Swedish exercise to evacuate area in an escape of wind?

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1952, Swedish, from fart "speed" (cognate with Old Norse fara "to go, move;" see fare (v.)) + lek "play" (cognate with Old Norse leika "play;" see lark (v.)).

WordNet Word definitions in WordNet
n. a method of athletic training (especially for runners) in which strenuous effort and normal effort alternate in a continuous exercise

Wiktionary Word definitions in Wiktionary
n. An athletic training technique, used especially in running, in which periods of intense effort alternate with periods of less strenuous effort in a continuous workout.

Wikipedia Word definitions in Wikipedia
Fartlek , which means "speed play" in Swedish , is a training method that blends continuous training with interval training . Fartlek runs are a very simple form of a long distance run. Fartlek training “is simply defined as periods of fast running intermixed ...