Rigidity

Rigidity refers to increased resistance to passive movement, throughout the whole movement, independent of the velocity of the movement (unlike spasticity, which is velocity-dependent and occurs not throughout the whole movement). Rigidity is seen in parkinsonsism and neuroleptic malignant syndrome. Rigidity is better observed when passive movement is performed slowly.

Cogwheel rigidity is the most common form of rigidity, where the passive movement is periodically interrupted by resistance, causing the muscles to "jerk" throughout the movement, which feels somewhat like a cogwheel.