Kinematic characterization of functional reach to grasp in normal and in motor disabled children

The upper limb kinematics were assessed during the execution of a functional task in healthy adults, children and in children with motor disabilities (i.e. hemiplegic cerebral palsy (HCP) and movement disorders (MD)). The quantitative assessment was performed considering the time durations, the amplitude of movements at different joints and the periodicity of the acceleration patterns.

Compared to adults, healthy children showed increased motion amplitudes both at the head and at the trunk; this is suggestive of a reduced ability to stabilize the head during reaching. Furthermore, healthy children showed a reduced periodicity of the acceleration patterns which is interpreted as an indication of the on-going maturation process of the central nervous system.

Subjects with HCP and MD showed increased movement duration; however this general finding does not account for specific differences. Indeed, children with HCP showed reduced range of motion (ROM) of the shoulder on the frontal plane which is counterbalanced by the introduction of compensatory movements of the trunk. Conversely, in children with MD, the ROM is well-preserved whereas the movements of the head are increased especially at higher speed. Finally, the periodicity of the end-effect is dramatically reduced both in HCP and MD. This suggests the existence of out-of-phase corrective strokes that may indicate an increased variability of the motor control commands.

The results of this study reinforce the evidence that kinematic analysis may add valuable information to understand the developmental process in healthy children and to differentiate distinct levels of impairment in children with neurological disorders.