Final answer:
Parkinson's disease is a degenerative disorder that affects the muscles, causing them to become stiff and leading to a stooped posture and a shuffling gait.
Step-by-step explanation:
Parkinson's disease is a degenerative disorder of the central nervous system that mainly affects the muscular system and movement. It is characterized by four motor signs and symptoms: muscle tremor (shaking), muscle rigidity, slowness of movement, and postural instability. The disease causes the muscles to become stiff, leading to a stooped posture and a shuffling gait.