Rigidity is one of the main symptoms of Parkinson’s and indications of its onset include aching muscles and muscle stiffness or weakness. Rigidity is often associated with slowness of movement (bradykinesia).
In the early stages of Parkinson’s, rigidity may be present in one arm and later progress to the leg on the same side, then move to the trunk and the other side of the body. Be aware, however, that every case of Parkinson’s is unique and symptoms develop at different rates in different people. Rigidity will progress faster in some people than in others.
Rigidity tends to be predominant in flexor muscles of the trunk and limbs, leading to change in posture with the elbows and knees being flexed and the trunk bent forwards. This results in the familiar, stooped Parkinson’s posture. As rigidity becomes more prominent it affects the way people perform activities and tasks in daily life, from the way they get out of bed to the way they eat or write.
What causes rigidity in Parkinson’s?
The increased tensing of the muscles is thought to occur due to the excessive and poorly controlled drive of motor neurons in the brain. Reduced dopamine levels are probably responsible for this over-activity of the motor neurons, which are normally inhibited. This leads to the inability to fully relax the muscles and the normal agonists-antagonists interplay is disrupted. Furthermore, the excessive drive of the motor neurons causes muscle fibres to alter their visco-elastic properties, and the result of this change in composition may contribute to the increased resistance during passive stretches of the limbs.
