Ergonomic evaluation of screwdriver handles under different working conditions

Maximum torque strength, muscle strain and subjective responses were evaluated in a series of screwdriver tests with 10 varied handles, performed under different working conditions. Screwing in and unscrewing tasks that affected inward and outward rotations of the upper extremity muscles were measured. Maximum torque strength for supination and pronation was determined under the conditions of dry hands, using industrial gloves, and with oily hands, consecutively. Physiological cost of performance was simultaneously determined by measuring electromyographic activities (EA) of 5 muscles of the hand-arm-shoulder system that were expected to be involved in screwing tasks. Subjective assessments were made through a questionnaire before and after each experiment. Significant differences were determined between maximum torque values produced during inward and outward rotations for the three operational cases. Maximum torque values exerted by the twelve subjects using industrial gloves were substantially higher than the values obtained by dry and oily hands during both supination and pronation. EA values of the 5 muscles investigated differed significantly. However the subjective assessments of the handles did not vary in the pre and post assessments.