Spasticity and rigidity are common symptoms of central nervous system injuries, such as spinal cord injury and Parkinson's disease, and result in distinct patterns of increased resistance during passive joint movements. Spasticity is characterized by a velocity-dependent increase in stretch reflexes, accompanied by exaggerated tendon responses, while rigidity is marked by consistent resistance throughout the range of motion, traditionally considered independent of stretch velocity. However, recent studies suggest that rigidity may also be influenced by stretch velocity. This study aims to investigate muscle tone by examining spasticity, rigidity, and normal muscle function through neural and biomechanical changes. Standard clinical tools, such as the Modified Ashworth Scale and Unified Parkinson's Disease Rating Scale, along with additional assessments like the Myoton and Post-Activation Depression (PAD), will be employed.