Fartlek, a Swedish running method that mixes fast and slow paces, translates into English as “speed play.” The Swedish word combines fart, meaning “speed,” with lek, meaning “play.” Despite its amusing appearance to English speakers, the term has nothing to do with flatulence.
Swedish coach Gösta Holmér developed Fartlek in the late 1930s for Sweden’s cross-country runners. His approach blended continuous running with faster efforts and easier recovery periods, often across forests, hills, and other natural terrain. The runner could vary pace by feel rather than follow exact track-based intervals.
That flexibility distinguishes traditional Fartlek from formal interval training. Intervals usually prescribe precise distances, times, and recovery periods, while a Fartlek session might involve sprinting between trees, running hard up a hill, or accelerating for a chosen stretch of road. Modern workouts may be highly structured, but the original idea emphasized changing pace continuously and naturally.
Fartlek can also be adapted beyond running, including cycling and field sports, whenever athletes need repeated changes between hard and easy effort.