Rigidity is stiffness and resistance to limb movement caused by increased muscle tone, an excessive and continuous contraction of muscles.[1] In parkinsonism, the rigidity can be uniform, known as "lead-pipe rigidity," or ratchety, known as "cogwheel rigidity."[2][31][34][35] The combination of tremor and increased tone is considered to be at the origin of cogwheel rigidity.[36] Rigidity may be associated with joint pain; such pain being a frequent initial manifestation of the disease.[31] In early stages of Parkinson's disease, rigidity is often asymmetrical and it tends to affect the neck and shoulder muscles prior to the muscles of the face and extremities.[37] With the progression of the disease, rigidity typically affects the whole body and reduces the ability to move.