Utility of using a force and moment wrench to describe hand demand

Abstract

This study was undertaken to evaluate the utility of using a force and moment wrench to describe the demand on the distal arm tissues and perceived exertion during static gripping tasks. Five right hand dominant university students, who were free of hand or wrist disorders, completed a total of 87 maximum and submaximum gripping tasks. All trials were completed while standing, with the arm adducted and elbow flexed to ninety degrees. The wrist posture was near neutral in all axes during the exertions. Activation levels for muscles of the forearm and hand and rating of perceived exertion were collected. Participants handled objects using 3 grips (cylindrical grip, lateral pinch and pulp pinch) in 8 different ways. The equivalent force and moment wrench for the tasks were also exerted on a modified pinch/grip dynamometer, affixed to a six degree of freedom force cube. This instrumentation allowed the simultaneous collection of the 3 forces, 3 moments and the pinch/grip force about the grip centre. It was expected that the demands of a task and the instrumented task wrench reproduction would be the same, and therefore the slope of the linear regression for the EMG and RPE scatterplots would be equal to one. The RPE slopes ranged from 0.99 (lateral pinch) to 1.11 (cylindrical grip), with R2 greater than 0.89 for all grips. The mean slope for EMG of all muscles ranged from 0.89 (lateral pinch) to 1.38 (pulp pinch), with mean R2 of 0.61 to 0.68. The force and moment wrench system for the categorization of prehension appears to capture the demands on the distal arm tissues and perceived exertion during standardized laboratory holding tasks.