The efficiency priority working environments without considering the physical property of workers make the workload of workers increased and make the efficiency of workers decreased unintentionally. Therefore, it is necessary for plant managers to design the safe and efficient working environment considering the physical characteristic. The objective of this study is to propose the method to determine the optimal working condition considering the physical characteristic of each worker in the lifting operation. To this end, this study suggested the method to simulate working condition considering muscle forces during motion in the lifting operation, and evaluated the muscle force of each muscle during motion using the musculo-skeletal model considering the role of antagonistic muscles and biarticular muscle. Accordingly, the optimized workable weight for each worker was estimated. As a result, this study can be used to simulate the optimized working condition considering the physical characteristics including muscle forces. This study may help the plant manager to design the working condition and determine personnel distribution according to physical characteristic of worker.