100 metres

Start

At the start, some athletes play psychological games such as trying to be last to the starting blocks.

At high level meets, the time between the gun and first kick against the starting block is measured electronically, via sensors built in the gun and the blocks. A reaction time less than 0.1 s is considered a false start. The 0.2-second interval accounts for the sum of the time it takes for the sound of the starter's pistol to reach the runners' ears, and the time they take to react to it.

For many years a sprinter was disqualified if responsible for two false starts individually. However, this rule allowed some major races to be restarted so many times that the sprinters started to lose focus. The next iteration of the rule, introduced in February 2003, meant that one false start was allowed among the field, but anyone responsible for a subsequent false start was disqualified.

This rule led to some sprinters deliberately false-starting to gain a psychological advantage: an individual with a slower reaction time might false-start, forcing the faster starters to wait and be sure of hearing the gun for the subsequent start, thereby losing some of their advantage. To avoid such abuse and to improve spectator enjoyment, the IAAF implemented a further change in the 2010 season – a false starting athlete now receives immediate disqualification. This proposal was met with objections when first raised in 2005, on the grounds that it would not leave any room for innocent mistakes. Justin Gatlin commented, "Just a flinch or a leg cramp could cost you a year's worth of work." The rule had a dramatic impact at the 2011 World Championships, when current world record holder Usain Bolt was disqualified.

Mid-race

Runners normally reach their top speed just past the halfway point of the race and they progressively decelerate in the later stages of the race. Maintaining that top speed for as long as possible is a primary focus of training for the 100 m. Pacing and running tactics do not play a significant role in the 100 m, as success in the event depends more on pure athletic qualities and technique.

Finish

The winner, by IAAF Competition Rules, is determined by the first athlete with his or her torso (not including limbs, head, or neck) over the nearer edge of the finish line. When the placing of the athletes is not obvious, a photo finish is used to distinguish which runner was first to cross the line.

Climatic conditions

Climatic conditions, in particular air resistance, can affect performances in the 100 m. A strong head wind is very detrimental to performance, while a tail wind can improve performances significantly. For this reason, a maximum tail wind of 2.0 m/s is allowed for a 100 m performance to be considered eligible for records, or "wind legal."

Furthermore, sprint athletes perform better at high altitudes because of the thinner air, which provides less air resistance. In theory, the thinner air would also make breathing slightly more difficult (due to the partial pressure of oxygen being lower), but this difference is negligible for sprint distances where all the oxygen needed for the short dash is already in the muscles and bloodstream when the race starts (explaining why many athletes choose not to breathe for the duration of the race). While there are no limitations on altitude, performances made at altitudes greater than 1000 m above sea level are marked with an "A."

Sex and ethnicity

Only male sprinters have beaten the 100 m 10-second barrier, nearly all of them being of West African descent. Namibian (formerly South-West Africa) Frankie Fredericks became the first man of non-West African heritage to achieve the feat in 1991 and in 2003 Australia's Patrick Johnson (an Indigenous Australian with Irish heritage) became the first sub-10-second runner without an African background.

In the Prefontaine Classic 2015 Diamond League meet at Eugene, Su Bingtian ran a time of 9.99 seconds, becoming the first Asian athlete to officially break the 10-second barrier. In the 2015 Birmingham Grand Prix Diamond League meet, British athlete Adam Gemili, who is of mixed Iranian and Moroccan descent, ran a time of 9.97 seconds on home soil, becoming the first athlete with either North African or Middle Eastern heritage to break the ten-second barrier. Of the six men's continental record holders, currently three of them were born in Nigeria.

It is believed that biological factors may be largely responsible for the notable success in sprinting events enjoyed by athletes of West African descent. This includes:

Top sprinters of differing ancestry, such as Christophe Lemaitre, are believed to be exceptions in that they too likely have the genes favourable for sprinting. Colin Jackson, an athlete with mixed ethnic background and former world record holder in the 110 metre hurdles, noted that both his parents were talented athletes and suggested that biological inheritance was the greatest influence, rather than any perceived racial factor. Furthermore, successful black role models in track events may reinforce the racial disparity.

Record performances

Major 100 m races, such as at the Olympic Games, attract much attention, particularly when the world record is thought to be within reach.

The men's world record has been improved upon twelve times since electronic timing became mandatory in 1977. The current men's world record of 9.58 s is held by Usain Bolt of Jamaica, set at the 2009 World Athletics Championships final in Berlin, Germany on 16 August 2009, breaking his own previous world record by 0.11 s. The current women's world record of 10.49 s was set by Florence Griffith-Joyner of the US, at the 1988 United States Olympic Trials in Indianapolis, Indiana, on 16 July 1988 breaking Evelyn Ashford's four-year-old world record by .27.

Some records have been marred by prohibited drug use – in particular, the scandal at the 1988 Summer Olympics when the winner, Canadian Ben Johnson was stripped of his medal and world record.

Jim Hines, Ronnie Ray Smith and Charles Greene were the first to break the 10-second barrier in the 100 m, all on 20 June 1968, the Night of Speed. Hines also recorded the first legal electronically timed sub-10 second 100 m in winning the 100 metres at the 1968 Olympics. Bob Hayes ran a wind-assisted 9.91 seconds at the 1964 Olympics.

Continental records

Updated 5 July 2015.

All-time top 25 men

As of 4 July 2016:

All-time top 25 women

As of June 2016

Top 10 Junior (under-20) men

Updated 16 April 2016

Top 10 Junior (under-20) women

Updated 25 July 2015

Top 10 Youth (under-18) boys

Updated 3 June 2016

Top 10 Youth (under-18) girls

Updated 20 June 2015

Paralympic men

Updated to 1 January 2015

Paralympic women

Updated to October 2015