Effects of worker anthropometry and workplace design upon shoulder discomfort and task productivity
Enhancing our understanding of the relation that exists between productivity and musculoskeletal disorders is essential to the successful design of person-machine systems for safe and comfortable human use. This research comprises two experiments to study the trade-offs between productivity and shoulder musculoskeletal discomfort in a repetitive task performed at different repetition rates. The objective of the first experiment was to determine from velocity profiles which theoretical movement time model adequately predicted the times for a mail sorting task. Based on the percentage of the total variance explained by the regression models, it was concluded that the optimized initial impulse model (Meyer et al., 1988) using one sub-movement provided the best prediction for the movement times associated with the repetitive task. In addition, the effects of different duty cycles upon movement time were studied. It was found that a decrease in repetition rate produced an increase in mean movement time.
In the second experiment a regression model that related biodemographic, anthropometric, workplace and kinematic factors to shoulder musculoskeletal discomfort was developed. Also, the effects of these ergonomic factors upon shoulder musculoskeletal discomfort were studied. It was found that the kinematic variables played the most important role in increasing the percentage of the total variance explained by the regression model. Results showed a significant linear relationship between weight and shoulder musculoskeletal discomfort. High weight values were associated with higher discomfort scores. To diminish the discomfort values it was recommended the improvement of the worker-machine system by designing adjustable equipment within the capabilities of the people to optimize their performance at work.
The associations between (1) the number of repetitions, (2) movement time and (3) shoulder musculoskeletal discomfort were studied. It was determined that, if the anthropometry of the working population is considered, an adjustment point for the movement time could be identified (which determines the productivity level of the workers) and a better design of a repetitive task could be achieved. Finally regarding the discomfort-productivity trade-off evaluation, it was found that higher SMD scores were associated with longer movement time values regardless of the experimental population percentile.
0354: Occupational safety