Maximal Acceptable Torques of Highly Repetitive Screw Driving, Wrist Flexion and Extension with a Pinch grip, Ulnar Deviation, and Handgrip Tasks for Seven Hour Workdays for Male Industrial Workers

Abstract

The purpose of the study was to quantify maximum acceptable torques of six tasks performed on separate days but within the context of the same experiment. The six tasks were screw driving clockwise with a 40 mm handle and a 39 mm yoke handle; flexion and extension with a pinch grip; ulnar deviation with a power grip (similar to knife cutting), and a handgrip task (similar to a pliers task). A psychophysical methodology was used in which the subject adjusted the resistance of the task, and the experimenter controlled all other variables. Sixteen male industrial workers performed the six tasks at repetition rates of 15 and 25 motions per minute. Subjects performed the tasks for 7 hours per day, 5 days per week, for 12 days. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work they performed. Symptoms were recorded by the subjects during the last 5 minutes of each hour. The results revealed that mean maximum acceptable torques ranged from 1.15 Nm to 1.88 Nm for screw driving, 2.26 Nm to 3.71 Nm for pinch flexion and extension, 3.88 Nm to 4.07 Nm for ulnar deviation, and 11.47 Nm to 13.98 Nm for the handgrip task. These values represented 15% to 35% (median of 23%) of maximum isometric torques depending on the repetition rate and the task.