Years of training, a lifetime perhaps of dreaming, will have been aimed at perfecting a few moments of effort, the reaction to the sound of a gun, the explosiveness from blocks, the immense power of acceleration and the controlled relaxation towards the finish.
There is no margin for error. A heartbeat's hesitation, the loss even of the time it takes to blink, and the gold medal is gone. Stumble and you are last. As it was explained by the coach Sam Mussabini to the Olympic champion Harold Abrahams: "You think of two things, the pistol and the tape. When you hear one, run like hell till you break the other."
It took Abrahams 10.6sec to do that in 1924 and Carl Lewis just 9.99sec in 1984. Last year, in Rome at the World Championships, Ben Johnson pushed back the horizons of the possible when he needed only 9.83sec to take 46 strides.
In an event where the difference between winning and losing can be as little as a tenth of 1 per cent, all eight in the final on 24 September will have tried something different to give them the edge. Alan Wells, champion in 1980, spent hours punching a speed ball. Valeri Borzov, the Ukrainian who won in 1972, credited hours playing in sand dunes as a child for his explosive legs. Linford Christie, fastest of today's Britons, trained last winter hauling a 25kg weight behind him. Johnson lifts iron twice his body weight.
Analysing what makes the difference has become a science in itself. The University of Ottawa set up a research programme last year for the single purpose of discovering what made Johnson so fast. According to Neil Duncanson, author of the book which accompanied ITV's recent series The Fastest Men On Earth, the scientists discovered the stunning fact that Johnson used 3,000 watts of energy in one stride, enough to light up an average mansion.
Analysis of the films taken of Johnson revealed something more significant. While other sprinters landed each stride on their heel, Johnson ran high on his toes with the ankle fully extended upwards. "Dogs run like that," said Professor Gord Robertson, who led the inquiry.
In Rome the crucial difference between Johnson and Lewis was in their reaction to the gun. The official time-keepers, who can measure the time it takes an athlete's foot to start taking pressure off his block, proved that it accounted for more than half of Johnson's final lead over Lewis.
Indeed, Johnson's reactions are so fast that there have been occasions when they have deceived the electronic starting guns which are set to sound a false start if any athlete reacts more quickly than 0.12sec, reckoned to be the human limit.
In Rome, Johnson's reaction was timed at 0.109sec, inside the limit, but on that occasion the starter let him get away with it. Johnson believes he can be even faster. Lewis says, "Johnson's unbeatable at the start but he's beatable during the race." So which man is likely to become the 21st Olympic 100m champion? Thirteen of the first twenty have been Americans but, more critically, seven of the last twelve have been black.
Dr J.M. Tanner, who measured, photographed and X-rayed 137 athletes at the 1960 Olympics, found the arms and legs of black sprinters were longer, pelvis narrower, calf muscles more slender and the ratio of leg length to body height greater than in white sprinters. So a black athlete has a greater power-to-weight ratio and in events requiring short bursts of muscular power has a natural advantage. It is not by chance that Lewis, Johnson and Christie, asked independently for eight finalists in Seoul, named only one white, the Soviet, Vladimir Krylov.
In the sprints black is best. The question it will take only 10 seconds to resolve around 1.30pm on 24 September in Seoul is which one.
From Olympic Preview 1988 in `The Independent', Thursday 15 September 1988