Influence of Ground Reaction Forces and Joint Velocities on Kicking Velocity

Introduction: Kicking is a vital component in the game of soccer. One major factor that influences the success of a scoring attempt is ball velocity. Ground reaction force (GRF) and joint velocities of the lower extremities are variables of interest for increasing kicking velocity. Previous studies have shown exercise programs used to strengthen the muscles used in kicking have been successful in increasing kicking velocity (Manolopoulos, et al., 2013).[GJR1] To date, no known studies have analyzed the specific relationship between GRF, joint velocity and kicking velocity. Purpose: The goal of this pilot study was to analyze the influence of ground reaction forces and joint velocities on kicking velocity. Methods: Four female Division II collegiate soccer players [GJR2] completed 3 instep soccer kicks [GJR3] using their dominant, right leg. Their motion was captured using the Cortex 8.1 Motion Analysis Software. Ball velocity, right and left anterior superior iliac spine (ASIS) and right and left ankle velocities were calculated using the motion analysis software. Ground reaction forces from the plant leg were also measured using force plate data from the Cortex software. Bivariate Pearson correlations with 0.95 confidence intervals were computed using SPSS version 28 for the resultant velocities of the right and left ASIS, right and left ankles, and the velocity of the ball. They were also calculated for the peak GRF in the anteroposterior (X), mediolateral (Y) and vertical (Z) directions and ball velocity. A correlation value of \u3e0.800 or \u3c -0.800 was considered significant. Results: Significant correlations were found between peak resultant ball velocity and GRF in the X direction (-0.907), GRF in the Y direction (0.867), R ASIS velocity (0.950), R ankle velocity (0.855), and L ankle velocity (0.977). No significant correlations were found between peak resultant ball velocity and GRF in the Z direction (0.788), or peak resultant ball velocity and peak joint velocity of the L ASIS (0.692). Conclusion: Braking force of the planting leg is shown to correlate significantly with kicking velocity. Although high braking force allows for a faster ball, this can have other implications to injury [GJR4] (Ball, 2012; Jones & Graham-Smith, 2016). Linear velocity of the hip also allows for greater ball velocity. As a pilot study, this study lacks the statistical power to extrapolate the information to larger populations. Therefore, additional studies are needed to further investigate the relationships between kicking mechanics and the resulting ball velocity

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