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Biomechanical analysis of the takeoff in the standing long jump. Kinetics of maximal and sub-maximal jumps

Abstract:

The standing long jump (SLJ) is often used to test the explosive force of the lower extremities. Compared to other tests such as the counter- movement and squat jumps, the good reproducibility and validity of the standing long jump have been assessed in some studies. In spite of all, several authors criticise it (SLJ) because of its high technical complexity, which may invalidate the results achieved by persons with no prior of jump training. So as to observe the efficacy of the jump from a kinetic point of view, an experiment has been designed. Nine young subjects (23.1±1.9 years old), national volleyball players, performed the SLJ and jumps at 35%, 40%, 50%, 55%, 65%, 70% and 80% of the distance achieved in the maximal jump, all of them taking off on a force platform (Dinascam 600M) in order to assess the ground reaction force. From the sub-maximal jumps to the maximal ones, the values of the maximal force in the front-back axis (Fx max:) increase from 471.51±78.1 N in the jump at 35% to 766.64±20.06 N in the 100% one. Contrary to expectations, the values of the maximal force in the vertical axis (Fz(MAX)) decrease from 1282.61±149.54 N to 1008.18±151.62 N. Thus, the Fz(MAX) is not a discriminating variable of the explosive force in the SLJ, as it is in the SJ and CMJ. Moreover, the value of the resultant maximal force (Fz(MAX)) also decreases when the percentage of the jump increases from 2043.73±205.44 N in the jump at 35% to 1766.28±241.19 in the maximal jump. In comparison to the impulses in the vertical axis, the impulses in the frontback axis (1(x)), which increase from 133.73±20.8 N (35%) to 258.98±26.51 N (100%), the drag impulses (1(F)) increase from 64.05±14.35 N to 90.13±15.88 N and the acceleration impulses (1(A)) slightly decrease from 140.34±18.38 N to 133.1±26.17 N. So as to preserve the kinetic pattern of the SLJ, it is necessary to perform a jump at 80% at least of the distance of a maximal jump, which can be applied to training.