events have their roots in races of imperial measurements which were later altered to metric: the 100 m evolved from the 100-yard dash, the 200 m distances came from the furlong (or 1/8 of a mile), and the 400 m was the successor to the 440-yard dash or quarter-mile race. At the professional level, sprinters begin the race by assuming a crouching position in the starting blocks before leaning forward and gradually moving into an upright position as the contest progresses and momentum is gained. Athletes remain in the same lane on the running track throughout all sprinting events, with the sole exception of the 400 m indoors. Races up to 100 m are largely focused upon acceleration to an athlete's maximum speed. All sprints beyond this distance increasingly incorporate an element of endurance. Human physiology dictates that a runner's near-top speed cannot be maintained for more than thirty seconds or so as lactic acid builds up, and leg muscles begin to be deprived of oxygen. The 60 metres is a common indoor event and it an indoor world championship event. Other less-common events include the 50 metres, 55 metres, 300 metres and 500 metres which are used in some high and collegiate competitions in the United States. The 150 metres, is rarely competed: Pietro Mennea set a world best in 1983, Olympic champions Michael Johnson and Donovan Bailey went head-to-head over the distance in 1997, and Usain Bolt improved Mennea's record in 2009. Middle distance Middle-distance running events are track races longer than sprints up to 3000 metres. The standard middle distances are the 800 metres, 1500 metres and mile run, although the 3000 metres may also be classified as a middle-distance event. The 880-yard run, or half-mile, was the forebear to the 800 m distance and it has its roots in competitions in the United Kingdom in the 1830s. The 1500 m came about as a result of running three laps of a 500 m track, which was commonplace in continental Europe in the 1900s. Long distance Examples of longer-distance running events are long-distance track races, half marathons, marathons, ultramarathons, and multiday races. See also Global Running Day Level and incline running List of people killed while running Outline of running Plogging Running energetics Trail running Ultra Running Skyrunning References Further reading External links Articles containing video clips Endurance games Terrestrial locomotion