Heart rate variability has established itself in medicine since the 1960s as a valuable tool for assessing stress, recovery and the body's adaptability.

It describes the fluctuations in the time intervals between heartbeats and shows how adaptable the heart is to internal and external stimuli.

The autonomic nervous system controls this adaptation via the activating sympathetic nervous system and the calming parasympathetic nervous system, particularly via the vagus nerve.

A high HRV is considered a sign of a balanced and flexible nervous system, while a low HRV often indicates stress, exhaustion, or impaired regulation.

Mechanisms such as breathing and blood pressure control continuously cause small changes in heart rate, which make HRV measurable.

This allows HRV to be used as a simple, non-invasive tool to assess the condition and balance of the nervous system.