Differences in postural control and movement performance during goal directed reaching in children with developmental coordination disorder.

Poor upper-limb coordination is a common difficulty for children with developmental coordination disorder (DCD). One hypothesis is that deviant muscle timing in proximal muscle groups results in poor postural and movement control. The relationship between muscle timing, arm motion and children's upper-limb coordination deficits has not previously been studied. The aim of this study was to investigate the relationship between functional difficulties with upper-limb motor skills and neuromuscular components of postural stability and coordination. Sixty-four children aged 8-10 years, 32 with DCD and 32 without DCD, participated in the study. The study investigated timing of muscle activity and resultant arm movement during a rapid, voluntary, goal-directed arm movement. Results showed that compared to children without DCD, children with DCD took significantly longer to respond to visual signals and longer to complete the goal-directed movement. Children with DCD also demonstrated altered activity in postural muscles. In particular, shoulder muscles, except for serratus anterior, and posterior trunk muscles demonstrated early activation. Further, anterior trunk muscles demonstrated delayed activation. In children with DCD, anticipatory function was not present in three of the four anterior trunk muscles. These differences support the hypothesis that in children with DCD, altered postural muscle activity may contribute to poor proximal stability and consequently poor arm movement control when performing goal-directed movement. These results have educational and functional implications for children at school and during activities of daily living and leisure activities and for clinicians assessing and treating children with DCD. Copyright 2002 Elsevier Science B.V.