Analysis of grip and pinch strength using inverse dynamics simulation technique

Grip strength is the function of musculotendinous action across the finger joints and varies while dealing objects of varying size and shape. Increasing object size requires greater effort by the fingers to grip. The main objective of this study is to analyse the variation in grip and pinch strength exerted on objects of various sizes and shapes in a short span of time. OpenSim 3.3 is open-source musculoskeletal modelling software used for performing simulations in a dynamic environment. The generic wrist model in OpenSim has movements on index finger and thumb only, for study purpose. Objects of various sizes were designed and imported in OpenSim. This study determines the joint moments exerted by the fingers during grip activities. Original model was modified and custom joints were placed in the proximal and distal phalanx joints of the fingers. This allowed the finger segments to undergo translational and rotational movements. Coordinates of the custom joints were adjusted to provide constraints in the joint movement to hold the objects in position. For grip strength, objects of various sizes and shapes were imported to OpenSim. Simulation was carried out for gripping the objects for a specified time period. The force generated by the synergistic movements of finger segments was compared among grip and pinch of different objects. This method is used to determine the grip and pinch strength by handling objects of different shapes and sizes under the influence of time.