musclebuilding vs muscle building

musclebuilding and muscle building both are nouns.

Word	Noun	Adjective	Verb	Adverb
musclebuilding	Yes	No	No	No
muscle building	Yes	No	No	No

As nouns, musclebuilding and muscle building are synonyms defined as:

musclebuilding and muscle building: exercise that builds muscles through tension

Other synonyms of musclebuilding include anaerobic exercise, bodybuilding.

musclebuilding (noun)	muscle building (noun)
exercise that builds muscles through tension	exercise that builds muscles through tension