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The aim of this research is to establish the quantitative evaluation method for lifting task and to clarify the safety posture and optimal motion. This paper examines the motion from three kinds of start-on posture with the acceptance rate. Operation-A starts from the pose-A in which the knee is extended to the maximum. Operation-B starts from the pose-B in which the knee is flexed to the maximum and the upper body is raised as much as possible. Operation-C starts from the pose-C in which the knee is flexed at almost right-angled and the upper body is raised. The acceptance rate is the estimated population rate who can permit the joint moment during the lifting operation, based on the presumed moment and the coefficient of variation of the acceptable marginal moment on each joint. The compressive force on lumbar vertebrae computed from the L5/S1 joint moment at 85 [%] of the acceptance rate (about AV.-1SD) has not been over the standard value of a previous research. So we have set 85[%] as the safety standard acceptance rate, then we settled judging-A (over 95[%], recommended), judging-B (85-95[%], should note), and judging-C (under 85[%], should modify). Although the ankle joint on operation-A and the knee joint on operation-B is judged as C rank, every joint on operation-C shows high acceptance rate. So the validity of operation-C has been clarified quantitatively.

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