Effect of tool shape and work location on perceived exertion for work on horizontal surfaces.

Thirty subjects drove screws into perforated sheet metal mounted on a horizontal surface using three air-powered tools that varied in shape (right-angle, in-line, and pistol-shaped). The four horizontal work locations ranged from 13-88 cm in front of the body and were placed at 25 cm intervals. The vertical placement of the horizontal beam was at midthigh, elbow, and midchest height. Subjects drove 25 screws at each tool/work location combination before rating that condition using the Borg 10-point ratio rating scale. The ratings of perceived exertion increased with increasing horizontal distance from the body. When tool shape was not considered, the perceived exertion was virtually equal for driving screws at midthigh or elbow height. The ratings at midchest height were significantly higher than elbow and midthigh height. When tool shape was taken into account, subjects perceived less exertion driving screws with the pistol-shaped tool at midthigh height. The in-line and right-angle tools had the lowest ratings of perceived exertion for driving screws at elbow and midchest height.