A BIOMECHANICAL SCIENTIFIC SUPPORT PROGRAM FOR HIGH JUMPERS

  • Jesus Dapena

Abstract

THE ELITE ATHLETE PROJECT - Our laboratory has been collaborating since 1981 with the United States Olympic Committee and USA Track & Field in a series of basic and applied research projects on the biomechanics of high jumping. The basic research serves to further our knowledge of high jumping technique; in the applied research we use the information obtained in the basic research to try to improve the techniques of individual high jumpers. Each line of research provides information that is useful for the other. OVERVIEW OF THE APPLIED RE-SEARCH - For the applied research, we usually film a major competition in June/July, and written reports and instructional videotapes are sent to the athletes in December. The idea is to provide information that will help the athletes to make technique changes from one season to the next, rather than from one competition to the next. The re- ports and videotapes give a detailed biomechanical explanation of standard high jumping technique, followed by an analysis of the technique of each athlete and advice for the correction of defects. The videotapes use computer animation, and show views of each jump from several different directions. METHODOLOGY -During the competitions, the athletes are filmed with two 16mm motion picture cameras shooting at 50 fr/s. The DLT method is used to obtain three-dimensional coordinates of 21 body landmarks in the last two steps of the run-up, the takeoff and the bar clearance. The coordinates are subsequently used to calculate diverse mechanical parameters of the jumps. Several motion sequences are produced for each jump using computer graphics. BASIS FOR THE TECHNIQUE EVALUA- TIONS - The rationale used for the technique evaluations stems from a comprehensive interpretation of the Fosbury-flop style of high jumping based on the research of Dyatchkov (1 968) and Ozolin (1 973), on the basic research of our group (Dapena, 1980a, 1 980b, 1 995; Dapena et al., 1 988,1990), and on the experience accumulated through the analysis of high jumpers at our laboratory in the course of previous applied research. ANALYSIS - We divide the high jump into three phases: the run-up, the takeoff, and the flight or bar clearance. To maximize vertical velocity at the end of the takeoff, the product of the vertical force exerted on the ground and the time during which it is exerted should be as large as possible. This can be maximized by having the center of mass (c.m.) in a low position and traveling at a fast horizontal velocity at the end of the run-up. Statistical information is used to estimate a good combination of the c.m. height and velocity at the end of the run-up for each jumper. The orientation of the longitudinal axis of the support foot during the takeoff phase is used to assess the risk of ankle and foot injury through excessive pro-nation. The backward/forward and Ieft/right angles of lean of the trunk at the start and at the end of the takeoff phase are also measured. They are important because they affect the generation of lift, as well as the generation of angular momentum. The actions of the arms and of the lead leg during the takeoff phase are quantified to judge whether they made an adequate contribution to the generation of vertical velocity. The maximum height that could have been cleared cleanly is estimated for each jump using curvilinear interpolation and computer graphics. It is called the clearance height, and it indicates the true value of the jump. The difference between the clearance height and the peak height reached by the c.m. reflects the effectiveness of the bar clearance. The angular momentum vector of each jump is computed. In conjunction with the action-and-reaction adjustments made by the athlete in the air, it determines the rotations of the athlete over the bar. We study the interrelationships between the angular momentum, the airborne action-and-reaction adjustments, and the effectiveness of the bar c1earance. The possible reasons for problems in the bar clearance are examined. Computer simulation is used 10 facilitate the understanding of the mechanisms that produce the rotations in the air, and to test for viable alternatives in the airborne actions of the jumpers REFERENCES DAPENA, J. Mechanics of translation in the Fosbury-flop. Med. Sei. Sports Exerc. 12:37-44, 1980a. DAPENA, J. Mechanics of rotation in the Fosbury-flop. Med. Sei. Sports Exerc. 12:45-53, 1980b. DAPENA, J. The rotation over the bar in the Fosbury-flop high jump. Track Coach. 132:4201-4210, 1995. DAPENA, J. and C.S. CHUNG. Vertical and radial motions of the body during the takeoff phase of high jurnping. Med. Sei. Sports Exerc 20:290-302, 1988. DAPENA, J., C. McDONALD and J CAPPAERT. A regression analysis of high jumping technique. Int J. Sport Biorneeh. 6:246-261, 1990. DYATCHKOV, V.M. The high jump. Track Technique 34:1059-1074, 1968. OZOUN, N. The high jump takeoff mechanism. Track Technique 52:1668-1671. 1973.