Effet de l'instruction sur la régulation de la raideur des membres inférieurs lors de sauts de contre-haut

Abstract

Goal. – We tested in this study the possibility of influencing leg stiffness through instructions on the knee flexion in drop jump (30 and 60 cm). Method. – Twelve basket players were instructed to jump with three different instructions: 1) “jump as high as you can”; 2) jump high with a larger knee flexion at touch-down and 3) jump high with a smaller knee flexion at touch-down. The ground reaction force were measured with an AMTI force plate (500 Hz). The kinematics of the jump was recorded using two digital cameras (50 Hz). Results. – The results show that the ground reaction force pattern depended more on the instruction than on the height of the box. The active peak decreased from 6 times the body weight (BW) to 2.9 times BW. Bending the knee appears to be an efficient strategy to increase the leg stiffness [ R =0.86; P <0.05]. Conclusion. – The instructions high knee flexion decreases the leg stiffness. The same vertical jump performance could be achieved with different values of stiffness. The maximum knee flexion does not modify the vertical performance.