چكيده لاتين
In football, the ability to jump for defense and attack is very important. Feather performance can help educators design training programs.The aim of this study was to investigate the relationship between isokinetic and isotonic muscle strength of the knee joint and vertical jump performance of soccer players. This Descriptive study was conducted on 20 elite players under the age of 14 from Foolad Mobarakeh Sepahan Football Club. The subjects first performed three vertical jumps. and then they sat on the Biodex machine under three different instructions. and they performed knee flexion and extension according to three protocols created on the device. The first protocol is isokinetic contraction, concentric mode, and at speeds of 150, 300, and 500 degree per second, The second protocol is isokinetic contraction, eccentric-concentric mode, with speeds of 150 and 300 degree per second, and The third protocol was isotonic contraction, concentric-concentric mode, and resistance of 7 and 14 Newton per square meter. The research questions included the relationship between hamstring and quadriceps muscle strength in both isokinetic and isotonic contraction modes and maximum jump height. The ratio of hamstring to quadriceps strength was also examined.
The results showed that in the isokinetic contraction state, two variables have a significant and moderate relationship with maximum jump height. First, the concentric knee flexion power at an angular velocity of 150 degrees/s (r = 0.479 and p = 0.033). and second, hamstring power to eccentric-concentric quadriceps at an angular velocity of 150 degrees/second (r = 0.431 and p = 0.048). In the isotonic contraction state, seven variables had a significant and moderate relationship with maximum jump height. Which at a resistance of 7 Newton per square meter includes extensional power (r = 0.442 and p = 0.049) and flexural power (r = 0.514 and p = 0.020) and At a resistance of 14 N/m2, these include maximum flexion velocity (r = 0.529 and p = 0.017), hamstring to quadriceps ratio (r = 0.590 and p = 0.006), maximum flexion work (r = 0.476 and p = 0.034), extensor power (r = 0.443 and p = 0.049), and flexor power (r = 0.504 and p = 0.023). Other measured variables had no effect on jump height performance. Overall, this study emphasizes the importance of isokinetic and isotonic muscle power for improving high jump performance. Which can affect the performance of specific sports skills such as heading, catching the ball by the goalkeeper in soccer. This necessitates the use of training and fitness strategies that emphasize isokinetic and isotonic muscle strength.
