What is HRV?
HRV (heart rate variability) is simply a measure of the variation in time between each heartbeat. This variation is controlled by a primitive part of the nervous system called the autonomic nervous system (ANS). It works behind the scenes, automatically regulating heart rate, blood pressure, breathing and digestion among other important tasks. The ANS is divided into two main groups: the sympathetic and the parasympathetic nervous system, also known as the "fight or flight" response and the relaxation response.
HRV may offer a non-invasive way to signal imbalances in the autonomic nervous system. Based on data collected from many people, if the system is in more of a ``fight or flight'' response (stress), the variability between successive heartbeats tends to be lower. If the system is in a more relaxed state, the variability between beats may be higher. HRV is a good indicator of the state of health seen in an overall perspective