Heart rate variability (often referred to as HRV) is the measure of the variation in time between each heartbeat. These variations are so small that unless you’re hooked up to a specialized device you won’t be able to detect them for yourself, but they’re nonetheless incredibly important to your overall health and wellbeing. 

HRV is a metric that is recorded by many of the best fitness trackers (opens in new tab), including the Apple Watch, Garmin Fenix 7 Sapphire Solar (opens in new tab) and several Fitbit bands. It shows you how well your body is able to respond to signals from the parasympathetic and sympathetic nervous systems (the latter controlling the body’s fight-flight response and the former acting as brake) and adapt to the change in environment.

Source link