KINEMATICAL AND DYNAMICAL ANALYSIS OF LONG JUMP TAKE-OFF: A FOUR CASES STUDY
AbstractINTRODUCTION-The take-off is one of. the most important phases of the long jump. Once there is no available knowledge on kinematic vs. dynamic relationships on the take-of, the purposes of this study were: (i) to analyse the biomechanical variations that occur at take-off; (ii) to establish relationships between kinematic and dynamic variables; (iii) to verify which of the moments of the take-off is more important to the production of the vertical velocity as well as the best result. METHODS~ Subjects for this 4-casesstudy research were well trained jumpers. Each athlete performed 6 trials, all videotaped (JVC-SVHS) in the sagitai plane for kinematical analysis (50 Hz). Simultaneously, dynamic analysis was performed through a Kistler 9218 B force plate (250 Hz). The kinematic parameters studied were: (i) resulting velocity of the center mass (VCM); (ii) horizontal velocity of the center mass (Vx); (iii) vertical velocity of the center mass (Vy); (iv) horizontal velocity of the lead leg knee (VeIK); (v) horizontal velocity of the touchdown foot (VeITd); (vi) loss of horizontal velocity (LVx); (vii) gain of vertical velocity (GVy); (viii) center mass / heel angle in the instants of touchdown and take-off (AngCM-he); (ix) knee angle (AngK); (x) support time (ST); (xi) touchdown distance (TdD); (xii) take-off angle (AngT). The described velocities and angles were determined in the following instants: (i) touchdown; (ii) maximum knee flexion and (iii) take off. The dynamical parameters studied were: fi) vertical impulse (Iz): (ii) maximum vertical force (Fzmax): (iii) time course to achieve maximum vertical force (lH/Fz max); (iv) passive impulse (lzPass}: (v) time course of the passive impulse (lHPass); (vi) active impulse (lzAct); (vii) time course of the active impulse (ßTAct); (viii) horizontal anterior posterior impulse (Iy); (ix) horizontal lateral impulse (Ix) RESULTS-The main results of this study showed that, in all cases, the major loss of the Vx and the major gain of the Vy were observed between the touchdown and the maximum knee flexion We also noticed that the knee of the lead leg has its maximum velocity at the moment of the maximum knee flexion for all subjects. This variables contribute significantly, in all cases, to the increase of the AngK in the take-off instant (psO.05), which is theoretically advantageous to the performance. One other finding was that when the values for AngCM-he in the touchdown and take-off instants were out of the theoretical limits defined by Fischer (1975), a reduced performance was observed. The observation of results also showed: (i) a increased Fzmax was always related with a higher jump length, with a higher % IZPass / IzAct, with a reduction both on ßTAct and ST, despite the correlation analysis did not always provide significant r values. CONCLUSIONS-Long jumpers should pay a special attention to the phase between the touchdown and the maximum knee flexion, where the main production of Vy occurs. There, a reduclion on ST during the take-off should be searched. Attention should also be paid to the values of the AngCM-he during the touchdown. REFERENCES Fischer, R. (1975). Weitsprung. Biomechanische untersuchungen am schweizerischen weitsprungkader mittels filmanalyse und messugen mir der mehrkomponenrenmessplattform. Diplamarbeil in biomechanik, ETH, Zurich.
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