why not both? i think there was that one manga about this chubby guy coming across this one girl who wanted an 'ideal erotic' body so she gained weight AND put on muscle or so, not sure how much of it you can control but might depend on the type of exercises you do
(I assume they used birth control but missed opportunity/equally an amusing sitcom scene for her to have a bit of 'stomach flab'/protruding and him assuming she's pregnant lol)