HRV Explained

Heart rate variability shows up in almost every training app now, usually as a single morning number with a green, yellow, or red label attached. The number is useful. The label oversimplifies it.

What HRV actually measures

HRV is the variation in time between consecutive heartbeats, and it reflects the balance between your sympathetic ("go") and parasympathetic ("rest and digest") nervous systems. Generally, higher HRV suggests your body is leaning toward recovery and readiness; lower HRV suggests it's under more stress — from training, but also from poor sleep, illness, travel, or life stress unrelated to sport at all.

Why measurement conditions matter

HRV is sensitive to almost everything, which is exactly why consistency in how you measure it matters more than the raw number on any single day. Measured first thing in the morning, in the same position, before caffeine, it becomes genuinely useful as a trend. Measured inconsistently, it becomes noise dressed up as data.

What a dip means — and doesn't

A single low reading after a hard session is expected and not a warning sign; that's the point of training stress. A trend of readings sitting below your normal range for several days in a row is the more meaningful signal, and it's still a prompt to look closer, not an automatic verdict that something is wrong. HRV can dip from a great hard training block just as easily as from under-recovery — context decides which one it is.

Reading it alongside how you feel

The most reliable use of HRV isn't as a standalone traffic light — it's as one input alongside subjective readiness: how you slept, how yesterday's session felt, what's happening outside of training. When both agree, the picture is clear. When they disagree, that disagreement itself is useful information, and usually means it's worth erring toward caution rather than trusting the number over how you actually feel, or vice versa.