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Physical Fatigue in High and Very High Frequency Manual Materials Handling: Perceived Exertion and Physiological Indicators

This paper presents the results of a preliminary laboratory study undertaken to determine the perceived exertion and physiological responses of highly trained and experienced workers to high (up to 16 repetitions/min) and very high frequency (above 16 repetitions/min) manual lifting, lowering, and carrying/turning tasks. The results indicate that workers engaged in such highly repetitive and physically demanding tasks may operate at psychophysical workloads that may clearly be considered physically fatiguing and unacceptable according to the current physiological design criteria. In this study subjects performing lifting and lowering tasks, on the average, operated at 57% and 52% of their uphill treadmill aerobic capacity, respectively. For carrying and turning tasks, the average metabolic energy expenditure rate corresponded to 43% of subjects' aerobic capacity. The overall heart rates of the study subjects were 155 beats per minute (bpm) for lifting, 144 bpm for lowering, and 142 bpm for carrying and turning. These physiological responses, when compared with recommended physiological design criteria, are excessively high. The ratings of perceived exertion (RPE) for the shoulder, back, and whole body were highest for lifting (range, 10.20-15.50) and least for carrying and turning (range, 10.30-13.40; carrying and turning activities also included RPE of arms). Generally workers perceived the associated physical exertions as acceptable.