[3] Since it relies on a single neutral pose, it cannot effectively capture dynamic changes in muscle bulging, skin stretching, or the visibility of bones during movement—such as when an elbow bends.
Additionally, skeletal animation often struggles with maintaining volume, especially in areas like the elbows and shoulders, where bending joints can cause undesirable deformations.
Instead of relying solely on the skeleton's deformation, PSD adds corrective shapes on top of the skeletal animation to account for changes like muscle bulging, joint protrusion, or the preservation of volume around complex areas like the armpits and elbows.
[3] Artists can sculpt these additional poses to ensure that, for example, muscles bulge appropriately when the arm is flexed, or the elbow maintains its proper shape when bent.
This combination of skeletal animation and pose-based correction significantly enhances the realism of character movement, especially in areas where volume and surface detail are crucial.