Spasticity is a condition in which muscles are tight or stiff. At times the muscles may jerk or spasm uncontrollably. It can interfere with your ability to move, speak, or walk. Spasticity usually occurs because of damage to the part of the brain or spinal cord that controls voluntary movement. It is often the result of a spinal cord injury, a stroke, or a disease such as multiple sclerosis, cerebral palsy, or amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease).

The main treatments are physical therapy and medicines that reduce muscle spasms. If spasticity isn't treated, the muscles may freeze in an abnormal position.