Rigidity is one of the primary symptoms of Parkinson's disease and refers to stiffness and resistance to movement of a body part. Sometimes there is a jerky "cogwheel" phenomenon in an arm or leg when the doctor tries to move your limb around.
Rigidity also may occur in the neck, shoulders, hips and ankles. The stiffness and reduced range of motion may be painful. In fact, one of the earliest symptoms of PD for some people is stiffness and pain in the shoulder. For some persons with PD, rigidity of the neck and trunk (axial rigidity) may occur, resulting in a curving of the spine or a stooped posture and this stooped posture can cause additional stiffness and rigidity.
Source: Jankovic J. Parkinson's disease: clinical features and diagnosis. J Neurol Neurosurg Psychiatry. 2008 Apr;79(4):368-76. Review.
