Maximal Acceptable Torques of Six Highly Repetitive Hand-Wrist Motions for Male Industrial Workers

Abstract

Objective: The purpose of the study was to quantify maximum acceptable torques (MATs) in 16 healthy male industrial workers while performing six motions: 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). Background: Psychophysical studies on repetitive motions of the wrist and hand were previously reported on women; however, it is not clear how men will psychophysically respond to similar motions. Method: A psychophysical methodology was used in which the participant adjusted the resistance on the handle. Repetition rates for these tasks were 15 and 25 per minute. Participants performed the tasks for 7 hours per day, 5 days per week, and for 12 days. Symptoms were recorded by the subjects at the end of each hour. Results: The mean MATs 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. The higher the repetition rate, the lower the MAT. Depending on the type of task and repetition rate, these values represented 15% to 35% (median of 23%) of their maximum isometric torque. Application: Based on aforementioned findings, a table of MATs and derived acceptable forces for six tasks at different percentage capabilities of the male industrial populations is formulated.