Abstract
The purpose of this study was to investigate interrelationship among rebound jump (RJ) ability, vertical velocity and take-off motions at running long jump in higher-grade elementary students. The subjects were 110 boys and 113 girls who were fifth and sixth-graders at elementary school. They were filmed in the takeoff phase, and rebound jump ability (RJ-index = RJ-height / contact time) was measured. The students were dividing into three groups based on RJ ability: Excellent (E), Medium (M) and Poor (P) groups. Measured kinematics during takeoff were compared among these three groups, and relationships between vertical velocity and takeoff motions were studied. The main results were as follows: 1)Boys and girls in E group showed higher touch down, takeoff velocities, vertical velocity at takeoff and longer jumping distance, respectively, than the other groups. Moreover trunk angle during takeoff in E group showed smaller forward inclination, although there was no significant difference all kinematics on knee angle, for either boys or girls.2) E group in the boys showed a greatest takeoff angle among three groups, and a larger decrease in horizontal velocity and a larger generation vertical velocity during latter takeoff phase, and a smaller foot angle displacement than the other groups.3)E group in the girls showed a higher vertical velocity at maximum knee flexion than the other groups.4) The significant correlation in both boys and girls was found between vertical velocity at takeoff and trunk angle at touch down, although no significant correlation was between vertical velocity at takeoff and all sections on knee angle, either boys or girls. The significant correlation in boys was found between vertical velocity at takeoff and foot angular displacement during take-off, and in girls was found between vertical velocity at maximal knee flexion and foot angle at touch down.It is concluded that there was interrelationship RJ ability, vertical velocity and takeoff motions in the higher graders of elementary school.
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