Efeito da posição inicial do salto agachado no desempenho em jogadores de voleibol

Abstract

Vertical jumps are widely used in biomechanical analysis of sports movements as an evaluation tool in the lower limbsstrength. In literature, various knee bending angles have been used by the subjects at the beginning of squat jump and is possible that different positions results in specific performances. Some studies have attempted to investigate the effect of different initial angles of knee flexion in the behavior of dynamic variables and its relationship with the jump height, however, the results are controversial.The aim of this study was to verify the effect of three different initial positions on the squat jump performance and on the bilateral strength asymmetry of the lower limbs, measured by a force platform. Fifteen male junior volleyball players (15years old) were familiarized with the jump technique and performed three random squat jumps with maximum intensity at each squat position: SA90° (90° of knee flexion), SA120° (120° of knee flexion) and SAAuto (self-selected position - 99,06°). The performance variables analyzed were: jump height, peak force, impulse and take-off velocity. To verify bilateral strength asymmetry of the lower limbs, the Limb Symmetry Índex was calculated for peak force and impulse. For the jump height, there was no difference between SA90° and SAAuto positions (0,30 m) and the height reached for these positions were greater than the one reached for the SA120° position (0,25). As the angle of knee flexion has been reduced, impulse increased (SA90°= SAAuto> SA120°) and the peak force significantly reduced (SA90°< SAAuto< SA120°). For the bilateral strength asymmetry of the lower limbs, the results for peak force and impulse were that SAAuto position has the smallest difference between limbs. In conclusion, the study found that the starting position could affect the jump performance and the bilateral strength asymmetry.