How do we differentiate spasticity and rigidity? what are the differences?

See below: Look at the muscle effect of spasticity to be similar to a pocket knife where there is a catch-like phenomenon, and the signs involve the antigravity muscles, like the leg extensors. Rigidity, like parkinson's is constant, on both flexion and extension, and no sudden catch can be exhibited.

Velocity dependent: Spasticity is velocity dependent- the faster you try to move the limb the more resistance you will encounter. Rigidity is a fixed resistance not affected by speed.