Do not use pectorals size alone as a determinant for this tag. It is common in artwork to draw them unproportional to the rest of the body, especially with manboobs etc.
Examples
Muscular
Plump muscular
If the physique is muscular with a belly like many wrestlers and bodybuilders, consider adding the plump, belly and/or strongman waist tag as well.
Toned physique
If the character has an athletic build that’s not overly bulky, use toned instead. Do not use muscular with the toned tag when describing one character.
