Spasticity is a condition that affects the muscles and ultimately interrupting normal movements patterns such as reaching with the arm or walking. During movement, our brain sends an impulse through the nervous system to the muscle we want to move. When the muscles on one side of the joint contract or tighten, the muscles on the opposite aspect of the joint may need to relax so that movement is accomplished.
If the messages from the brain or along the nerve pathways are interrupted, which can occur following a stroke or other brain injury, muscle activity and movement patterns may be disrupted. Low levels of muscle activity, also called low tone, may cause a limb to hang loosely in the joint, making an action such as reaching difficult or impossible. High levels of muscle activity, also called high tone, can create overactive muscles that lack the ability to coordinate motion.
Spasticity can also be described as velocity-dependent, meaning that quick movements of the muscles activate increased muscle activity or tone. The muscle on the opposite side of the joint does not relax, creating difficulty with movement.
Spasticity can also be influenced by a patient developing an infection, or by common changes in weather or temperature. If untreated, the muscle tightness can lead to stiff joints that are difficult to stretch and move. Physical therapy, medications, and in more severe cases, surgery, is used to manage spasticity.