Parkinson's disease is a progressive brain disorder that causes a gradual loss of muscle control. Its symptoms include tremors, stiffness, slowed movements, and poor balance. Early signs may include slight shaking, difficulty walking or writing, and stooped posture. Treatments include medications like dopamine agonists and surgeries like deep brain stimulation. Physical therapy focuses on exercises to improve mobility, balance, posture, and prevent contractures. Symptoms fluctuate between "on" and "off" periods depending on dopamine levels, affecting the appropriate exercises.