Nobody wins the one-lap race, somebody slows down least

Every runner in a four hundred metres is decelerating over the final stretch, so the interesting number is the rate of loss.

The last hundred metres of a one-lap race is a study in controlled collapse. Every athlete in the field is slowing. The winner is the one whose curve falls at the gentlest angle, which is a very different quality from top speed.

This gets missed because the event is filed under sprinting, and sprinting is understood as acceleration. Over one lap the acceleration phase is over almost immediately and the rest is management. An athlete hits close to maximum speed early, holds a float through the back straight in which the effort is high but not maximal, and then spends the last bend spending down whatever is left. The mechanics degrade visibly. Stride length shortens, the arms rise, the shoulders tighten, and the runner who looked most relaxed at two hundred is often the one still moving forward at the line.

Which is why I distrust the habit of projecting one-lap potential from a flat hundred time. Speed is necessary. It is not the constraint. The constraint is how fast the body loses access to it under an accumulating chemical load, and that quality is trainable in a way that raw top speed largely is not.

Training for it is unpleasant in a specific way. It requires running repetitions at speeds close to race pace when you are already in a bad state, so the athlete practises holding form while everything is screaming at them to shorten up. Coaches call this speed endurance and athletes call it worse things.

The tactical version is the split ratio. Go through halfway too fast relative to what you can maintain and the deceleration curve steepens before the home straight, and the last fifty becomes wading. Go too conservatively and the gap you left is not recoverable, because you cannot accelerate late in this event, you can only decay more slowly than the person beside you.

That is the whole race in one sentence. Nobody is coming back at the end. They are just falling apart at different speeds.

If a coach tells you an athlete finished strongly over the last hundred, ask to see the splits. He did not finish strongly. Everyone else finished worse.