DEVELOPMENT OF PREHENSION MOVEMENTS IN CHILDREN - A KINEMATIC STUDY

To evaluate the normal development of functional hand motor skill, the kinematics of prehension movements were analyzed in 54 healthy childr en (age 4-12 years). The subjects repeatedly reached out for cylindric al target objects and grasped them with a precision grip Of their domi nant hand. The trajectory of the reaching hand and the finger aperture were monitored by optoelectronic motion analysis. To obtain comparabl e conditions for the different age groups, the experimental setup was scaled according to the individual body proportions of each subject. W ithin the investigated age range, neither the movement duration nor th e normalized (according to body proportions) peak spatial velocity of the reaching hand changed significantly. However, the hand trajectory straightened and the coordination between hand transport and grip form ation improved, resulting in smooth and stereotyped kinematic profiles at the age of 12 years. The younger children opened their grip relati vely wider than the older ones, thus grasping with a higher safety mar gin. The dependence on visual control of the movement declined during motor development. Only the oldest children were able to scale the gri p aperture adequately, according to various sizes of the target object s, when visual control of the movement was lacking. The results sugges t that the development of prehensile skills during childhood lasts unt il the end of the first decade of life. This functional maturation is discussed in relation to the development of neuronal pathways.