PSYCHOPHYSICAL STUDIES OF REPETITIVE WRIST FLEXION AND EXTENSION

The purpose of this experiment was to investigate the feasibility of u sing psychophysical methods to determine maximum acceptable forces for various types and frequencies of repetitive wrist motion. Four adjust able work stations were built to simulate repetitive wrist flexion wit h a power grip, wrist flexion with a pinch grip, and wrist extension w ith a power grip. The study consisted of two separate experiments. Sub jects worked for two days per week during the first experiment, and fi ve days per week during the second experiment. Fifteen women completed the first experiment, working seven hours each day, two days per week , for 20 days. Repetition rates of 2, 5, 10, 15 and 20 motions per min ute were used with each flexion and extension task. Maximum acceptable torques were determined for the various motions, grips, and repetitio n rates without dramatic changes in wrist strength, tactile sensitivit y, or number of symptoms. Fourteen different women completed the secon d experiment, performing a wrist flexion motion (power grip) fifteen t imes per minute, seven hours per day, five days per week, for 23 days. There were no significant differences in maximum acceptable torque fr om day to day. However, the average maximum acceptable torque for a fi ve days per week exposure was 36.3% lower than for the same task perfo rmed two days per week. Assuming that maximum acceptable torques decre ase 36.3% for other repetition rates and motions, tables of maximum ac ceptable force were developed for female wrist flexion (power grip), f emale wrist flexion (pinch grip), and female wrist extension (power gr ip).