A condition which may be due to a change in the joints, ligaments, tendons, or muscles, or to the influence of the nervous system over the muscles of the part affected. Stiffness is associated with various forms of arthritis or muscular disorders, and with the effects of injuries to joints, tendons and muscles. Stiffness of the neck muscles, resulting in bending the head backwards, and of the hamstring muscles, causing difficulty in straightening the lower limbs, may be a sign of MENINGITIS. Stiffness or spasticity also occurs in certain diseases of the central nervous system.