Reaction time is the least interesting part of a start

Broadcasters put the reaction figure on screen because it is easy to measure, not because it separates the athletes who get away well.

The number that appears next to a sprinter's name a second after the gun is the gap between the report and the moment force on the blocks crosses a threshold. It occupies about a tenth of a second, and the spread between the quickest and slowest in a good final is a few hundredths. Meanwhile the first two steps take about half a second and produce a spread several times larger. We put the small number on screen because a pressure plate can measure it cheaply.

What actually decides the start is what the athlete does with the force once the reaction has happened. Two things matter. The direction of the push, which needs to be far more horizontal than intuition suggests, and the time spent applying it, which in the first stride is enormously longer than in any stride later in the race. A good starter is not quick off the blocks in the sense of leaving early. He is slow off the blocks in the sense of staying in contact and pushing for longer, at an angle that sends him down the track instead of up into it.

This is why the athlete who looks explosive in the first ten metres is often not the one in front at thirty. Popping up early feels fast and produces a lot of vertical force, which does nothing except make the next contact happen sooner and shorter. The correct shape looks almost laboured from the side. Shin angle low, hips travelling forward, head down for longer than a nervous coach is comfortable with.

There is a legitimate counterargument in the shorter indoor events, where the race is so brief that a hundredth on the reaction is a real fraction of the margin. Fine. Even there, I would spend the coaching hour on the drive phase rather than on twitching at a gun, because reaction time is largely inherited and barely trainable, while the first three contacts are trainable for years.

What irritates me is that the on-screen figure gets treated as a verdict on an athlete's sharpness. A sprinter with a slow reaction and a beautiful drive will beat a twitchy one with a bad angle every time.

The gun is not the race. It is only the loudest part.