Heart rate variability (HRV)

Heart rate variability (HRV) is the tiny variation in time between heartbeats: higher than your usual generally means you are well recovered, lower means stress or fatigue.

• It is very individual: compare yourself only with your own baseline, never with others.
• Read the trend over 7 days rather than one morning; a single low value means little.
• Several days below your normal range, with a higher resting heart rate, call for easier sessions.
• Alcohol, poor sleep, illness, late meals and stress lower it as much as training.

Apple Watch measures it during the night and saves it in Apple Health, where you can follow its trend.