Though frustrating for the patient, it is rarely disabling. It usually disappears during sleep or improves with intentional movement. Initially, three-quarters of all patients experience the tremors in one part or on one side of the body. Later it may become more general. Most patients acknowledge that their tremors eventually led them to seek a physician's help.
Most patients also experience rigidity, or a resistance to movement.
All muscles in the human body associated with movement work smoothly in part because they have opposing muscles. When one muscle is activated, its opposing muscle relaxes. With Parkinson's disease, however, the brain's neurological signals to the muscles become confused, causing both sets of muscles to remain constantly tensed and contracted. This causes muscular rigidity and achiness. The person typically feels stiff or weak.