isometric exercise vs workout

isometric exercise and workout both are nouns.

Word	Noun	Adjective	Verb	Adverb
isometric exercise	Yes	No	No	No
workout	Yes	No	No	No

As nouns, workout is a hypernym of isometric exercise; that is, workout is a word with a broader meaning than isometric exercise:

isometric exercise: muscle-building exercises (or a system of musclebuilding exercises) involving muscular contractions against resistance without movement (the muscles contracts but the length of the muscle does not change)
workout: the activity of exerting your muscles in various ways to keep fit

Other hypernyms of isometric exercise include exercise, exercising, physical exercise, physical exertion.

isometric exercise (noun)	workout (noun)
muscle-building exercises (or a system of musclebuilding exercises) involving muscular contractions against resistance without movement (the muscles contracts but the length of the muscle does not change)	the activity of exerting your muscles in various ways to keep fit