In classic spastic hypertonia (having extreme muscular tension), when a joint is moved passively, maximum resistance is felt after just a small movement. The more rapid the movement, the quicker and more pronounced the resistance. This classic form of spastic hypertonia is referred to as clasp-knife. In the most severe type of spastic hypertonia, the affected part will be rigid whether flexed or extended.
The symptoms associated with the spastic type of cerebral palsy lessen during sleep and are exacerbated by stress or voluntary movement.
