INTRODUCTION: There are many mechanical problems to be solved in human swimming. For these problems, the authors have developed a simulation model, "SWUM," (Nakashima et al., 2007) and a free software "Swumsuit" as the implementation of SWUM. Since SWUM was reported in the last symposium, major extensions have been successively made on it, such as optimizing calculation, musculoskeletal simulation, and multi agent/object simulation, in order to extend the capability of analysis. In this paper, these extensions are explained and the various recent results from their implementation are presented in order to show their validity and usefulness. METHODS: All analyses in this paper were carried out using SWUM. The first extension of SWUM was for the optimizing calculation. In the optimizing calculation, a single simulation of time integration is repeated changing the various design variables until a given objective function is maximized. The second extension was the musculoskeletal simulation. The whole body musculoskeletal model with 458 muscles was employed. The third extension was "multi agent/object simulation." "Multi agents" means multiple swimmers and "multi objects" means implements for swimming such as fins, a starting block, the pool wall, and so on. RESULTS AND DISCUSSION: A simulation example of the optimization of arm stroke in freestyle swimming was presented in the paper. It was found that the thrust by the hand had two clear peaks when pulling (t = 0.29, t is nondimensional time) and pushing (t = 0.54) the water. For the musculoskeletal simulation, an example of the simulated and experimental results for the breaststroke was shown. It was found that the upper limb muscles were activated at the hand stroke, and that the lower limb muscles were activated at the kick in the simulation. As the examples of the multi agent/object simulation, simple synchronized swimming by three swimmers, monofin swimming, and the shooting motion in water polo were presented respectively. In the simulation of shooting motion, the velocity of the shot ball was 13.5m/s. In future studies, various mechanical problems in swimming and aquatic activities will be analyzed by the present extensions.
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