Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Final Grant Report R01-OH-01429, 1984 Aug; :1-153
The principal objectives of this research project were to generate the maximum acceptable weight of lift data for extended workshifts (twelve hours per day) for the industrial population and to develop models for predicting lifting capability of individual workers as a function of operator variables, task variables, and shift duration. Thirty-seven male and thirty-seven female workers, recruited from industries located in the Greater Cincinnati area, participated in the study. Subjects performed thirty-six different variations of manual lifting task in a controlled laboratory setting. Using the psychophysical methodology, workers determined the maximum weight acceptable to them for 8- and 12-hour lifting durations. During the experiment, their heart rate and oxygen uptake were continuously monitored. A subset of the sample population, five males and five females, also participated in the study conducted to verify the psychophysical approach in manual lifting and to determine changes in metabolic energy expenditure rate and heart rate with the lifting duration. The results of statistical analysis performed on the experimental data indicated that: 1. the psychophysical methodology overestimates lifting capability of individuals by as much as 30%. 2. the physiological fatigue criterion of 5 kcal/minute results in metabolic overloading for 8-hours of work. 3. for 8-hour shifts, males selected weights that, on the average, resulted in metabolic energy expenditure rates of 29% of their aerobic capacity; females required metabolic energy expenditure rates equivalent to 28% of their aerobic capacity. 4. for 12-hour shifts, males selected weights that on the average, resulted in metabolic energy expenditure rates of 23% of their aerobic capacity; females required metabolic energy expenditure rates equivalent to 24% of their aerobic capacity. 5. the average heart rate at the maximum weight acceptable for 8-hour shifts were 99 and 104 beats per minute (bpm) for males and females, respectively. For 12-hour shifts, the average heart rate of males and females at the maximum acceptable weight of lift were 90 and 101 bpm, respectively. 6. the data generated in this study compare very well with those reported in the literature. The effects of task variables (frequency, box-size, lifting height) were also very similar. Lifting capability data bases, for the 12-hour shifts, are reported as a function of lifting frequency, box-size, and height of lift. Data collected in previous studies on industrial workers, for 8-hour shifts, were integrated with those generated in this study to develop comprehensive maximum acceptable weight of lift database for regular 8-hour work shifts. Lifting capability prediction models, which take into con-sideration worker profile, task descriptors, and shift duration, are provided. Also provided are models to predict heart rate and oxygen uptake at the maximum acceptable weight of lift.