The morning readiness score is telling your athlete how to feel

A wearable produces a number before breakfast, and by lunchtime it has changed the session more than the coach did.

An athlete wakes up, checks a strap, and gets a two digit score. Green, amber, red. Before anyone has spoken to her, before she has walked to the track, she has been told what kind of day this is going to be. I think that is a worse arrangement than the one it replaced.

Start with what the number is. Most readiness scores are built largely on heart rate variability measured overnight or on waking, blended with resting heart rate and sleep estimates. Heart rate variability is a real signal. It is also enormously sensitive to things that have nothing to do with training, including a late meal, a warm room, alcohol, a stressful phone call, the phase of a menstrual cycle, and the simple question of whether the strap sat properly. Day to day variation in a healthy athlete is large enough that a single morning reading tells you close to nothing on its own.

The useful version is a rolling trend across a week or more compared against that individual's own baseline. That version is genuinely informative and can flag an athlete heading towards trouble a few days before she feels it. The version on the phone screen is a single day, dressed up with a colour.

Here is the part that bothers me most. The score is not passive. Show an athlete a red morning and she will train like someone who has been told she is tired. Show her green after a poor night and she will push through something she would otherwise have flagged. The measurement changes the thing it is measuring, which is a problem physics gave up arguing about a century ago and sport is still pretending does not apply.

My preference is blunt. Athletes should not see the daily number. Staff should see the trend, athletes should report how they feel in their own words first, and the two should be compared. When they disagree, that disagreement is the interesting data.

A coach who has watched someone warm up for four years is a decent instrument. He was not made obsolete by a wrist strap.