[Analysis of grip force during object manipulation. Method for the objective measurement of physiological normal and impaired hand function].

The control of prehensile finger forces is an essential feature of all skilled manual performance. The basic aspects of healthy grip force control have been well documented within the past two decades. In healthy subjects, grip force is accurately adjusted to the mechanical object properties such as weight, surface friction, and shape: when we move a hand-held object, grip force is modulated in parallel with movement-induced load fluctuations without an apparent temporal delay. At all phases of the movement, grip force is always slightly higher than the minimum necessary to prevent the object from slipping. The absence of a temporal delay between grip and load force profiles implies that the central nervous system is able to predict load variations precisely before the intended manipulation, and consequently regulates grip force in anticipation. Feedback from the grasping fingertips is used to adjust the force level efficiently to the actual load requirements. Pathologic grip force control affects the efficiency of the forces produced and the predictive temporal coupling between grip and load force profiles. Here we demonstrate pathologic grip force control in various neurologic disorders. The analysis of grip force control is simple and highly sensitive for detecting healthy and pathologic motor behaviour. The examination of grip force control is well suited for an objective evaluation of therapy during sensorimotor rehabilitation of deficient hand function.