Examination of the effect of tool mass and work postures on perceived exertion for a screw driving task

Eighteen subjects with industrial work experience drove screws into perforated sheet metal at three vertical (64, 114 and 165 cm) locations with a pistol-shaped tool, and at two horizontal (13 and 63 cm) work locations using an in-line tool. Both air-powered tools were varied in mass (1, 2 and 3 kg). Subjects drove screws using each tool mass at all work locations. After driving 25 screws at a particular work location/tool mass combination, subjects assessed their perceived exertion for that condition using the Borg ten-point ratio rating scale and completed a body part discomfort survey. Both tool mass and work location were significant factors in determining the ratings. As tool mass increased, so did the ratings of perceived exertion (18% to 100%). The lowest ratings of perceived exertion were at 114 cm on the vertical surface and at 13 cm on the horizontal surface. For the vertical surface, the body part discomfort data revealed that the low back and the right arm were often cited as uncomfortable at 64 cm, the right arm was identified as uncomfortable at 114 cm, and the right arm and the chest were cited as uncomfortable at 165 cm. For the horizontal surface, at both 13 cm and 63 cm, the neck and the right arm were identified as uncomfortable. Relevance to industry This laboratory study simulated industrial work environments and subjects with industrial work experience were used. The guidelines developed through this and other related studies can be readily applied to the design of work stations or the selection of powered hand tools with the goal of minimizing the prevalence of work-related musculoskeletal disorders. It may be possible to generalize these results to other types of hand tools and workstations.