Aim: The purpose of the study is to determine the relationship between the isokinetic strength of the knee flexor and extensor muscles and vertical jump performance.
Method: 28 elite male volleyball players (Xage = 17,56 ± 1,94 years) were included in the study. Squat and countermovement jump heights of the athletes were obtained using the OptoJump® device. At the same time, the isokinetic muscle strength of flexor and extensor muscles of knee joints of volleyball players was measured concentrically and eccentrically with an Isomed 2000® device. In order to examine the relation between variables; Pearson correlation analysis was used. Regression analysis was used in order to determine the levels of predicting dependent variables of the independent variables which were determined to be correlated with each other.
Results: According to the regression analysis result, quadriceps muscle strength affects 61% of change in squat splash height and 60% of change in countermovement jump height. Hamstring muscle affects 56% of the change in squat jump height and 59% of the change in active jump height. However, when using segmental analysis, it was determined that concentric strength of the left-sided quadriceps muscle at 60º/sec affected squat jump and countermovement jump performance positively on the weak level. The concentric and eccentric muscle strength of quadriceps muscle at 180º/sec angular velocity affected moderately positively the squat jump and countermovement jump performance. At the same time, the right side eccentric contraction of the hamstring muscle at 60 º /sec velocity was found to be an important predictor of squat jump and countermovement jump.
Conclusion: According to the results of the study, it was determined that the concentric and eccentric muscle strength of the quadriceps and hamstring muscles affected both the squat and countermovement performance. We think that to increase the vertical jump performance, the eccentric muscle strength of the right hamstring muscle's and the concentric muscle strength of the left quadriceps muscle at the 60º/sec velocity and the concentric and eccentric muscle strength of the quadriceps muscle of both sides at the 180º / sn angular velocity should be increased.
Keywords: Volleyball, Jump, Muscle Strength, Isokinetic