The shadow of movement.

Movement is preceded, accompanied and followed by reactions which give to the primary action its correct execution and ensure that the body's axis, together with the limbs, maintains the right balance. If these reactions are interfered with, incoordination of movement, lack of balance, hypertonia or dystonia may all appear. In the case of dystonia, postural mechanisms tend to become dominant and take over from the kinetic component of movement. In the upper limbs, the dystonic posture follows patterns analogous to those used by monkeys for postural purposes. Thus, while the initial mechanisms of movement represent highly sophisticated processes thoroughly adapted to living in an upright state, the reactions that go with the movement are more primitive and probably have a less helpful role.