Upper extremity cumulative trauma disorders have been linked to the repeated and/or forceful exertions and/or awkward postures sometimes required by upper extremity intensive work. The combined effect of these physical stressors can be evaluated using psychophysical methods. The purpose of this study was to examine different combinations of repetitive upper extremity work using established psychophysical methods to determine design recommendations for upper extremity tasks. The tasks studied simulated assembly line type work where a part is transferred from a storage bin and attached with a pneumatic tool to another larger part. Twenty-four experienced industrial workers performed five combination tasks of transferring an object along a conveyor and screw driving using a pistol shaped pneumatic screwdriver: 100% transfer; 75% transfer and 25% screw drive; 50% transfer and 50% screw drive; 25% transfer and 75% screw drive; and 100% screw drive. The cycle time was 24 seconds. Each combination task was performed for an hour. Overall, transferring, and screw driving perceived exertions were measured using 10 cm visual analog scales (VAS) with verbal descriptions at the endpoints. The left and right sides corresponded to “Easiest imaginable work” at 0 cm, and “Hardest imaginable work” at 10 cm, respectively. Body part discomfort surveys were utilized to assess discomfort from each of the tasks. The overall perceived exertion (VAS) rating increased, as the task utilized more of one upper extremity than the other and involved more of either the transferring or screw driving tasks. The mean overall VAS ratings were 5.3, 4.3, 3.5, 4.4, and 5.3 for the five combination tasks, respectively. As the transferring (or screw driving) proportion of the task increased, the transferring (or screw driving) VAS increased. A repeated measures ANOVA showed that the combination task effect was significant (p<0.01). This psychophysical data can provide guidance in the analysis and design of upper extremity work. Since less varied work which utilized more of one upper extremity than the other had greater overall perceived exertion, upper extremity tasks should be designed as varied as possible utilizing as many body parts as possible. Body part discomfort surveys verified that this decreased discomfort severity and distributed the discomfort more evenly throughout the different body parts. This study provides evidence of the positive effects of work enlargement.
Quantitative Estimation of Forearm Strength and Associated Muscle Fatigue on the Screw Driving Task
