A readiness score is a mood ring with bluetooth

Heart rate variability measures something real, and the single number your wrist reports each morning is not it.

The strap says sixty one percent recovered. The athlete feels fine. Now what.

Heart rate variability is not nonsense. The beat to beat variation in your heart rhythm genuinely reflects the balance between the two branches of your autonomic nervous system, and a sustained suppression of it in a trained athlete genuinely tends to precede a bad patch. The physiology is sound. The problem is everything that happens between the sensor and the number on the screen.

Start with noise. Day to day HRV in a healthy person swings enormously in response to things that have nothing to do with training. Two glasses of wine. A late meal. A hot room. Waking to an alarm rather than naturally. Position, hydration, the phase of a menstrual cycle, a mild cold you have not noticed yet. Against that background, a single morning reading carries so little information that acting on it is close to acting on a coin.

Rolling averages fix some of that, which is why the better systems compare a seven day mean against a longer baseline. Fine. But now the metric is slow, and a slow metric cannot answer the question people actually ask it, which is whether to do intervals this morning.

Then the composite score. Vendors take HRV, resting heart rate, sleep duration, sometimes temperature and respiratory rate, run them through a weighting nobody outside the company has seen, and print a percentage. That is not a measurement. It is an opinion in a numeric costume, and it is unauditable by design.

Here is my objection in practical terms. I have seen an athlete cancel a session she was perfectly capable of, and would have enjoyed, because a number told her she was compromised. The number created the fatigue. That is not a small harm in a sport where confidence is part of the equipment.

The defensible use is narrow and worth having. Track your own trend over weeks, ignore individual days entirely, and treat a persistent decline alongside heavy legs and bad sleep and low mood as a reason to have a conversation with your coach. That is HRV doing what it can do, which is confirming what your body was already telling you.

And if the strap and your legs disagree on a Tuesday morning, believe your legs. They have been doing this for longer.