Anticipatory Control of Grip Force in Rapid Arm Movement

The force used in grasping an object in a precision grip orthogonal to the line of motion is unaffected by the arm movement and so offers a direct window on the nervous system's plans for arm motion.

Abstract

The functional significance of the grip force is that it allows the development of a frictional force that opposes the load force. The grip force that people use when holding an object in the air is generally only slightly greater than the minimum required for a given surface to prevent slip. It thus makes sense to speak of a safety margin, which may be defined as the ratio of the excess grip force to the minimum grip force that just prevents slipping. The mass of the object determines the load force and, in combination with the frictional conditions, the minimum grip force required to keep the grip force/load force ratio above the slip ratio in static holding. With stabilization of the object in the hand the geometric relations between hand and object are preserved. In voluntary arm movements there are important parallels between anticipatory modulation of grip and anticipatory postural adjustments. The force used in grasping an object in a precision grip orthogonal to the line of motion is unaffected by the arm movement and so offers a direct window on the nervous system's plans for arm motion.