Top runners as well as amateurs are increasingly forgoing the road and the track in favour of a more unusual challenge – from crossing entire countries to circling motorway gyratories …

The idea is simple: a runner sets out to cover a given route or journey faster than the previous known best. For elites, this usually means tackling an iconic trail or point-to-point run, many of which have well-established FKTs. In America, where the trend is most marked, one acronym has given rise to many more: to set a fastest known time for the JMT (John Muir Trail) or the R2R (the “rim-to-rim” width of the Grand Canyon) would carry all the prestige of winning a major trophy

Source: Forever running: the rise and rise of the fastest known time | Life and style | The Guardian