PERCEIVED EXERTION AND DISCOMFORT ASSOCIATED WITH DRIVING SCREWS AT VARIOUS WORK LOCATIONS AND AT DIFFERENT WORK FREQUENCIES

Eighteen subjects drove screws with air-powered tools into perforated sheet metal at three vertical and two horizontal work locations using three different work paces (8, 10, and 12 screws/min). Subjects drove screws with a pistol-shaped tool on the vertical orientation at knee, elbow, and shoulder height. They used an in-line tool to drive screws on the horizontal surface. A horizontal beam was placed just below eac h subject's elbow height and they drove screws into it with the lower arm perpendicular to the torso and with the arms fully extended. Subje cts drove screws for 10 min at each work location and frequency combin ation before they assessed the condition using the Borg ten-point rati o rating scale. Subjects also ranked seven body areas according to dis comfort for each work location. A two-factor ANOVA (and comparable non -parametric statistics) showed that both work location and frequency w ere significant factors in determining the Borg ratings. As work pace increased, so did the Borg ratings of perceived exertion for each work location. For each incremental increase in work pace, the Borg rating s of perceived exertion increased 12% to 25%, depending on the work lo cation. Driving screws at elbow height on the vertical surface and wit h the lower arm close to the body on the horizontal surface were the w ork locations with the smallest ratings of perceived exertion. The rat ings of perceived exertion for driving screws at elbow height on the v ertical surface were 18% to 50% lower than the ratings for driving scr ews at knee or shoulder height and the ratings of perceived exertion f or driving screws with the lower arm close to the body on the horizont al surface were 21% to 24% lower than driving screws with the arms ful ly extended. No significant difference was found among the discomfort ranks given to the various body parts for the two horizontal work loca tions. Differences were found among the body part discomfort rankings for the vertical work locations. While driving screws at knee height, the torso was most stressed; the wrist and hand were most stressed whi le driving screws at elbow height, and the shoulder and upper arm were the body parts that were stressed the most while driving screws at sh oulder height.