muscle system vs muscular structure

muscle system and muscular structure both are nouns.

Word	Noun	Adjective	Verb	Adverb
muscle system	Yes	No	No	No
muscular structure	Yes	No	No	No

As nouns, muscle system and muscular structure are synonyms defined as:

muscle system and muscular structure: the muscular system of an organism

Other synonyms of muscle system include musculature.

muscle system (noun)	muscular structure (noun)
the muscular system of an organism	the muscular system of an organism