VARIATION OF SEGMENTAL KINETIC ENERGY DURING THE EXECUTION OF GIANT SWINGS ON THE HORIZONTAL BAR WITH DIFFERENT SPEEDS
Keywords: gymnastics, horizontal bar, kinetic energy
AbstractIntroduction: In the giant swing on the horizontal bar, at the lower part of the rotation the kinetic energy obtained by the body is not enough to return to the initial position, i.e., above the bar, because of mechanical energy losses due to friction and air resistance. Furthermore, many acrobatic movements require a greater speed of swing. The aim of this study was to characterize the variation of segmental and global kinetic energy and to specify how the augmentation of kinetic energy was made possible to allow the performance. Methods and procedures: Three expert gymnasts performed several backward giant swings on the horizontal bar, in three experimental conditions characterized by speed : slow (S), natural (N) and fast (F) speed. Video tape (50 Hz) was used to analyze movements in the sagittal plane, from markers placed on several body segments according to anthropometric studies. Segmental and global kinetic energies were calculated with this mathematical formula : EcT(t) = Si [½miV2 Gi/R ] + Si [½Iiwi 2], R corresponding to the referential of the bar. Results and discussion: In all conditions, the main results were: 1) The rotational component of movement was weak (about 3% of the all kinetic energy), thus the augmentation of the mechanical energy was probably due to the translational component. 2) Concerning the traces of the kinetic energies, the patterns of the upper limbs and trunk were similar but differed with the lower limbs. Thus one can consider the body principally in two parts. 3) The variation of the kinetic energy of the upper body (head, arm, trunk) showed a break in the diminution phase which could explain the augmentation of global kinetic energy. Besides, the minimum and maximum values of the kinetic energy of the upper body changed with the speed of the movement, and, particularly, the amplitude of the minimum values, in augmentation, because of the above-mentioned break, were in correlation with the augmentation of the global mechanical energy. Conclusions: Although the major part of the global kinetic energy was due to the lower limbs, the upper body seems to be responsible of the augmentation of global kinetic energy.
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