The deformation spline is created when you initialize Physique. It is a continuous curve through several points. The deformation spline is a smooth curve that runs from joint to joint.
The deformation spline displays as a yellow curve that runs through the mesh.
The Bend, Bias, and Tension spinners can change the shape of the deformation spline. See Link Settings Rollout.
The deformation spline also takes into consideration twisting and scaling of the skeleton’s links. At the Link sub-object level, you take control of the behavior of the deformation spline, and subsequently gain full control of the skin’s behavior relative to the skeleton’s movement.