With the invention of strain gauges, isometric finger forces such as those produced during grasping an object could be measured continuously, precisely and without major constraints to the grip. In the precision grip between thumb and index finger, elementary performance aspects such as maximum grip force, ability to maintain a constant force, fast force changes or tracking of a dynamic target have been studied. In 1984, Johansson and Westling presented their paradigm based on the measurement of grip and load forces during grasping and lifting of an object. Their studies inspired a great deal of scientific interest in this aspect of fine motor control examined in healthy subjects as well as in patients with peripheral or central nervous system diseases. Research in this field progressed by introducing other motor tasks with specific demands on the control system, such as the compensation of inertial forces during movements of grasped objects. In addition, methods improved by technical developments such as 6-degree-of-freedom force/torque sensors, autonomous measurement devices, or force matrices to measure pressure distributions at grasping surfaces. Thus, measurements of isometric grip forces during object manipulation became a widely used method in neurophysiological and clinical motor sciences.
Control of isometric grip forces
Historically, the typical way to measure the force generated by the fingers or the whole hand was via compression of springs (e.g. Du Mensil de Rochemont, 1926). In addition, objects with known weights were used to load the hand or the fingers with a defined force (Truschel, 1913).