Closure and firm grasp result from the strong action of the extrinsic flexors and the intrinsics of both the thumb and fingers. Finally, slight extension of the wrist tightens the grip even more. The great variability in the postures of grasp would seem to exclude easy classification. Power grip is thought to have developed early in humans and consists of a prehensile movement in which the object is grasped by the fingers and pressed against the buttress of the thumb and its intrinsic muscles. This is a powerful movement with little skill involved.
Precision grip is thought to be the most recent adaptation of the evolving human hand.
It is an accurate prehensile action in which the object may be held away from the palm between thumb and fingertips. The so-called hook grip, while of great use to the apes suspended in trees, is only of use in humans when carrying suitcases. Formerly 3 clinical models could be used for the study of grasp. Nowadays, with the conquest of poliomyelitis, only the rheumatoid hand and the leprosy hand are available. Practically every biomechanical imbalance that afflicts the hand occurs in one or the other of these 2 diseases.