Date of Graduation
Statler College of Engineering and Mineral Resources
Industrial and Managements Systems Engineering
Past research indicates that, in general, individuals performing material handling tasks tend to underestimate lower back stress, i.e. L5/S1 disk compression, adopting free style lifting postures that often results a greater biomechanical stress in the lower back, increasing their potential risk of developing low back injuries in the short, mid and long terms.;The main objective of this research was to identify within theoretically safe workstation layouts, the subgroup of layouts that would lead workers to adopt cognitively comfortable and at the same time physically safe lifting postures. This research objective was achieved through the use of the Aesthetic Ergonomics Dual process discipline deployed in 2 interlinked stages: (1) the development, implementation and analysis of a survey where 121 experienced workers identified important cognitive factors and attributes which lead them to adopt perceived comfortable starting lifting postures in the sagittal plane, and (2) the design, implementation and analysis of a laboratory experiment where 20 workers experienced in material handling performed 12 different lifting, using a magnitude estimation scale to rate their perceived comfort at each lifting task. All lifting tasks were designed based on a lifting index, LI, which was set equal to one (1) according to the 1981 NIOSH Lifting guide.;Results of this study indicated that independent of horizontal reaches and container weights, workstations should be designed with a vertical height of approximately 30 inches. When compression and shear forces on the L5/S1 disc and subjects' average heart rate were considered in the analysis, the results support the recommendation that 30 inches should be the preferred vertical height in the design of workstations where lifting is frequently performed. The highest vertical height evaluated, 45", was associated with lifting tasks that posed a significantly higher physical demand on subjects' shoulders, depicted as an inconsistency between subjects' perceived comfort for 45" and this height's corresponding average shear and compressive forces estimates for subjects' L5/S1 disc. It was also found that average subject's perceived comfort decreased as the weight of the object lifted increased, is independent of the horizontal distance of the lift. However, the weight of the object lifted resulted in a significant increase in the subjects' estimated L5/S1 compression force with an increase in the height, which indicates that the counterpart nested factor in Zn, the horizontal distance, had a decreasing contribution as the vertical distance increased. In that matter, the vertical height found to have a greater potential impact on reducing the estimated L5/S1 was 30 inches.
Salazar, Nicolas F., "Determination of the range of safe-comfortable lifting postures using the aesthetic ergonomics theory" (2009). Graduate Theses, Dissertations, and Problem Reports. 2887.