Long-distance running only the placing is of importance. Other less popular variants such as fell running, trail running, mountain running and tower running combine the challenge of distance with a significant incline or change of elevation as part of the course. Multisport races frequently include endurance running. Triathlon, as defined by the International Triathlon Union, may feature running sections ranging from five kilometres (3.1 mi) to the marathon distance (42.195 kilometres, or 26 miles and 385 yards), depending on the race type. The related sport of duathlon is a combination of cycling and distance running. Previous versions of the modern pentathlon incorporated
2012 Olympic Marathon Course as 42.195 km and specifically state that the course must not be less than this distance. The rules further state that in Olympic competition the standard distance may not be exceeded by more than 0.1%. In order for a marathon performance to be ratified as a world record by the IAAF, the course must also meet other criteria that rule-out "artificially fast times" produced on courses aided by downhill slope or tailwind: the distance between start and end points when measured in a straight line should not exceed 50% of the length of the course (21.092 km in the case