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 ...

Heart rate variability (HRV) is the variation in the time between two consecutive heartbeats over a specific period. Doctors may use HRV as an indicator for certain aspects of a person’s health, ...

Thanks to the proliferation of smartwatches and fitness trackers, it’s never been easier to log your heart rate while running: Simply don the device (watch, monitor, or other wearable), start your ...