What your heart-rate variability is trying to tell you

Heart-rate variability is the variation in time between consecutive heartbeats, and it is a remarkably good proxy for how much capacity your autonomic nervous system has left. High variability means a system that can adapt. Low variability means one that is bracing.

The most common mistake is comparing your number to someone else's. HRV is highly individual — driven by age, genetics, and fitness — and a value that is excellent for one person is unremarkable for another. Your baseline is the only benchmark that means anything.

What is worth watching is the trend, and the outliers against your own norm. A sharp drop typically precedes the subjective feeling of being run down by a day or two — which makes it one of the few signals that lets you act before you crash rather than after.

Used well, it becomes a simple daily decision rule: suppressed HRV is a day to train lightly, prioritise sleep, and consider a sauna or HBOT session rather than a hard block of intervals.