Effect of a Manual Screwdriver with a Pistol-Grip Handle on Maximum Torque and Muscle Activity

Abstract

Electric utility power plant electricians use a conventional manual screwdriver to loosen and tighten small fasteners on a day-to-day basis, which may expose them to risk of musculoskeletal disorders (MSDs) affecting the wrist and upper extremity. Using a screwdriver handle that requires less muscle activity to exert the same level of torque can reduce the risk of MSDs. Maximal forearm torque in both supinating and pronating directions and at 3 forearm positions (supinated, neutral and pronated) were tested with 2 screwdrivers, a conventional straight-handled tool and pistol-grip screwdriver. Electromyography (EMG) of the finger flexor and extensor muscles and the biceps were monitored while performing maximal forearm torque exertions in the pronating and supinating directions at 3 forearm positions. The torque exerted while using the pistol-grip screwdriver was twice as great as with the straight handle (8.47 and 4.24 Nm, respectively). The turning direction affected maximal torque and interacted with position of the forearm. Normalizing maximal torque data to the muscle activity (Nm / %MVC EMG) revealed that the pistol-grip tool was much more efficient than the straight handle tool.