In multiple sclerosis, the myelin, or protective coating of the nerves is being injured. As myelin is damaged in the part of the central nervous system that controls voluntary movement, spasticity is often the result. The damage disrupts important signals between the brain and the muscles.
Spasticity refers to muscle stiffness and a wide range of involuntary muscle spasms (sustained muscle contractions or sudden movements). It is one of the more common symptoms of MS.
Spasticity may be as mild as the feeling of tightness of muscles or may be so severe as to produce painful, uncontrollable spasms of extremities, usually of the legs. Spasticity may also produce feelings of pain or tightness in and around joints, and can cause low back pain. Although spasticity can occur in any limb, it is more common in the legs. Sometimes spasticity is so severe that it gets in the way of daily activities and sleep.
I have found that some degree of spasticity helps me. For those of us who experience significant leg weakness, the spasticity gives my legs some rigidity, making it easier for me to stand, transfer, or walk.
Sitting for too long increases my spasticity symptoms, as does severe weather conditions. High heat makes my legs turn into noodles and in the freezing cold I have a hard time bending my knees to climb into the car.