This contraction causes stiffness or tightness of the muscles that can affect movement, speech and walking.
Spasticity usually occurs as a result of damage to the portion of the brain or spinal cord that controls movement. It may occur in association with spinal cord injury (SCI), multiple sclerosis, cerebral palsy, damage to the brain because of lack of oxygen, brain trauma, severe head injury, and metabolic diseases such as adrenoleukodystrophy, amyotrophic lateral sclerosis (Lou Gehrig's disease), and phenylketonuria. Many people with SCIs experience spasticity.1
For people with SCI, spasticity occurs because axons in the spinal cord can not relay brain messages to control muscles, making them vulnerable to involuntary spasms. Most spinal-cord-injured persons have a healthy, intact spinal cord below the immediate area of their injury. In this situation, nerve impulses generated from below the area of injury reach muscles and cause a reaction. These impulses are not initiated or controlled by the brain; and so, can be both exaggerated and uncontrollable. Different sensory stimuli generated from below the level of SCI can cause spasticity. Examples include a change in body position (e.g., movement of an extremity), bladder irritation, pressure sores, fractured bones or a bowel movement.1