Old English faran "to journey, set forth, go, travel, wander, make one's way," also "be, happen, exist; be in a particular condition," from Proto-Germanic *faranan "to go" (source also of Old Saxon, Old High German, Gothic faran, Old Norse and Old Frisian fara, Dutch varen, German fahren), from PIE *por- "going, passage," from root *per- (2) "to lead, pass over." Related: Fared; faring.
Proto-Indo-European root meaning "to lead, pass over." A verbal root associated with *per- (1), which forms prepositions and preverbs with the basic meaning "forward, through; in front of, before," etc.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit parayati "carries over;" Greek poros "journey, passage, way," peirein "to pierce, pass through, run through;" Latin portare "to carry," porta "gate, door," portus "port, harbor," originally "entrance, passage," peritus "experienced;" Avestan peretush "passage, ford, bridge;" Armenian hordan "go forward;" Old Welsh rit, Welsh rhyd "ford;" Old Church Slavonic pariti "to fly;" Old English faran "to go, journey," Old Norse fjörðr "inlet, estuary."
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Definitions of fartlek
a method of athletic training (especially for runners) in which strenuous effort and normal effort alternate in a continuous exercise;