A pilot laboratory study of EMG back activity among normal versus overweight workers during material handling on multi-level racks
Workspace design determines the safety of a business establishment; it influences employee welfare. The issue is more pressing in the manufacturing industry, where workers often stress their bodies for long periods. They remain in standing positions, assume awkward postures, and perform repetitive tasks for extended periods. Any improvement of the design and organization of the workspace reduces the Risk for musculoskeletal injuries, particularly of the back. This research project investigated how manual material tasks in the workplace affect individuals who are overweight, and those who are not. Specifically, this research targeted stress to the back. The researcher used Electromyographic measurement techniques to measure muscle activity on four back muscles: the trapezius p. descendenz, the deltoideus p. scapularis, the infraspinatus, and the latissimus dorsi. Thirty male workers were evaluated: 15 men with a BMI less than 25 and 15 men with a BMI equal to or greater than 25. The men were evaluated in a laboratory setting using a multi-level rack that simulated actual working conditions at a manufacturing plant. The thirty participants performed material handling tasks using an electrical motor, which weighed approximately 25 lbs on the racking system. Each worker performed two sets of material handling sequences on the multi-level rack: low frequency (from ankle height to the shoulders and return to the ankles), and high frequency (from ankle height to midsection to shoulders and return to the ankles). The low and high frequency handling tasks were performed in different postures of 0, 30, and 60 degrees rotations to the mid-saggital plane. Each sequence took approximately 1 hour to complete for each worker.
The ANOVA results showed a statistically significant (p < 0.05) difference on the left and right sides of the body, the degree of rotation (0, 30 and 60 degrees), BMI level (normal weight versus overweight), and tasks (high versus low frequency) on the targeted muscles. The latissimus dorsi revealed an insignificant impact on BMI. In terms of the low and high frequency tasks, there was a significant difference between the left side for low and high frequency handling tasks. Generally, workers with lower BMI levels had higher EMG values. This laboratory study showed that there is a difference in a worker's variability and posture on the four groups of muscles evaluated. Employers could use this study to design better workspaces that will not place workers at a high risk for back injury.
0546: Industrial engineering