Correlation Between Quadriceps and Hamstring Isokinetic Strength to Ball Velocity During a Soccer Kick

When kicking a soccer ball, large forces are generated by the quadriceps and hamstring muscles that extend and flex the knee. The angular acceleration[GJR1] at this joint and the torques produced are[GJR2] related. PURPOSE: The goal of this pilot study was to explore the relationship between isokinetic strength[GJR3] of the quadriceps and hamstring muscles to velocity of a kicked soccer ball and determine if isokinetic testing of quadriceps and hamstring strength can predict soccer ball velocity during a kick. Methods: Four female NCAA Division II soccer athletes completed maximal effort knee flexion and extension at three isokinetic speeds, 60°/second, 180°/second, and 300°/second using the Biodex 3 Isokinetic Dynamometer. Cortex 8.1 Motion Analysis Software was used to record three maximal kicks with the dominant leg. Bivariate Pearson correlation coefficients were calculated between both data sets using SPSS version 28. Results: Ball velocity was significantly and positively correlated with Right Leg Flexion Acceleration time at 60°/second(r= 0.860),[GJR4] Left Leg Extension Acceleration at 180°/second (r= 0.950), and Left Leg Extension Acceleration at 300°/second (r= 0.915). Two significant negative relationships were discovered between ball velocity and left leg extension acceleration at 300°/second (r= -0.950), and left angle of peak extension torque at 300°/second (r= - 0.915). Conclusion: The ability to quickly accelerate the non-kicking leg to extension combined with the ability to reach angle of peak extension torque is associated with the ability to quickly stabilize the plant leg. Flexion of the kicking leg at a lower angular velocity corresponds with a higher force production and when combined with a positive correlation to ball velocity, suggests increased loading of the kicking leg prior to ball contact. Lastly, the negative correlation between ball velocity and kicking-leg extension acceleration would suggest that faster acceleration leads to increased ball velocity. Because of this, isokinetic testing of the quadricep and hamstring strength is likely a good predictor of kicking velocity. Further testing is required to determine if present correlations are applicable to other populations of soccer athletes, which can affect training and return-to-play practices