So far, Japan has won many medals in swimming.But why could the Japanese, who are inferior to overseas players in terms of physique and power, be able to fight evenly?On land, if you kick the ground hard, your body will be pushed forward from the ground with the same force.On the other hand, no matter how hard you water in water, if you do not scratch it well, the force that your body receives will be very weak.There is a possibility that the Japanese can win this watering technique.So what is the most efficient way to get propulsion?In particular, research on the S-shaped stroke and I-shaped stroke of the crawl has been continued for many years, but no conclusion has been reached yet.

　In order to approach this mystery, the group investigated the optimal swimming method by simulation considering the characteristics of the human body such as physique and muscle strength, and the flow of water.As a result, it became clear that the S-shaped stroke is suitable for efficiently obtaining propulsion with less muscle strength, and the I-shaped stroke is suitable for pursuing speed.Furthermore, when examining the actual flow of water around the arm using a swimming robot, it was found that propulsion is generated by different mechanisms between the S-shape and the I-shape.In the simple I-shape, the straight hand movement produces a large forward hydraulic force, while in the S-shape, when the direction of movement of the hand changes, a large diagonal force is momentarily received.

　According to the results of this research, the optimal swimming method varies greatly depending on the swimming distance.In addition, the detailed form may differ slightly depending on the individual's strength, endurance, and physique.In the future, we will proceed with research with the aim of finding the optimal swimming method after considering individual differences.