What is the main difference between rigidity and spasticity?

See below: It is mostly the quality of the movement. With rigidity, the muscle tone stays pretty much the same when someone moves the limb, there is constant resistance to movement. It has also been called "lead pipe" rigidity. In spasticity, there is initial resistance to movement and then the resistance gives way. This is called "clasp-knife" spasticity. Rigidity is often seen in parkinsons.