Salto em profundidade: análise dos deslocamentos em queda livre do centro de gravidade em quatro alturas de banco de lançamento

Abstract

The drop jump is a technique that uses the Stretch-Shortening Cycle (SSC) for lower limbs, in which the subject drops from a height, landing without touching the heels and then performing a jump with maximum effort. Increases in box height equal or greater than 20 cm are commonly used and can be a problem for a precise control of mechanical and temporal loads in drop jump training. Another problem in evaluatingperformance with drop jump is considering the box height as the free falling displacement of the Center of Gravity (CG), which can lead to error in estimating the speed of the CG before the first contact, and then miscalculations of vertical displacements by the impulse method. Therefore, the objectives of this study were to compare through the impulse method the free falling displacement of the CG obtained from four box heights (20, 30, 40 and 50 cm) to check if the increments of 10 cm in the box height are appropriate for the evaluation and training with drop jump, and to compare the real free falling displacement of the CG with their respective box height. Participated in this study 22 male subjects aged between 18 and 25 years (1.72 m SD 0.11 m; 73.9 kg, SD 9.1 kg; 21.3 years SD 2.2 years). Subjects attended two assessment sessions 48 hours apart. The first was considered a familiarization session and the data from the second session were used for analysis. Data analysis showed that: the free falling displacements of the CG were significantly different (F = 413. 3378, p <0. 0001), the free falling displacements of the CG were significantly different from their respective box heights (p < 0. 001 for all times). It can be concluded that increases of 10 cm in box height are adequate and are indicated when the objective is to control more precisely the load in the assessment and training with drop jump. The free falling displacements of the CG are different from the respective box heights, excluding the possibility of using the height of the box as a criterion to estimate the speed before the first contact.