Why is my weight painting 3D model stiff?

Your 3D model’s weight painting is stiff mainly due to uneven vertex weight distribution or missing smooth blending between bones. Stiffness happens when a vertex is fully assigned to one bone (no gradual falloff)—it can’t move with adjacent bones, making movements like elbow bends feel rigid instead of natural. Fix it by using a soft brush or falloff tool to smooth weights around joints: ensure vertices near connections (e.g., knees, elbows) are shared between two relevant bones—this small adjustment adds flexibility to movements.