The 400 metres, or 400 metre dash, is a common sprinting event in track and field competitions. It has been featured in the athletics programme at the Summer Olympics since 1896 (1964 for women). On a standard outdoor running track, it is exactly 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 the length of a quarter of a mile and was referred to as the 'quarter-mile'—instead of the 400 m (437.445 yards), though this distance is now obsolete. An athlete who competes in the 400 m may still be referred to as 'quarter-miler'.
Maximum sprint speed capability is a significant contributing factor to success in the event, but athletes also require substantial speed endurance and the ability to cope well with high amounts of lactic acid to sustain a fast speed over a whole lap. While considered to be predominantly an anaerobic event, there is some aerobic involvement and the degree of aerobic training required for 400 metre athletes is open to debate.