Short-cycle overhead work and shoulder girdle muscle fatigue [An article from: International Journal of Industrial Ergonomics] Review
This digital document is a journal article from International Journal of Industrial Ergonomics, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.
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The objective of this research was to determine shoulder girdle fatigue for different combinations of weight of workpieces, weight of hand-tools, shoulder postures, arm up time and arm down time that are commonly used in automotive assembly operations. Both objective [surface electromyography (sEMG)] and subjective measures (ratings of perceived exertion, (RPE), fatigue and pain) were used to assess stress, fatigue and pain in the shoulder girdle. Ten healthy young female subjects participated in a laboratory experiment that consisted of a simulation of common automotive assembly job tasks. The simulation consisted of four tasks in a 1-min job-cycle. Each cycle was repeated 50 times. The four tasks were varied with different predetermined combinations of two weights (W"1 signifying a workpiece and W"2 signifying the hand-tool weight), three exertion times and three shoulder postures. W"1 was either 1.36 or 2.73kg (3 and 6lb), and W"2 was 0.45, 0.91 or 1.82kg (1, 2 and 4lb). Exertion time was with the arm up for 2 seconds and down for 2s (2-2) for ten exertions per minute, arm 3s up and 3s down (3-3) for seven exertions/min, or arm 5s up and 3s down (5-3) for five exertions/min. Each cycle finished with an 8-10s rest phase to complete a 1-min cycle time. The posture angles were shoulder flexion of 60^o, 90^o and 120^o combined with an included elbow angle of 90^o, 120^o and 150^o, respectively. Experimental combinations (n=54) were randomly selected. Response variables were recorded in the first minute and every 5min thereafter for 50min. The response variables included sEMG, RPE, fatigue and pain in the shoulder girdle. All subjects were able to perform all combinations with the lowest weights; however, in the more extreme postures, a few subjects prematurely terminated the experiments due to fatigue and/or pain. RPEs, as compared to sEMG data, appeared more sensitive and consistent. An analysis of variance showed that all four variables (workpiece weight (W"1), tool weight (W"2), arm up and down time, exertion time and shoulder posture) were statistically significant (p=<0.01), although the tool weight and workpiece weight were most predictive of capabilities. As expected, the RPE, fatigue and pain increased with an increase in the weights of the workpiece (W"1) and hand tool (W"2). Guidelines for acceptable workloads are provided. Relevance to Industry: Combinations of weights, exertion time and shoulder posture that cause excessive fatigue are important for designing overhead work and hand-tools. The data reported provide a set of such data for female subjects.
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Aug 22, 2011 17:59:03
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