GO:0014820:   tonic smooth muscle contraction
A process in which force is generated within tonic smooth muscle tissue, resulting in a change in muscle geometry. Force generation involves a chemo-mechanical energy conversion step that is carried out by the actin/myosin complex activity, which generates force through ATP hydrolysis. In the tonic smooth muscle, the muscle contraction occurs without an ordered sarcomeric structure. Tonic smooth muscle contraction occurs as a sustained continuous contraction.