brawniness vs heftiness

brawniness and heftiness both are nouns.

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

As nouns, brawniness and heftiness are synonyms defined as:

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

brawniness (noun)	heftiness (noun)
possessing muscular strength	possessing muscular strength
	the property of being large in mass