Can you measure stress?

Can stress be measured? Stress is a pronounced problem in many workplaces. High stress causes low commitment, high staff turnover, reduced productivity and high costs for short- and long-term absences. Most workplaces have a range of different activities to reduce stress, but have difficulty seeing the effect of it. That leads us to the important question Can stress be measured? And if so How?

The short answer is: YES!

With questionnaires and employee surveys? No. If answered truthfully, they can provide signals of perceived stress, but the majority of us do not actually feel the body’s true stress load.

With blood tests? No. When stress-related illness has gone so far that it shows up in the blood as hormone disturbances, blood tests are part of the medical examination, but as an employer you want to intervene long before that.

With statistics for sickness absence? Well. Both short- and long-term absences correlate with stress, but as an employer you can rarely afford to wait so long for a measurement result.

With continuous HRV measurement? Yes! HRV is the primary biomarker of stress. Then you see both the body’s stress level and in real time exactly when the body is winding up and winding down. This is how Linkura helps employees and employers measure and increase their resistance to stress.

Below follows an in-depth look at the best way to measure stress – with HRV

We let our very own doctor in physiological measurement technology, Anders Tjernvik, offer the long answer.

What is stress?

Stress is a physiological (bodily) reaction to an actual or perceived threat in our environment. A system developed by evolution over a long period of time to strengthen our chances of survival in emergency situations. This is what is usually called the flight response or fight-or-flight. Simply a way for the body to physically prepare itself for fight or flight.

The biologically relevant parts are first and foremost the central nervous system which can be compared to a car where stress activates the “gas” in the form of the sympathetic nervous system and recovery causes the body to “brake” through the parasympathetic nervous system. Stress also secretes a lot of hormones, the two most important stress hormones being cortisol and adrenaline.

The stress reaction starts in the brain and means that the “gas” is activated through the sympathetic nervous system and that stress hormones are sent out into the blood. The purpose is basically that we should become present, sharpened and therefore better at taking on the danger. In the short term, stress is therefore something positive.

Something that not many people are aware of is that physiologically, i.e. in the body, there is no difference between mental and physical stress. Both parts stimulate the stress system and burden the body in roughly the same way!

Is stress dangerous?

Stress in itself is not the least bit dangerous. On the contrary, it is an excellent driving force that makes us perform extra when we need it. Unfortunately, our stress system has not developed at the same rate as our civilization and our way of life. In our modern complex society, both at work and at home, it is therefore triggered by everything imaginable that we deal with and worry about, and the body “needs” to be in a stressed state often and for a long time. When the stress response is on for long periods of time, the body and brain take damage. Cortisol is the bigger culprit in the drama because the hormone is often present for long periods of time. Cortisol causes fat and sugar to enter the bloodstream, which is not good for us. The research suggests that it is directly harmful to structures in the brain. The key is therefore to balance the stress with physiological recovery as often as possible. This simply means creating periods without stress hormones in the blood and with the “brake” on in the nervous system.

How do I know if the body is stressed?

To measure stress, you need something that either captures the amount of stress hormone in the blood or in which state the nervous system is. It is best to measure the nervous system, which is connected to both the heart and the brain. This is done with heart rate variability (HRV), measured by ECG.

To directly measure hormone levels, blood samples are the most stable, but you can also estimate the levels via saliva. These are methods used, among other things, in healthcare to investigate medical conditions that lead to hormonal disorders. However, they are not useful for everyday use because each measurement only gives a snapshot, and also requires sampling and lab analysis. When you want to measure and understand your stress in everyday life, sampling is not an optimal solution. Then two other methods are available instead, skin conductance measurement or heart rate variability.

When the nervous system gas is on, the sweat glands in the skin are triggered. Sweat conducts electricity, so by measuring the conductivity of the skin, you can measure the stress level. Such a measurement is included, for example, in a lie detector test because lying triggers the same activation as a stress reaction. Unfortunately, this method is not very stable because sweating is also affected by the temperature of the environment.

Then it is more interesting to look at the most central organ in the stress reaction, the heart, together with the brain. The heart is strongly affected by the nervous system and stress hormones. When you are recovering, you can clearly see how the heart speeds up when you breathe in and slows down when you breathe out. This is how the heart works in a calm body. Under stress, however, this variation disappears as the heart is stimulated to beat a little faster and more regularly. When we are instead in recovery, the heart beats more slowly and the stroke length varies greatly from beat to beat. How much the heart rate varies is thus an excellent measure of your current stress level and is called heart rate variability or HRV for short. High variability indicates a body in recovery while low variability indicates a body under stress.

And heart rate variability is measurable?

Yes absolutely! An easy way to test this on yourself is to feel or listen to how the pulse varies from beat to beat. However, it does not provide precise information, the most stable way to measure HRV is instead with the help of ECG equipment. ECG is an abbreviation of electrocardiography and is based on listening for the electrical signals that are formed in the tissue of the heart when it beats. The signal provides an enormous amount of information and is often used in healthcare to diagnose or monitor the heart. One of all the parameters that can be calculated from an ECG is precisely HRV and thanks to the signal’s richness of detail, it can be done with very high precision.

You can also measure HRV with optical technology, for example on the wrist, so-called photoplethysmography (PPG). That method is based on measuring variations in how much blood flows through the skin, which correlates with the frequency with which the heart beats. The disadvantage of this technique is that you need to sit basically completely still because the slightest movement disturbs the weak variations in the wrist’s blood flow. Therefore, watches, rings and bracelets do not work very well to measure stress in everyday life.

But if stress starts in the brain, can’t you measure it there?

Yes, that is the million dollar question, if you can measure directly on the brain to capture the stress reaction in its very earliest stage. Research is underway where the collected electrical signal from the brain is picked up from the skin surface of the head, or infrared light is shone down through the skull bone to measure the blood flow in different parts of the brain. The signals are complex and still very difficult to interpret. However, there are indications that the electrical activity of the brain changes in connection with the escape response.

If we allow ourselves to speculate, it is not an advanced guess that in the relatively near future we will see implantable chips that measure ECGs from the heart to help us control stress and prevent disease. If the rapid development in signal processing and machine learning continues, it is not inconceivable that we will also see similar solutions with signals from the brain.

How do we measure stress?

Linkura’s research comes from the comparison between PPG (measuring through the skin with a watch or ring) and ECG (measuring directly over the heart) Basically all other players who measure HRV have chosen to use PPG because that technology is very available. A decent camera in a smartphone or an optical sensor in a smartwatch is enough. However, extensive research clearly shows that PPG sensors provide far too little information about stress. Not so strange since the measurement takes place far from the heart. Also, they have too much of a problem with motion artifacts (interference caused by motion) to be useful. It is simply not possible to see your stress in real time with watches and rings. We therefore decided early on to invest in ECG as this is the technology that provides the best precision and benefit in relation to ease of use.

One challenge we faced, however, was that there was no solution on the market for measuring continuous ECG in everyday life. In healthcare, portability is not an important factor and the ECG equipment that existed consisted of stationary boxes with lots of sticky electrodes and leads.

We therefore started the development of our own portable ECG meter, which was designed from the ground up to be as user-friendly as possible without sacrificing signal quality. After some challenging engineering internally, we have had our patented ECG meter out with users all over the world for a few years now. What is completely unique is that you can listen to your heart with medical signal quality while the meter is small and can be worn in a regular heart rate strap around the chest.

As we mentioned earlier, the body’s reaction to physical and mental stress is basically the same, but thanks to a patented algorithm we can actually distinguish between them. In Linkura’s app, the user can upload and view their data and immediately get insights and analyzes about their stress and recovery.