fartlek vs athletic training

fartlek and athletic training both are nouns.

Word	Noun	Adjective	Verb	Adverb
fartlek	Yes	No	No	No
athletic training	Yes	No	No	No

As nouns, athletic training is a hypernym of fartlek; that is, athletic training is a word with a broader meaning than fartlek:

fartlek: a method of athletic training (especially for runners) in which strenuous effort and normal effort alternate in a continuous exercise
athletic training: the course of practice and exercise and diet undertaken by an athlete

fartlek (noun)	athletic training (noun)
a method of athletic training (especially for runners) in which strenuous effort and normal effort alternate in a continuous exercise	the course of practice and exercise and diet undertaken by an athlete