| By using three-dimensional camera analytic method, the author will shoot on the balance beam during women’s all-round final of the national games in 2013. Meanwhile, the stretched back flip action string between Tan Sixin and Yao Jinnan will be compared and analysed from the angle of three-dimensional kinematics. Then, the relevant data of two athletes can be obtained. The author will analyse the key elements of stretched back flip action string by kinematics to provide some references for those athletes who fight in the front line and want to improve.The main conclusions of the research are as follows:The reasons for the failure of Tan Sixin’s action When Tan Sixin pushes off the balance beam by her feet and hands, the vertical velocity is so big. Thus, the stability of her action is not so good. What’s more, Tan Sixin’s flying into the air is not very high. The range of her action is also relatively small. We can see that Tan Sixin’s flying height is lower and the time is shorter from the related data. It is hasty for her to finish the movement because of her time of flip is short, which causes the mistake of falling from the beam. When her right foot falls from the beam, her left foot has already fallen for 0.04 s, which, without any doubt, will lead to the small supporting area of her feet and falling down.During the process,Tan Sixin’s gravity centre is not in the scope of her bearing surface. The deviation of gravity center results in the breaking of the balance. Although she wants to maintain balance by lowering the position of the right arm, the result is not satisfactory.( 2) The reasons for the success of Yao Jinnan’s action Yao Jinnan’s small action is full of rapidness and strength. His horizontal velocity of pushing off the beam by the feet and hands are 1.79 s and 2.06 s respectively. The Horizontal velocity is small, which shows that his strength is greater. So pushing by feet is much more powerful than by hand. No matter which method Yao Jinnan uses, the small vertical velocity can make the stability relatively higher. Yao’s flying height is relatively higher and the amplitude of his movement is fairly large. When he finishes his handspring and steps on the beam with his feet, he gains a positive buffer. This can decrease his knee, ankle and hip Angle. During the copetition, he keeps the vertical velocity for 1.40 m between the beam surface and his highest gravitys center. After leaving from the balance beam, his gravity center increases by the absolute maximum height of 0. 4m. Besides, he keeps the time for 0.66 s from pushing off the beam to stepping on it again. His velocity of stretched back flip is 9.52 rad/s. Yao Jinnan’s flying action is not only high but relatively long. Because his feet fall down on the beam almost at the same time. So it increases the supporting area. Therefore, his body centre of gravity also roughly falls in the range of supporting scope. |
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