Psychophysical study of six hand movements

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to qua ntify maximum acceptable forces of six motions performed on separate days b ut within the context of the same experiment. The six motions were wrist fl exion with a power grip, wrist extension with a power grip, wrist flexion w ith a pinch grip, wrist extension with a pinch grip, ulnar deviation with a power grip, and a handgrip task (with a power grip). A psychophysical meth odology was used in which the subject adjusted the resistance on the handle and the experimenter manipulated or controlled all other variables. Thirty -one subjects performed the six tasks at repetition rates of 15, 20 and 25 motions/min. Subjects performed the tasks for 7 h per day, 5 days per week, for 4 weeks. The subjects were instructed to work as if they were on an in centive basis, getting paid for the amount of work performed. Symptoms were recorded by the subjects during the last 5 min of each hour. The results r evealed that maximum acceptable torques ranged from 11 to 19% of maximum is ometric torque depending on frequency and motion. Maximum acceptable torque s for the tasks that could be compared with previous studies showed the sam e patterns of response. However, the selected forces were substantially low er using the mixed protocol. A table of maximum acceptable torques and forc es is presented for application in the field.