The 400m starts with a staggered bend, with athletes running a full circuit of the track.
The competition starts with heats. The number of heats and the number of athletes progressing to the next round depends on the number of athletes competing. In each heat the fastest athletes go through, as well as a set number of the fastest losers across all the heats. The following rounds run on the same format, until eight athletes are through to compete in the final.
The draw to determine which heat athletes run in is decided by their initial seedings (based on previous performance) for the first round, and then their performances after that. This ensures that the highest seeded athletes are not drawn in the same heat.
In the first round, an athlete’s lane allocation is drawn by lot, and in subsequent rounds it is dependent on their performance. The highest-seeded athletes are drawn in the centre lanes.
Keys to success
In sprint races, the time separating athletes can be as little as one hundredth of a second, requiring a photo finish. A good start is crucial, as is technique while running and the quality of the finish. The winning athletes must be relaxed but perfectly focused on their race.
Breaking the rules
The most dramatic error for spectators, and arguably the most cruel for athletes, is the false start. Once in the set position on the blocks, any athlete moves off the starting blocks either before the gun has fired or within 0.10 sec of the gun firing is disqualified. Athletes can also be penalised for running out of their lane or obstructing another athlete.
Find out more about Men’s 400m and Women's 400m competitions at the Olympic Games on the International Olympic Committee website.