Spasticity can occur either as a sustained stiffness caused by increased muscle tone or as spasms that come and go, especially at night.When individuals are first injured, their muscles are weak and flexible because of what’s called spinal shock: the body’s reflexes are absent below the level of injury; this usually lasts for a few weeks or several months. Once the spinal shock is over, reflex activity returns.


Since the normal flow of nerve messages below the level of injury is interrupted, those messages may not reach the reflex center of the brain. The spinal cord then attempts to moderate the body’s response. Because the spinal cord is not as efficient as the brain, the signals that are sent back to the site of the sensation are often over exaggerated. This is an overactive muscle response referred to by doctors as spastic hypertonia (SH): uncontrollable “jerking” movement, stiffening or straightening out of muscles, shock-like contractions of a muscle or group of muscles, and abnormal tone in the muscles.