Abstract
It is well known that the leg movement in sprinting is closely related to sprinting velocity for instance, the swinging back velocity of the leg just before the touchdown. Although some suggestions for improvement in leg movement are proposed based on these relationships, it is not easy to improve leg movement only by these suggestions and verbal instructions, because of differences in the interpretation of verbal instructions and conscious emphases of sprinters. The purposes of this study were to clarify the changes in the leg movement under the conditions of various conscious emphases of the leg movement in sprinting and to examine the causes of the changes through the simulation technique. Eighteen male sprinters of the varsity club served as subjects in the experiments. Two-dimensional leg movements of their sprints were recorded with a high-speed video camera. Sixteen kinematic parameters of the hip and knee joints were selected and analyzed in relation to sprinting speed. Three parameters related to the speed were extracted: the maximum flexion angle of the hip, the flexion angle of the knee at the touchdown (TD), and the angular velocity of the hip extension at TD. Five of the subjects in the above experiment were asked to emphasize the leg movements consciously and to sprint as fast as possible. Leg movements emphasized were (a) quick recovery of the leg after the toe off (TO), (b) quick knee flexion after TO, (c) quick swinging back of the leg before TD, and (d) high knees, which were usually used in coaching sprinting. Two-dimensional leg movements recorded in the same manner were compared with the movements peculiar to each subject which were obtained in the first experiment. In the "high knees" condition, it was found that the mean value of the maximum flexion angle of the hip did not increase significantly although increases in the maximum flexion angle of the hip were expected. The changes in the parameters in other conditions were not always the changes expected from the verbal instructions. In addition, simulations of the leg movements during the recovery phase were carried out based on a link segment model in order to examine the reasons why the changes in the leg movements were not uniform. The results of the simulations revealed that changes in the leg movements were affected not only by the magnitude of the changes in the joint torques but also by the timing of the changes of the joint torques. It was also found that the larger knee flexion torque caused the slower knee flexion velocity at TD in the certain condition of the simulation. In conclusion it was suggested that the instructions on the leg movements in sprint were considered and to be suitable to the individual of the sprinter, especially joint torques patterns.
