Topology causes 3D models to be stiff in animation mainly when edge flow doesn’t match a character’s natural movement or joints lack deformation loops.
Poor topology (e.g., random triangles, missing loops at elbows/knees) prevents the mesh from stretching or compressing smoothly—this makes bends look rigid instead of fluid. For example, a character’s arm with no elbow loops will “pop” or stay stiff when bent, not deforming like real skin.
Fix this by having edge loops follow muscle and joint lines—this helps rigging tools distribute weight evenly, letting the model move naturally.