Investigating Differences of the Movement Variability and Movement Smoothness in Reaching and Grasping Task in Children and Adults

Reaching and grasping is one of the most basic fundamental skills. The aim of this study was to address the differences of movement variability and movement smoothness in reaching and grasping in children and adults. 60 children (age range: 8-13 years old) were divided into 6 groups. The task used in the study included reaching and grasping a cube with the dimension of 3.6 cm
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which provided the palmar grasp for all children. Subjects had to grasp the cube with their dominant hands and brought it near their mouth. In addition, a group of adults participated in this study (age range: 24+1.2). Participants performed 10 trials and kinematic variables including mean squared jerk, dimensionless jerk, range of motion of elbow joint, and variability in coordination pattern were calculated. One-way ANOVA was used to analyze the data in each variable. The results showed that the 13-year-old group was significantly different than adult group in the mean squared jerk and dimensionless jerk. It was observed that 8- and 9-year-old groups had significant differences with other groups in range of motion of elbow joint and variability in coordination pattern; however, there was no differences among other groups. Overall, the results showed that the growth process of reaching and grasping is not limited to the early childhood. These results were interpreted according to the development of motor control and asynchronous acquisition of kinematic variables in the process of movement skill learning.