Heart rate variability, made simple

Heart rate variability is the natural variation, in milliseconds, between one heartbeat and the next ¹. Your nervous system works like an accelerator and a brake: the “rest and digest” side tends to raise HRV, while the “fight or flight” side, active under stress or after hard effort, tends to lower it ^{1, 2}.

That’s why HRV is often higher when you’re rested and relaxed, and lower after poor sleep, alcohol, illness or intense training ³. Because it varies so much between people and with age, comparing it with your own usual range tells you far more than comparing yourself with others ¹.