What is “Fartlek Training”? Fartlek is a Swedish word and could be translated as a “speed game”. This is the name for interval training involving changes in intensive physical activity and active recovery periods. Fartlek training combines interim training and continuous running. Activities allow the runner to run the distance that fits at the speed that suits him, provided the intensity of effort changes at the right and specified intervals. What’s most important is to keep the good running form during the fartile, both fast and slow shares.