, meaning you can pair it to all kinds of fitness equipment to track heart rate, so it has uses beyond just measuring your resting heart rate and HRV. That said any chest based heart rate monitor is going to be good enough, so if you already have one don’t feel like you need to go buy a Polar H10.

As far as what app to use, the choices are endless.

Personally I like iThlete. It is simple, straightforward, and allows you to not only measure your resting heart rate, and HRV but also enter subjective data about sleep, diet, stress, mood, and fatigue…all of which are important when assessing your measurement.

Other popular apps are EliteHRV and HRV4Training. Ultimately you just need to find one that you like and stick with it.

If you are using iThlete here are the simple steps to taking your measurement

  1. Wake up
  2. Use the bathroom if you need to
  3. Put your heart rate monitor on
    1. I find using electrode gel helps a lot with mitigating any kind of connectivity issues. You can pick up two bottles for pretty cheap on Amazon.
  4. In a seated position, open the app and begin the test. Follow the breathing cues in the app. It should only take a minute to complete.
  5. Fill out the subjective questions
  6. You are done!

The steps for other apps will be similar.

After you begin measuring your heart rate and HRV you need to do it consistently for a few weeks in order to establish your own baseline. There are going to be fluctuations in both your heart rate and HRV from day to day so if you just take sporadic measurements every so often it will be impossible to establish a solid trend.

Think of tracking your resting heart rate and HRV like you would tracking your weight. Your weight goes up and down everyday. If you look at your weight day to day it would be impossible to tell whether you are losing weight, gaining weight, or maintaining weight and if you weigh yourself sporadically you have no idea if it was a high day, low day or an average day. However if you weigh yourself everyday and then zoom out and look at your weight over the course of weeks and months a clear trend will emerge.

This is also true for your heart rate and HRV, you need to look at the trend to determine if you are becoming less stressed, more stressed, or maintaining a balance of stress and rest. Therefore I rarely act on a single heart rate or HRV measurement in insolation. I would need to see a trend in one direction or another for at least a week before taking action.

Below is a resting heart rate and HRV trend that I would consider positive. The red dotted line is the heart rate and the blue line with the green dots is the HRV measurement. The solid blue line without the green dots is the HRV trend line. As you can see the HRV measurement is higher than the heart rate measurement, this is a good sign, it means the client is not overly stressed.

The below example is a trend where I would start to be somewhat concerned about. You can see their heart rate, the dotted red line, is starting to rise and their HRV, the blue dotted red line, is starting to decline and their heart rate is above their HRV. In addition you start to see HRV measurements that have yellow and red dots, indicating the app thinks they are overly stressed.

When I see something like this in a client I begin to ask questions about how they are feeling. If their subjective stress rating is high and their HRV is declining I will start to take action to eliminate whatever stress we can and also introduce more stress relieving activities.

What types of things would I recommend to the client above?

In the next blog post in their series we will discuss what types of things we would do in the case of a declining HRV to help turn things around. To be the first to know when that blog post is released sign up for my newsletter using the form below. Each week you will get actionable information that you can use to overcome your greatest obstacle and reach whatever goal you are trying to achieve.

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