Our heart is a wonderful organ. It can contract on its own without any outside input. However, without control from the central nervous system, we cannot adapt to changes in our body and our daily activities.

Is it possible to estimate one’s stress level by heart rate? Turns out – yes! Your heart rate tells more about you than you think.

Autonomic control

An autonomic (or vegetative) nervous system that is in charge of our heart consists of two components: sympathetic and parasympathetic nervous systems. The sympathetic nervous system is responsible for our fight-or-flight response. It’s activity prepares our body (including our heart) to the challenges we face during the day. As opposed to sympathetic nervous system, parasympathetic is our recovery system. It is responsible for rest and feeding.

There should always be a balance between the two. To make it more clear for you, consider the following analogy.  Sympathetic and parasympathetic nervous systems are like gas and breaks of a car. In order for it to move without damaging the engine they must work together. Our heart is the engine.

Stress level and HRV

In order to maintain our daily activities, the heart always receives stimulation from both of the systems. They concurrently work together adjusting the heart rate to meet the demands of our body even when we are sleeping, which leads to subtle irregularities of our heart rhythm.

By analyzing beat-to-beat variability (also known as HRV), we can easily estimate the ratio of activities of sympathetic and parasympathetic nervous systems. This allows us to estimate one’s stress level.

Our body reacts to stress by increasing sympathetic tone. When we are stressed, our heart rhythm tends to be more stable resulting in a low variability. In contrast, a relaxed state is usually associated with a high HRV.

We estimate stress level using standard algorithm developed by a soviet physiologist R.M.Bayevsky. Normal range for stress index is 40 – 150. Values above 150 is considered to be associated with stressed condition. Values below 40 are often associated with sleep (it is like that for example if you stay awake too long).

Even though there are standards for HRV, all estimated parameters and normal ranges can vary depending on your individual features and lifestyle. Only a trained physician can correctly interpret the recording, with respect to your individual features and medical history.

Don’t stress out!