To create a finished realistic look some muscles should be added to the croquis. Muscles give the rounded, fleshed-out look to the different parts of the croquis. How large the muscles are drawn is a matter of personal preference, but normally, for the fashion croquis, minimal musculature is indicated: in fashion drawing the “look” is long and lean. (For drawings of active sportswear larger muscles can be shown).
In fashion drawing it is not necessary to show much anatomical detail (compared to medical drawing, for example). However it is appropriate and can be attractive to add some anatomical detail in the parts of the figure where it is most noticed, for example the contours of the collar bone (scapula), the roundness of the shoulder, the fullness of the bust, the shape of the ribcage, the softness of the tummy, the angularity of the knee. This anatomical detail is indicated using shading with appropriate levels of light and dark in the relevant parts. Note that muscles of both the legs and the arms are longer on the outside edges of the body than the inside.