Rigidity is caused by a patient's muscles being continuously contracted. Two muscle groups are generally required to work together to create motion. One muscle group is relaxed, while the other is contracted. Since both muscle groups are contracted during rigidity, no movement occurs. Since the muscles are always working or contracted, the patient's muscles might ache and feel stiff.
Rigidity can also cause the patient's face to look emotionless.
Another symptom of Parkinson's disease is bradykinesia, the slowing, or loss, of spontaneous and automatic movement. It is caused by the brain's slowness in transmitting the necessary instructions to the appropriate parts of the body. This symptom is unpredictable and ranges from non-existant to highly debilitating. Bradykinesia can cause the patient to take an excessive amount of time performing routine tasks. Another similar symptom, akinesia, also involves difficulty in initiating voluntary movements.