The prehensile ability with fingers has long been recognized as one of the most significant evolutionary development to human and some of the non-human primates. At birth neonates demonstate a reflex grasping to tactile stimulation of the plan, but it disappears before few months of age. From this time, the infants start to voluntarily grasp an object, and by the age of 10 to 12 months, individual fingers are involved in the grasping actions. This study is concetned with development of the capacity to generate coordinated isometric force actions which are used for a successful lifting of a small object with precision grip. A total of 93 children aged from 19 months to 13 years and 15 adults served as subjects for the study. The experimental set-up consisted of an instrumented lifting object (wt.=200 grams), a photoelectric position detector,and an IBM personal computer data acquisition and analysis system. Grip force and load force (the vertical lift force) acting on the object, and the vertical displacement of the object were recorded. The subjects were instructed to make a sequence of reaching, gripping and lifting actions for the object in an ordinary manner five times after some practice trials. Both temporal and force parameters describing critical events of the time-history curves of the grip and load forces and position were selected for subsequent evaluation. It was found that younger children aged below 5 years compared to adults were significantly slow in sequencing the task, and their grip forces were higher. A higher trial to trial variability was also noted in force parameters for these young children than adults. A general trend in development of controlling the timing and force application during grip-lift actions showed that there was a rapid progress of the capacity between 1 and 4 years of age, and a moderate progress between 5 and 8 years. The trial to trial variability data indicated that there was some refinement of the capacity between 9 and 13 years.These results demonstrated that to have a well developed prehensile capacity as seen in adults, it required a relatively long period of time during childhood. Poor capacity in young children was believed to be related to an immature state of the function of corticospinal descending pathway,of inhibitory input to the motor neuron pool activating the fingers, and of the central nervous system which allowed a feedforward stretegy of motor actions.
