Rigidity, or a resistance to movement, is a Parkinson's disease
symptom seen in most people with this condition. A major principle of body movement is that all muscles have an opposing muscle. Movement is possible, not just because one muscle becomes more active, but also because the opposing muscle relaxes. In Parkinson's disease, rigidity comes about when, in response to signals from the brain, the delicate balance of opposing muscles is disturbed. The muscles remain constantly tensed and contracted so that the person aches or feels stiff or weak. The rigidity becomes obvious when another person tries to move the affected person's arm, which will move only in ratchet-like or short, jerky movements known as "cogwheel" rigidity.
Bradykinesia, or the slowing down and loss of spontaneous and automatic movement, is a particularly frustrating symptom of Parkinson's disease because it is unpredictable. One moment the person can move easily. The next moment, he or she may need help. This may well be the most disabling and distressing symptom of the disease because the person cannot rapidly perform routine movements. Activities once performed quickly and easily -- such as washing or dressing -- may take several hours.
Postural instability, or impaired balance and coordination, causes a person to develop a forward or backward lean and to fall easily. When bumped from the front or when starting to walk, a person with a backward lean has a tendency to step backwards, which is known as retropulsion.
Postural instability can cause a person to have a stooped posture, in which the head is bowed and the shoulders are drooped. As the disease progresses, walking may be affected. A person may halt in mid-stride and "freeze" in place, possibly even toppling over. Or, he or she may walk with a series of quick, small steps as if hurrying forward to keep balance. This is known as festination.