Impaired anticipatory control of isometric forces during grasping by children with cerebral palsy.

The authors examined the force regulation during prehension of 12 children with cerebral palsy (CP) and an age-matched control group. The control group appropriately scaled the isometric force output in one force-rate pulse toward the weight of the previously lifted object, but children with CP exhibited stepwise increases in force in which the force amplitudes were not influenced by the object's weight. When the object was held in the air, most children with CP were able to modify their force output according to the object's weight, using sensory feedback, but their forces were more variable than those of the control group and less influenced by the object's weight. Although children with CP have disturbed sensory feedback--likely to lead to an indistinct internal representation of an object's physical properties--their main disability stems from impaired central co-ordination of motor activity.