Artists may be excellent in their craft but they, too, have their limits. They usually try to get references for their drawings for a more lifelike appearance. Some will hire models to pose for them while others will use themselves.
They might stand in front of a mirror to analyze the contours of the body. They might dress in a certain way to see how the fabric folds and flows. They could snap pictures to hold the pose without strain.
It is important to note the differences in the figures of males and females. A female drawing reference will typically have wider hips, slender shoulders, bigger chests, and smaller stature than the male counterpart.
Of course, these are only for the stereotypes as real bodies span a wide range of shapes and sizes for both sexes. It is crucial for artists to find the right kind of reference for their purpose.