Power hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders (UEMSDs). The reaction forces affect the subjective ratings of perceived exertions associated with tool operations. This paper addresses how operators perceived power nutrunner torque reactions. Two work configurations using pistol grip and right angle tools were tested in the laboratory. Twenty male participants operated four automatic shutoff pneumatic nutrunners on two different task joints using various postures. Handle displacement and the grip force for each torque reaction was monitored. Subjective ratings of discomfort and acceptance toward the given reaction were recorded. The results show that discomfort and acceptance for torque reactions were significantly affected by grip force but not by handle displacement. Odds ratios using grip force as a predictor were calculated. This study can helping setting physical exposure limits encountered in power nutrunner operations.
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