WORK SCHEDULE AND TASK FACTORS IN UPPER-EXTREMITY FATIGUE

We tested the combined effects of work schedule and task factors on up per-extremity fatigue in the laboratory during 8-h and 12-h shift sche dules. Participants performed a simulated manual assembly task at thre e repetition rates and three torque loads and self-adjusted their work cycle duration to maintain fatigue at moderate levels. Work cycle dur ations 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 w ere most apparent at lighter workloads, with minimal differences at hi gher workloads. The highest fatigue levels were observed during 12-h n ight shifts, with similar levels reached by the end of both the week o f 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 li kely 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 s chedules for manual tasks involving the upper extremities.