Maximum acceptable forces for repetitive wrist extension with a pinch grip

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to quantify max imum acceptable forces for extension motions of the wrist performed with a pinch grip. Subjects grasped a handle with a pinch grip and moved it throug h a 1.57 rad (90 degrees) extension wrist motion (similar to a light assemb ly operation). A psychophysical methodology was used in which the subject a djusted the resistance on the handle, and the experimenter manipulated or c ontrolled all other variables. Twenty subjects performed the task at repeti tion rates of 15, 20 and 25 motions per minute. Subjects performed for 7 h per day, 5 days per week, for 4 weeks. 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 m in of each hour. The results are presented and compared with maximum accept able forces for other types of wrist motion investigated in previous studie s. Maximum acceptable force for wrist extension with a pinch grip is smalle r than any of the other motions investigated so far. Relevance to industry Cumulative trauma disorders of the upper extremities continue to be a probl em for industrial workers who perform repetitive tasks. Although a number o f physical risk factors have been identified, there are very few data avail able for establishing acceptable levels of these risk factors. This study a ttempted to collect such data. (C) 1999 Elsevier Science B.V. All rights re served.