Effect of task constraint on reaching performance in children with spastic diplegic cerebral palsy

The purposes of the study were to examine the effect of task constraint on the reaching performance in children with spastic cerebral palsy (CP) and to examine the correlations between the reaching performance and postural control. Eight children with CP and 16 typically developing (TD) children participated in the study. They performed a reach-and-return task with a seated posture on a stool. The target for reaching was set at a 120% arm-length distance in three directions (anterior, medial, and lateral). Reaching speed was modulated with a metronome at a rate of 46 beats/min. A motion analysis system recorded the kinematic data of reaching at a sampling rate of 150 Hz. Postural control was assessed with a pediatric reaching test. Movement time (MT), straightness ratio (SR), hand peak velocity (PV), and movement unit (MU) of reaching were compared between groups and among task conditions with repeated measure ANOVAs. Pearson's product-moment correlation coefficients were used to examine the correlations between reaching and postural control. Children with CP presented longer MT, larger SR and more MU than did TD children. Further, the children with CP showed larger SR while reaching medially and laterally than anteriorly. But TD children were not affected by these task constraints. Moderate correlations between postural control ability and SR and MU were noted. In conclusion, the children with CP showed a slower, more skewed, less efficient and less coordinated pattern of reaching than the TD children. Reaching laterally and medially seemed to impair the reaching performance (more skewed and less efficient) of the children with CP, but not of the TD children. Reaching laterally and medially may involve trunk rotation which produces more postural challenges than reaching anteriorly. This finding may explain the difference in the effect of task constraint on hand reaching performance between the two groups of children. Moreover, the better the postural control ability, the straighter, and more efficient and coordinated reaching performance the children showed.