The claim that a start reaction can be trained needs a tighter definition

What the measured interval contains

The interval recorded between a signal and a detected movement includes sensory processing, motor planning, muscular activation and the time taken to generate measurable force. Those components have different physiological bases and there is no reason to expect them to respond to training in the same way. Treating the total as a single trainable quantity therefore combines processes that a coach can influence with processes that are close to fixed.

Improvement in the total can come entirely from the force-production component while the perceptual component is unchanged. Any claim that reaction has been improved should specify which component moved, and almost none of them do.

Anticipation is not reaction

An athlete who has learned the rhythm of a starter cadence is predicting the signal rather than responding to it after arrival. Prediction produces faster apparent responses and is a different skill with a different failure mode, since a mistimed prediction is costly. Rules that disqualify movement before a threshold exist precisely because the boundary between anticipation and response is difficult to police.

A training programme that improves the measured interval by improving anticipation is doing something real and something other than what it claims. The distinction matters because anticipation transfers poorly when the cadence changes, while genuine perceptual improvement would not.

Position in the blocks does most of the work

The force an athlete can apply immediately depends on joint angles, block settings and how much tension is held at the moment of the signal. Small changes in those settings alter the time required to reach the force threshold that a detection system registers. That is a mechanical adjustment rather than a change in responsiveness, and it is highly trainable and highly individual.

Because it moves the same number that reaction training claims to move, credit is routinely assigned to the wrong process. Separating them would require measuring the perceptual latency independently, which is possible in a laboratory and not at a track meeting.

The limits of what practice can shift

The purely perceptual and neural components of a simple response are constrained by conduction speeds that are not obviously modifiable by practice. That does not mean nothing improves, since attention state, arousal and familiarity with the protocol all influence performance on the day. It does mean the headroom in that component is smaller than the marketing around start training generally implies.

Most of the available improvement therefore sits in mechanics and in preparation rather than in the athlete becoming faster to perceive. This is a case where the mechanism, once stated carefully, tells you where to look rather than leaving the question open.

Why the loose claim persists

Reaction is an appealing thing to sell because it sounds innate and therefore feels valuable to improve. The measurement is also published at competitions, which supplies a visible number to point at without any breakdown of its components. A visible aggregate number attached to a vague claim is an ideal environment for confident assertions that cannot be checked.

Coaches working seriously on starts tend to talk about angles, tension and the first three steps rather than about reaction as such. The vocabulary gap between the practitioners and the marketing is the clearest signal available about which claim is doing the work. Where two groups describe the same activity in different terms, the group that has to produce results is usually the more accurate one.