Heart rate variability (HRV)

The Heart Rate Variability (HRV) is the difference in time between the heartbeats. This time is constantly varying unless you have a pacemaker. On the basis of the variability of the time between the heartbeats, the degree of activation of the autonomic nervous system is measured. The autonomic nervous system is the part of the peripheral nervous system that regulates a large number of functions (unconsciously) such as breathing, digestion, heartbeat, etc. It can be divided into the sympathetic and parasympathetic nervous system.

With stress, the sympathetic nervous system is activated, the body prepares to 'fight or fly'. Breathing and heartbeat accelerate, the pupils dilate, etc.This system is evolutionarily very old and vital. It protects us from danger; just think about how you would react when you are chased by a hungry bear. The chance that you encounter a bear is rather small today, but our body does not distinguish between seeing a bear or being overloaded with work, noise, or feeling pain. When the danger is over one can relax again and the breathing and the heartbeat will become calmer, the digestion will start, etc. When the 'stress network' in our brains is over-stimulated, the sympathetic nervous system will remain active, making it difficult or even impossible to relax.

An HRV measurement gives us an idea about the relationship between the sympathetic and parasympathetic activity at rest.