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.
The World Athletics U20 Championships is a biennial world championships for the sport of athletics organised by the World Athletics, contested by athletes in the under-20 athletics age category (19 years old or younger on 31 December in the year of the competition.
The Mixed 4 × 400 metres relay at the 2021 IAAF World U20 Championships was held at the Kasarani Stadium on 18 August.
The men's shot put at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 18 and 19 August.
The men's hammer throw at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 18 and 20 August.
The men's 800 metres at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 19, 21 and 22 August.
The women's 400 metres hurdles at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 19 and 22 August.
The men's 400 metres hurdles at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 19, 21 and 22 August.
The women's 800 metres at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium from 19 to 21 August.
The men's javelin throw at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 18 and 20 August.
The men's 100 metres at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 18 and 19 August.
The men's 1500 metres at the 2021 World Athletics U20 Championships will be held at the Kasarani Stadium on 19 and 21 August.
The women's 400 metres at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium 18 and 21 August.
The women's 200 metres at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 20 and 21 August.
The men's 110 metres hurdles at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 20 and 21 August.
The women's 100 metres hurdles at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 20 and 21 August.
The men's discus throw at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 21 and 22 August.
The men's 200 metres at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 20 and 21 August.
The men's 4 × 100 metres relay at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 21 and 22 August.
The men's 4 × 400 metres relay at the 2021 World Athletics U20 Championships was held at the Kasarani Stadium on 21 and 22 August.
