We tested the combined effects of work schedule and task factors on upper-extremity fatigue in the laboratory during 8-h and 12-h shift schedules. Participants performed a simulated manual assembly task at three repetition rates and three torque loads and self-adjusted their work cycle duration to maintain fatigue at moderate levels. Work cycle durations decreased with increases in both load level and repetition rate. Fatigue was observed more quickly with increasing time on shifts and during night shifts compared with day shifts. Work schedule effects were most apparent at lighter workloads, with minimal differences at higher workloads. The highest fatigue levels were observed during 12-h night shifts, with similar levels reached by the end of both the week of 8-h night shifts and the week of 12-h day shifts. Overall durations were 20%-30% shorter than in previous short-term studies, which was likely a result of the more realistic work schedules used in this study. Results from this study could be applied to the design of work-rest schedules for manual tasks involving the upper extremities.
The aim of this project is to develop a questionnaire for identifying jobs associated with the risk factors for musculoskeletal cumulative trauma, including repetition, force, and whole-body exertion. The questionnaire, designed to be minimally ambiguous and generalizable across occupations, contains familiar, everyday activities (e.g., walking, slicing a potato). The activities serve as perceptual-cognitive "anchors" against which work activities are judged to determine level of exposure to musculoskeletal stress.During the first phase of questionnaire development, ergonomics experts generated common activities involving repetition, force, or whole-body exertion. Duriag the second phase, workers rated their familiarity with the activities using a scale ranging from 1 (no familiarity) to 7 (high familiarity). One-hundred fourteen activities rated as very familiar (i.e., a rating of 5 or greater) by at least 75%
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