Impact of Loading and Rest Intervals on Muscle Microtrauma

The purpose of this study is to determine whether different rest intervals and load-repetition combinations with different frequencies and durations would have an impact on the microtrauma response of the muscle and the development of musculoskeletal disorders (MSDs). Serum Creatine Kinase (CK) level, the physical response measured in this study, is collected before exercise and at days 1, 2, 4, 8 post- eccentric exercise of the human elbow flexor muscles through phlebotomy and serum analysis. A two-factor (loading and rest interval) factorial regression model is established for muscle microtrauma response. The findings of the study would assist in understanding the effect of different rest intervals and load-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 intervals with suitable frequency, as well as force and repetition balance. The regression model could provide guidance to future ergonomic assessment tool design. The results of the study show that higher force with a low repetition frequency leads to greater response than lower force with high repetition frequency, when given a predetermined total work time, total rest time and 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 shorter rest intervals given more frequently, when total work time, rest time and workload are predetermined.