How it works
Competitors run once around a 400m track. They start from blocks set in staggered positions and run in lanes.
A reaction time – measured by sensors in the starting pistol and on the blocks – of less than 0.1 is deemed a false start and runners will be recalled, and the responsible athlete disqualified. A runner can also be disqualified if he or she steps out of their designated lane.
One of the original events at the Ancient Olympics was the 'diaulos', a race around two marks on a course roughly equivalent to the current 400m.
The 400m for men has been in every Olympic Games since 1896. Women first contested the distance at the 1964 Tokyo Games.
Did you know
When Cathy Freeman won Olympic gold in the 400m at her home Games in Sydney 2000, it drew record TV audiences in Australia of about 7,000,000 viewers.
This is arguably the strongest event for US men, having won 20 of the 27 Olympic titles to date. But their female counterparts have won just two Olympic golds.
The first man to win the Olympic 400m twice (and the only man to win the 400m and 200m at the same Games), Johnson is the greatest one-lap runner. The Texan took gold in the Atlanta (1996) and Sydney (2000) Games. He also won four world titles, and in 1999 set a world record of 43.18 that still stands today.
France’s Perec was the first runner of either gender to win Olympic gold twice in the 400m, crushing the opposition at the 1992 Barcelona and 1996 Atlanta Games – where, like Johnson, she performed a double by snatching 200m glory, too. Long-legged and graceful, she also won two world titles.