Using balance perturbations that challenged children with CP to the limits of their balance abilities effectively identified age performance differences and differences compared to typically developing children. Implications for rehabilitation programs are presented.

This study aimed to test mechanisms underlying impairments in balance control in children with cerebral palsy. We hypothesized that balance loss during large/fast perturbations could be due to reduced contraction of agonist muscles, delay in muscle contraction or simultaneous contraction of antagonist muscles, reducing the efficiency of the agonist burst. Electromyograms were recorded as children recovered from balance threats of varying magnitudes/velocities. In typically developing children muscle response magnitudes increased with larger/faster perturbations, while in children with cerebral palsy they did not. There was no difference in muscle onset latency or antagonist co-contraction between groups. Thus the primary constraint on balance recovery in these children is insufficient levels of contraction of agonist postural muscles.

Developmental changes in the kinematics and kinetics underlying balance control were studied in 61 children, 9 months to 10 years of age. The children were classified according to developmental milestones as standers; new, intermediate, and advanced walkers; runners-jumpers; hoppers; gallopers; and skippers. The children experienced support-surface translations of varying size and speed. Children with greater locomotor experience withstood larger balance threats without collapsing or stepping. Analyses of scaled trials (perturbations normalized in size to foot length and center of gravity height) revealed that improvement in balance was not related to initial configuration parameters surrounding the task (degree of crouch or lean). Children with advanced locomotor skills had faster recovery times and relatively larger muscle torques than children with less experience. Relative torque-time histories of the more experienced children began to match the adult response to similar perturbations. With increased experience and changing muscle torque regulatory abilities, balance skills became more robust.

The authors investigated the emergence of independent control of body segments in bimanual tasks involving either voluntary or involuntary trunk motion by tracking the transition from an ego- to an exocentric mode of postural control during childhood (i.e., from body-referenced orientation to externally referenced action). A paradigm combining a seated manual task and various trunk manipulations described the coordination strategies used by 24 children at different ages (2 to 9 years) and by adults. The following questions were asked: (a) When do children begin to dissociate upper limb movements from those of the trunk? (b) What segmental strategies are exhibited by each age group (2-3, 4-6, and 7-9 years, and adults)? Kinematic analyses revealed that younger children (2-6 years) used either the trunk or the support surface as reference to orient the limbs. Older children (7-9 years) began to use a gravitational reference frame similar to that of adults; they uncoupled upper limb motion from the trunk in either voluntary or imposed conditions. Young children patterned the forearm trajectory after the initiating segment (support surface or the trunk), thus reducing the degrees of freedom during the dual task. Echoing previous reports, 7-9 years of age appears to be a critical period in which children master postural control and develop an internal representation of body scheme.