The relay changeover: twenty metres in which two runners solve one problem

What the exchange is actually optimising

The purpose of a relay exchange is to move the baton forward without either runner slowing down, which is a problem of matched velocity rather than of handling. A baton passed between two runners travelling at different speeds requires one of them to adjust, and any adjustment is a loss of speed somewhere. The ideal exchange happens when the outgoing runner has reached a speed close to that of the incoming runner and the gap between them is stable.

That state exists only briefly, which is why the exchange zone is a specific distance rather than an area within which the pass may occur casually. The consequence is that the pass is a timing problem first and a coordination problem second, which is the reverse of how it appears.

The mark and the decision to go

The outgoing runner places a mark on the track at a distance determined in training, and begins running when the incoming runner crosses it. The mark encodes the incoming runner's speed and the outgoing runner's acceleration, so it is specific to a pair rather than to an athlete. It has to be adjusted for fatigue, since a runner arriving at the end of a hard race is travelling more slowly than the same runner in practice.

A mark that is too long means the outgoing runner escapes and the pass happens beyond the zone or not at all. A mark that is too short means the incoming runner arrives too quickly and has to decelerate, which is the more common and less visible failure.

Why the outgoing runner does not look

A runner who turns his head to locate the baton disrupts his own acceleration, because the shoulders rotate and the arm action is interrupted. The blind exchange therefore trades certainty for speed, and it depends entirely on the mark and on the incoming runner's call. The visual exchange used in longer relays is slower but far more reliable, which is why the choice depends on how much the acceleration matters.

In a short relay the acceleration matters a great deal, since the outgoing runner is trying to reach top speed within a very short distance. The trust involved is not sentimental but structural, since the technique cannot function if the outgoing runner hedges by half-turning.

The hand and the arm

The outgoing runner presents a stable target by extending the arm backwards and holding it still, which is difficult while sprinting. Holding the arm still requires the opposite arm to compensate, so the whole upper body is running an unfamiliar pattern during the exchange. The incoming runner places the baton rather than pushing it, since a push disturbs the outgoing runner's balance at the moment he most needs it.

Whether the exchange is upsweep or downsweep affects how far along the baton each runner grips, which matters over multiple exchanges. The baton has to end up in a position from which the next exchange is possible, so each pass is constrained by the one after it.

Where the time is actually lost

A dropped baton is catastrophic and rare, while the routine loss is a fraction of a second surrendered to deceleration that nobody notices. An incoming runner who has to reach forward or slow slightly loses speed at the very end of his leg, where he has the least capacity to recover it. An outgoing runner who starts late spends the first part of his leg accelerating from a lower speed than the exchange should have provided.

These losses accumulate across three exchanges, which is why teams of individually slower runners regularly beat faster ones. The exchange is therefore the part of the event with the most available improvement and the least attention paid to it.