AN ELECTROMYOGRAPHIC STUDY OF MAXIMUM TORQUES AND UPPER EXTREMITY MUSCLE-ACTIVITY IN SIMULATED SCREWDRIVING TASKS

The effects of workstation and tool handle design on strength and uppe r extremity muscle activity during a simulated manual screwdriving tas k were examined. Fifteen male participants performed maximal (100%) an d submaximal (75% and 50%) exertions with a screwdriver using postures frequently observed in industry. Investigators varied handle height, reach distance, handle diameter, and handle orientation during the exp eriment. The activity of the anterior deltoid, triceps brachii, biceps , extensor digitorum, flexor digitorum superficialis and flexor pollic is long-us was monitored using surface electromyography (EMG). The rat io of normalized EMG activity to torque produced during the exertion w as computed for each muscle under each condition. The results indicate d that increased torque capability was associated with the use of a la rger (3.7 cm), vertically oriented handle, EMG/torque ratio generally increased as handle height was increased, reach distance and handle di ameter were reduced, and the handle orientation was changed from verti cal to horizontal. This study supports the premise that workstations a nd tools can be configured to maximize worker capabilities while minim izing the potential for muscle strain and fatigue. These data may be u seful to job analysts for assessing the relative demands of constructi on and assembly work. (C) 1997 Elsevier Science B.V.