The purpose of this master's thesis is to investigate possible connections and the impact of strength parameters of knee extensors and flexors on the speed and change of direction ability in soccer players. The study was conducted on a sample of 41 soccer players from the first U17 and the first and second U19 National leagues of Slovenia. Measurements of isokinetic strength of knee extensors and flexors (maximum isokinetic torque), functional field tests (single-leg jumps, measurements of change of direction ability, and speed), and measurements of eccentric hamstring strength on the Nordic hamstring device were performed. The aim of the research is to determine which predictive variables are related to speed and change of direction ability and to what extent they influence speed and change of direction ability.
Using Pearson's correlation coefficients at a 5% significance level, we found a negative and weak correlation between test 180 and single-leg long jump with the left leg (r = -0.34). For the right leg, we found a positive and weak correlation between the change of direction deficit, expressed in time (CODD), and percentage (CODD%) in a 90° turn and single-leg long jump (r = 0.31 and r = 0.31), between CODD 180° %, single-leg long jump (r = 0.33), and concentric knee flexion at 180°/s (0.38), and between CODD 180° and concentric knee flexion at 180°/s (r = 0.35). We also found negative and weak to moderate correlations between the 10 and 30 meter sprints, concentric knee flexion (r = -0.37 and r = -0.34), single-leg long jump (r = -0.48 and r = -0.59), and side single-leg jump (r = -0.39 and r = -0.47). The 10 meter sprint is weakly and negatively correlated with the maximum torque ratio between knee extension and flexion at 180°/s (r = -0.32).
According to the results of multiple regression analyses for the running time with a 180° direction change (COD 180°) with the left leg, the single-leg long jump proved to be the best predictive variable, explaining 12 % of the variance. CODD 90° and CODD 90° % are also best explained by the single-leg long jump, with 10 % of the variance. The best predictive variable for CODD 180° and CODD 180° % with the right leg is concentric knee flexion at 180°/s, explaining 12 % and 14% of the variance respectively. The best predictive variable for 10 and 30 meter sprint is the single-leg long jump, explaining 23 % and 35 % of the variance, respectively.
The maximum strength of knee extensors and flexors has a limited impact on speed and running with a change of direction. We found that the maximum and fast power of the lower limbs affect the (in)efficiency of executing turns. Stronger and more explosive players had relatively larger time losses in executing turns with the right leg.
|
