A psychophysiological study of high and very high frequency manual materials handling: Part I - Lifting and lowering

Abstract

This paper describes the first part of a two-part study undertaken to determine the psychophysical and physiological responses of male workers to short duration (2 hours), high (up to 16 times per minute) and very high (above 16 times per minute) frequency manual handling tasks. Manual lifting and lowering tasks were studied in the first part of the study. The handling frequencies investigated were: 14, 16, 18, 20, and 22 per minute. Ten highly trained males participated in the study. Their metabolic energy expenditure rate, heart rate, and ratings of perceived exertion (RPE) of the shoulders, back, and whole body at the maximum acceptable weight of lift/lower were determined. How the physiological responses changed with the working duration was also investigated. The results indicated that heart rate and oxygen uptake remained steady with the working duration. Although the maximum acceptable weight declined significantly with frequency, the sample population chose a consistent work rate (approximately 145 kg-m/min, on the average). Other responses, however, were not affected significantly by frequency. Also, on the average, subjects performing manual lifting tasks operated at approximately 60% of their lifting aerobic capacity (equivalent to approximately 57% of their graded treadmill aerobic capacity). Subjects performing lowering tasks operated at 55% of their lifting aerobic capacity, on the average (equivalent to approximately 52% of their graded treadmill aerobic capacity). These findings are substantially different from those observed in previous studies for 8-hour work shifts and lower frequencies and indicate that individuals performing high and very high frequency manual lifting or lowering tasks are subjected to very high physical and physiological burden.