400 metres

The 400 metres, or 400-meter dash, is a sprint event in track and field competitions. It has been featured in the athletics programme at the Summer Olympics since 1896 for men and since 1964 for women. On a standard outdoor running track, it is one lap around the track. Runners start in staggered positions and race in separate lanes for the entire course. In many countries, athletes previously competed in the 440-yard dash (402.336 m)—which is a quarter of a mile (1,760 yards) and was referred to as the "quarter-mile"—instead of the 400 m (437.445 yards), though this distance is now obsolete.

The current men's world record and Olympic record is held by Wayde van Niekerk of South Africa; his time of 43.03 seconds is the fastest 400 m ever run, in either an open 400 m or a relay split (excluding reaction time). While Michael Johnson holds the fastest 400 m relay split with a time of 42.94, relay splits are typically faster because athletes have a running start and do not need to react to the gun if they are not the leadoff leg. Considering van Niekerk's reaction time of 0.181 seconds in his run of 43.03, van Niekerk covered the 400-metre distance itself in 42.85 seconds, therefore being 0.09 seconds faster than Johnson's relay split.