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)—also referred to as the 'quarter-mile'—instead of the 400 m, 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. Whilst 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.^{[citation needed]}

LaShawn Merritt (born June 27, 1986) is an American track and field athlete who competes in sprinting events, specializing in the 400 meters. He is the reigning Olympic champion over the distance and his personal best of 43.75 seconds makes him the fifth fastest of all time. In October 2010 he was suspended for 21 months for failing a doping test.

He was a successful junior athlete and won the 400 m gold at the 2004 World Junior Championships in Athletics, as well as setting two world junior records in the relays. He became part of the American 4×400 meter relay team and helped win the event at the 2006 IAAF World Indoor Championships. He established himself individually in 2007 by winning a silver medal in the 400 m at the 2007 World Championships.

He came out on top of a rivalry with Jeremy Wariner in 2008 by winning in the 2008 Olympic final in a personal best time, and by a record margin. He also broke the Olympic record in the relay with the American team, recording the second fastest time ever. Merritt established himself as the World Champion with a win at the 2009 World Championships in Athletics in the 400 m and the 4×400 m relay. He failed three drugs tests in the winter of 2009–2010, testing positive for the banned steroid Dehydroepiandrosterone, which he had allegedly consumed through the use of a penis enlargement drug. He accepted a two year ban from the sport.

Jehue Gordon (born 15 December 1991) is a Trinidadian track and field athlete who specialises in the 400 metres hurdles. He turned professional on June 24, 2010, and signed a deal with Adidas in August 2010.

He began his international athletics career at the 2008 World Junior Championships in Athletics, where he finished fifth in the semi-finals at the age of 16. He was the bronze medallist in the 400 m hurdles at the 2008 CARIFTA Games and went on to win the gold medal the following year, recording a championship record of 50.01 seconds. His success continued in the form of a bronze medal at the 2009 Central American and Caribbean Championships in Athletics, where he ran a time of 49.45 seconds, and a silver at the 2009 Pan American Junior Athletics Championships.

He qualified for the 2009 World Championships in Athletics and surprised by setting a world-age best and senior national record of 48.66 seconds in the heats. He progressed through the rounds and reached the final, finishing in fourth with a 48.26-second national record. Statisticians A. Lennart Julin and Mirko Jalava picked out Gordon's performances as sign of promise for future success. At the start of the 2010 season, he took a 400 m and 110 metres hurdles double at the trials for the CARIFTA Games. He went on to improve the championship records in both the 110 and 400 m hurdles at the 2010 CARIFTA Games, earning himself that year's Austin Sealy Trophy.

Christine Ijeoma Ohuruogu MBE (born 17 May 1984) is a British athlete, who specialises in the 400 metres; the event for which she is the current Olympic and former World and Commonwealth Champion. Her victory in the Beijing Games was the 50th gold medal for Great Britain in Athletics at the Olympics.

Ohuruogu's Personal Best of 49.61 ranks her third amongst British women 400 m runners, behind fellow Olympic medallists Kathy Cook and Katharine Merry.

Born to Igbo Nigerian parents in Newham, east London, she was raised less than one mile from the 2012 Summer Olympics stadium in Stratford. Ohuruogu studied at University College London, where she graduated in Linguistics in 2005. She also played netball during her undergraduate studies. Christine has 8 siblings, one of whom is Victoria Ohuruogu, a top sprints competitor in her age group. She also went to St. Edwards Church of England School, Romford, Essex and Trinity Catholic High School, Woodford Green, Essex.

Ohuruogu is a member of Newham and Essex Beagles Athletics Club.

Amantle Montsho (born July 4, 1983 in Mabudutsa, Ngamiland, Botswana) is a female sprinter from Botswana who specializes in the 400 metres. She represented her country at the 2004 and 2008 Summer Olympics, reaching the final at the latter edition. She has also competed at the World Championships in Athletics and the IAAF World Indoor Championships, and is currently the World Champion over the 400m, winning in a personal best time of 49.56 in Daegu.

A two-time African Championships gold medallist over 400 m, she has also won titles in the event at the 2007 All-Africa Games, the 2010 IAAF Continental Cup and the 2010 Commonwealth Games. Her Commonwealth win made her Botswana's first ever gold medallist of the games.

Her personal best times are 11.60 seconds in the 100 m, 22.94 seconds in the 200 metres and 49.56 seconds in the 400 m. She trains at the High Performance Training Centre in Dakar, Senegal. She holds the national record for the 400 m both indoors and outdoors.

She has competed at the 2004 Olympic Games, the 2006 Commonwealth Games and the World Championships in 2005 and 2007 without reaching the finals.