tonic contraction n.
The sustained contraction of a muscle, as is necessary for maintaining posture.
The sphincter ani is constantly in a state of tonic contraction, but the force of its contraction may be voluntarily increased.
The sphincter is kept in a state of tonic contraction by a nervous centre situated in the lumbar portion of the spinal cord.
This affection consists in spasmodic closure of the outlet from the bladder by tonic contraction of the circular muscular fibers.
tonic contraction of the diaphragm is nearly always of an hysterical nature, and is doubtless akin to the aerophagic type.