The purpose of this study is to determine whether different rest intervals and load-repetition combinationswith different frequencies and durations would have an impact on the microtrauma response of the muscleand the development of musculoskeletal disorders (MSDs). Serum Creatine Kinase (CK) level, the physicalresponse measured in this study, is collected before exercise and at days 1, 2, 4, 8 post- eccentric exerciseof the human elbow flexor muscles through phlebotomy and serum analysis.A two-factor (loading and rest interval) factorial regression model is established for muscle microtraumaresponse. The findings of the study would assist in understanding the effect of different rest intervals andload-repetition combinations on muscle microtrauma response and healing process to eccentric exercise,foster injury-prevention recommendations to manufacturing job design in terms of promoting rest intervalswith suitable frequency, as well as force and repetition balance. The regression model could provideguidance to future ergonomic assessment tool design.The results of the study show that higher force with a low repetition frequency leads to greater responsethan lower force with high repetition frequency, when given a predetermined total work time, total rest timeand total work volume. Though not greatly significant, experiment data show that longer rest intervals,although given less frequently, discourages the peak response of muscle microtrauma compared to shorterrest intervals given more frequently, when total work time, rest time and workload are predetermined.
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