The purpose of this study was to estimate the propulsive force of the hand, and the joint torque generated in the arm pull during the breaststroke swimming. Subject was one Japanese male elite swimmer in breaststroke. The swimming motion in breaststroke of the swimmer was recorded by using four synchronized video cameras. Ten landmarks on the right upper body were digitized at 60 Hz and their three-dimensional coordinates were obtained using a DLT method. The fluid force acting on the hand was calculated using the drag and lift coefficients by Schleihauf ¹²⁾. The arm was modeled as a three-links kinetic chain composed of the upper arm, forearm and hand, and angular velocities and joint torques were computed. Lift force was dominant rather than drag, which were generated by the arm pull motion. Large torque was observed in wrist palmar flexion, elbow flexion and shoulder horizontal abduction and horizontal adduction.

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The purpose of this study was to determine the critical combination of all four elements which expressed the threshold of fatigue in interval training by using the critical swimming velocity that was an effective index when we set training strength, and to make a model that we could use as an indicator when we prescribed the training menu that accepted an individual. Only for 50m at repeated distance, we set a different rest time in three phases of different swimming velocity each and performed a test to let subjects repeat exercise up to fatigue. In addition, we measured the maximum repetitions that could repeat exercise. As a result, it became clear that the maximum repetitions that could repeat interval training without reaching fatigue in a certain swimming velocity was in proportion to the total rest time. And then, we were able to see the relations with the repetitions and the rest time in three phases of different swimming velocity. Furthermore, we were able to get relations with the rest time and the swimming velocity which expressed the threshold of fatigue in the arbitrary repetitions by fixing the repetitions. It was concluded that we were able to determine the critical combination from the above-mentioned by this study.

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In this paper, clarification of the fastest stroke in freestyle swimming by simulation was attempted. That is, the front crawl swimming was optimized for swimming speed and propulsive efficiency using Genetic Algorithm (GA). First, GA was integrated into our swimming human simulation model SWUM, which was developed for analyzing swimming motion. The design variables in the optimization were joint angles of the upper limbs. In addition, in order to obtain reasonable results and to make the computation more efficient, three constraints were imposed on the optimizing algorithm. Then, the fastest and most efficient strokes were numerically solved. Both the obtained strokes have their own features distinguished from the conventional strokes. From the analyses of the joint torque and fluid force, it was found that the fastest stroke is explained as 'full power during whole stroke', while the most efficient as 'full power in efficient moment'

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