What HRV actually measures
Your heart does not beat like a metronome. Even at rest, the gap between one beat and the next shifts by milliseconds, widening when you exhale, narrowing when you inhale. Heart rate variability is the measure of that fluctuation. A higher variability generally means your autonomic nervous system is balanced and adaptable. A lower one signals that your body is under strain, whether from hard training, poor sleep, or chronic stress.
