Developmental changes in prehension during childhood

Recent evidence has shown that the anticipatory control of grip and load force is not innate and develops over several years in childhood. The present study examined the development of grasping behavior by quantifying the relationship between grip force and the vertical acceleration of an object. Children and adults were requested to use a precision grip to lift an instrumented object which varied in size and weight. Grip force, grip force rate and the vertical position and acceleration profiles of the test object were measured or calculated. The results demonstrated the presence of distinct developmental milestones in the maturation of precision grip from 2 to 9 years of age. With 2-year-old children, the peak acceleration was negatively correlated (r=-0.51, n=34, P<0.01) with peak grip force during lifting. By 3 years of age, peak acceleration and peak grip force during lifting became positively correlated (r=0.28, n=104, P<0.01) and the correlation continued to strengthen up to 9 years of age. Variations in the temporal coupling of both peak grip force and peak acceleration also decreased with maturation. Furthermore, starting at 4-years-old, children clearly controlled the acceleration and deceleration of the object in a symmetrical pattern and used a single burst of grip force rate to grasp the object with some regularity, suggesting that the emergence of an anticipatory control strategy had already begun.