Abstract
The purpose of this study is attempting to add static posture adjustment rating points onto KIM checklist to increase its accuracy. KIM checklist is a very simple, accurate workload assessment tool. It has been carefully evaluated and tested in Nordic countries, widely promoted in Taiwan, and is considered as the most promising checklist in musculoskeletal Disorders assessment. Nevertheless, KIM has one shortcoming of not being able to reflect the effect of fatigue due to static posture: For the same total work time, the risk score for static work is the same as dynamic work. However, in theory, static work is more fatiguing than dynamic work : the job cycle (motion period+ rest period) of dynamic work is short, the oxygen debt arising from the motion period can be fully replenished during the following rest period, therefore no lactic acid is accumulated；on the other hand, the job cycle of static work is long, the oxygen debt arising from the motion period can not be fully replenished during the following rest period, significant lactic acid is accumulated over time, and lead to fatigue. For this reason, therefore, this study attempts to add an adjustment rating point to KIM checklist so as to increase its accuracy regarding the assessment of static work. In succeeding to the methodology of KIM LHCver.2 proposed by Yu-Hsun Li(2012), this study takes a step further to investigate the adjustment rating points owing to 30 ° and 45 ° flexion of static posture. An experiment of exhausting fatigue in comparing 5 levels of static work (experiment group) against a dynamic work (control group) was undertaken, the modified Borg-CR10 subjective scale was used to adjust the KIM, by equating the fatigue feeling of the 5 levels of static work against the dynmic work at the moment of exhausting. The designated work was to simulate the assemblage a pipe connector using a 1Kg wrench. The ratio of motion to rest in a work cycle is 2:1, the 5 levels of static works are 0.5 min.:0.25 min., 2 min.:1 min., 5 min.:2.5 min., 10 min.:5 min. and 15 min.:7.5 min.；the dynamic work is 0.2 min.:0.1 min. The maximum sustainable time of dynamic work is set to 2 hours. Ten fit young males was recruited as subjects, pay and reward incentives for participation. Upon the completion of this experiment, the results were graphed and then smoothed using continuous exponential curve to derive the adjustment scores. The results show: for the motion period less than 1 min., 3 min. 6 min. 12 min. or over 12 min. the correspondent adjustment score for 30° flexion is 0 point, 1point, 1 point, 2 points, or 3 points; for 45°flexion is 1 point, 1point, 2 point, 3 points, or 3 points. Finally, the results of this experiment were used to validate 4 field works with static flexion postures, the validation shows that after the incorporation of static posture adjustment scores, the accuracy of KIM LHC is improved.