Visiting Researcher: Yoshiyuki Mochizuki Article List>> ******* Biomechanical simulation for sports motion analysis The purpose of this study is to establish the method of a new scientific analysis for studying sports motion by using the mathematical method of modeling the physical function of humans, and optimized and optimization-applied computer simulation. As the subjects of this study, we selected pitching and long-distance throwing (Fig. 1 and Fig. 2) along with batting (Figs. 3 and 4) motions. In the study of pitching motion, we carried out a detailed investigation of a smooth pitching motion and demonstrated that the squared sum of the first- and second-order joint torque functions is important for realizing smoothness in movement not only in terms of torque but also in terms of the spatial trajectory. In addition, we conducted a dynamic simulation analysis to study how the pitching motion is influenced by the mass and shape of the upper limb and by the mass and shape of the ball. Regarding the influence of the mass and shape of the upper limb, the experimental data demonstrated that the pitching motion should be improved for increasing the ball speed, when the pitcher’s muscle has been strengthened through muscle training. Conversely, this suggests that the increase in the muscle strength can act as a trigger to improve the pitching motion. Regarding the influence of the mass and shape of the ball, we conducted an experiment using several types of balls used in sports other than baseball. The data exhibited specific features in the loop of the trajectory drawn by the end point of the hand, which indicates that pitching motion can be classified into two groups. From this result, we can specify important points to be kept in mind when providing training in pitching motion with a ball used in other sports. Fig. 1 Fig. 2 In the study of long-distance throwing, we conducted an analysis of the influence of the throwing angle and clarified the mechanism of long-distance throwing motion from the aspects of both dynamics and kinematics. For example, we confirmed that the releasing point of the ball is advanced when the throwing angle is increased. In addition, the torque of the shoulder joint acts on the upper limb to move it downward and backward at the beginning of a loop drawn by the end point of the hand and to move rapidly forward from the lowest point of the loop. Further, we studied a training process in which several objectives were set for proficiency. Selecting the long-distance throwing motion as a specific example, we investigated how convergence behavior changes when the level of importance of each of these objectives is dynamically changed during training. As a result, we obtained new findings on the training of sports motion. According to the findings, when the level of importance of each objective from among several objectives is changed dynamically during training, the motion learned from the training changes depending on the sequence of objectives in the order of level of importance. The experimental data provided an interesting result: the various pitching motions learned from the training with a different sequence of objectives converge to three styles of long-distance throwing that are already known. These are the side-hand style typified by disc throwing; the over-hand style, which is the same style as the initial motion; and the quarter-hand style, which is an intermediate between the abovementioned two types. Therefore, when several objectives are set in training, the sequence of objectives in the order of level of importance is important. This suggests that subtle differences in motion observed in the case of real players can arise not only from their physical factors but also from the training sequence. In the study of batting motion, we conducted a dynamic analysis and optimized batting motion by constructing a mathematical model and performing a simulation experiment with a focus on the flexion-extension-flexion phenomenon as the bat-upper limb interaction. The results indicate that two inertial forces—centrifugal force and Coriolis force—play an important role, while gravity has a small influence. Further, through the data of the optimized simulation, we demonstrated that there exists an optimal batting motion that can restrict the stress exerted on the wrist joint to the maximum possible extent, and clarified a mechanism of batting motion that focuses on the flexion-extension-flexion phenomenon. Fig. 3 Fig. 4 Fig. 5 Through the abovementioned specific analyses, we demonstrated that the method used in this study is very effective as a complement to empirical approaches to sports motion. Furthermore, when the method is regarded as a generating technique of optimal sports motion, it can contribute significantly to entertainment and education industries when combined with the visualization technique of sports motion (Fig. 5).