Heart-rate variability

Heart-rate variability is the natural variation in time between heartbeats. It reflects how the nervous system regulates the heart and changes with breathing rhythm, posture, activity and stress. Higher resting variability is generally associated with good adaptability, while lower values can accompany stress, poor sleep, illness or ageing.

Slow breathing at around five to six breaths per minute reliably increases short-term variability during the practice itself. Readings from wearables are useful for personal trends but vary between devices and should not be over-interpreted.