HRV
Heart-rate variability, read every morning before coffee ruins the number.
The number
Heart-rate variability is the gap between beats, and it's the closest thing your body has to an honesty meter. High HRV means you're recovered; low means you're not — yet.
How we read it
metric rMSSD, 5-min waking window window first 2 minutes after wake baseline your rolling 30-day range verdict recovered / strained
Why it matters
HRV is the first thing that drops before you get sick, overtrain, or blow a night of sleep. Read it daily and you stop being surprised by your own body.