heftiness vs muscularity

heftiness and muscularity both are nouns.

Word	Noun	Adjective	Verb	Adverb
heftiness	Yes	No	No	No
muscularity	Yes	No	No	No

As nouns, heftiness and muscularity are synonyms defined as:

Other synonyms of heftiness include brawn, brawniness, muscle, sinew.

heftiness (noun)	muscularity (noun)
possessing muscular strength	possessing muscular strength
the property of being large in mass	an imaginative lively style (especially style of writing)
	the physiological state of having or consisting of muscle