Distance races often include athletes who lead for part of the way and then withdraw. Their job is to remove two separate obstacles from the leaders' path.
Air resistance is a real cost
Running through still air still requires pushing air aside, and the energy spent doing so rises steeply as speed increases.
An athlete running directly behind another encounters disturbed air and expends measurably less energy at the same pace.
Over a long race that saving accumulates, and it is largest in exactly the conditions where records are attempted, which is at sustained high speed.
Judging pace is its own burden
Holding an exact speed for a long distance requires constant small adjustments, and making those judgements consumes attention that the athlete would rather spend elsewhere.
A pacemaker instructed to run specific splits removes the decision entirely, and the athletes behind simply maintain contact.
This matters more than the physical saving in some races, because an even pace is more efficient than a variable one covering the same distance.
Why races without pacers look different
Championship races have no pacemakers, and they routinely produce slow early stages followed by a very fast finish.
Nobody wants to lead into the wind while carrying rivals along behind, so the field waits, and the result is a tactical race rather than a fast one.
This is why championship winning times are often well outside the best marks of the season, and the two are not really measuring the same thing. One rewards sustained speed, the other rewards judgement and a finishing kick.
The rules around them
Pacemakers are entered as competitors and must start the race properly, since an athlete who enters purely to assist without competing sits awkwardly against the rules.
Records set with pacing assistance are recognised in most disciplines, but certain forms of assistance, such as pacers entering mid-race, are not permitted.
Lights or displays around a track are used in some events as an alternative, providing the pacing information without providing the shelter.
The argument about their use
Critics say a paced race is a manufactured time trial and that comparing such marks with unpaced racing is misleading.
Supporters point out that the practice is transparent, available to everyone and long established, and that the alternative is slower racing rather than fairer racing.
The compromise most competitions have reached is to allow it while keeping championship racing free of it, so both kinds of contest continue to exist.
