The coordination of multi-joint reaching movements: A developmental profile
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The study of visually-guided reaching has been a meaningful tool to investigate sensory-motor coordination in typical development and different clinical paediatric populations. The aim of this study was to characterize the development of multi-joint reaching behaviour in children and youth, from 5 to 16 years of age, allowing us to capture changes that may occur into adolescence. Participants were 68 able-bodied children and youth, with no history of developmental, educational or social problems. A stratified recruitment strategy was used to adequately represent five age groups: I (5-6 years), II (7-8 years), III (9-10 years), IV (11-13 years) and V (14-16 years). A center-out reaching task was used as it allowed us to measure effects of limb mechanics during reaching. Different patterns of inter-segmental motions at the shoulder and elbow joints were needed to reach the different targets: flexion at both joints, extension at both joints, and a mixed-coordination pattern. Children were asked to reach quickly and accurately to 8 targets located at 45 degree intervals around the perimeter of a circle with a 6 cm radius. The development of reaching was described using non-parametric statistics. The global features of path length and total movement decreased as a function of increasing age, with less variability observed in older participants (p<0.05). This increased accuracy was explained by a significant reduction (p<0.05) in distance and direction error of the first movement component of the reach, indicative of the increasing ability of children to accurately plan movements based on an internal representation of the limb. These older children were also able to respond to the visual target more quickly (p<0.05). In general, initial direction errors and total movement time increased from a minimum for the 2-joint flexion coordination to a maximum for the mixed-coordination pattern. The magnitude of error, however, decreased as a function of age (p<0.05), and in particular for the mixed-coordination pattern (p<0.01). This center-out task is therefore considered to be responsive to observe effects of development and limb mechanics on performance. The established normative data set will provide a reference for the measures of performance in children with neurodevelopmental disorders.