The 400 metres, or 400 metre dash, is a sprinting 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 and was referred to as the 'quarter-mile'—instead of the 400 m (437.445 yards), though this distance is now obsolete.
Like other sprint disciplines, the 400 m involves the use of starting blocks. The runners take up position in the blocks on the 'ready' command, adopt a more efficient starting posture which isometrically preloads their muscles on the 'set' command, and stride forwards from the blocks upon hearing the starter's pistol. The blocks allow the runners to begin more powerfully and thereby contribute to their overall sprint speed capability. 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.