Development of postural responses during standing in healthy children and children with spastic diplegia.

Studies on the development of balance control show a clear developmental progression of the emergence of organized muscle response patterns, with tonic background muscle activity decreasing and phasic bursts of activity emerging in all three agonist muscles in a synergic group (gastrocnemius-hamstrings-trunk extensors or tibialis anterior-quadriceps-abdominals) just prior to the onset of independent stance. The rudimentary ability to adapt postural responses to changing task conditions is present in children as young as 1 year of age. Older children with spastic diplegia have muscle activation patterns typically seen in normal children who are at the pull-to-stand stage of development, including poorly organized (proximal activated before distal muscles) responses with a high degree of antagonist co-activation. When normal children were asked to stand in a crouched posture like the CP children, the additional constraint caused muscle response patterns to resemble those of CP children, suggesting that differences in balance control in CP children are due to both CNS deficits and biomechanical changes in postural alignment.