# Examining the Link between Isokinetic Strength Metrics and Ball Speed in Women's Soccer
## 4 Discussion  
The aim of this study was to determine the isokinetic strength parameters associated with shooting speed in soccer. For this purpose, the relationships between the concentric, eccentric, and isometric torques produced by elite-level female soccer players and their time to reach peak torque and the ball velocities generated during shooting were examined. The conducted analysis found that the relationships between ball velocity and isokinetic strength occurred only during concentric contractions. Accordingly, the isokinetic torques produced by players' dominant side and at 60\({}^{\circ}\)/s angular velocity during the EXT phase were moderately and positively correlated with the ball velocities. When analyzing the biomechanics of shooting, previous reports have indicated no relationship between the angle of approach to the ball and shot accuracy or ball velocity [45]. In soccer, the striking action progresses from proximal to distal, with the extension strength generated at the knee during the final phase creating a propulsive force on the ball [46]. Therefore, the force generated through whole-body dynamics is transferred to the ball at this stage. The obtained result suggests that an increase in knee EXT torque at 60\({}^{\circ}\)/s angular velocity could enhance shot velocity. In soccer, game conditions can influence kicking technique, with the dominant leg being more affected due to factors such as a greater training history and slower adaptation to different conditions compared to the non-dominant leg [47]. As a result, the dominant leg is often preferred for kicks [48,49]. Although the kick is executed primarily with the dominant foot, the contribution of the non-dominant foot is significant due to its role in maintaining balance [48]. The findings demonstrated that the non-dominant extremity's  
Figure 3: Relationships between concentric, eccentric, and isometric strength; time to peak torque; and ball speed. \({}^{*}\)\(p<0.05\). torque production during EXT and FLX at 60\({}^{\circ}\)/s and 180\({}^{\circ}\)/s, and during EXT at 300\({}^{\circ}\)/s angular velocities, was associated with ball speed. This result indicates that strengthening both the EXT and FLX strengths of the non-dominant extremity during a kick could positively impact kick performance. This is because the non-dominant extremity provides essential support for the dominant foot's healthy, balanced, and explosive impact on the ball during a kick. Additionally, as the only extremity in contact with the ground during a kick, the non-dominant extremity is responsible for overall body balance [48, 49]. A balanced stance is crucial for transferring force effectively from the body to the foot and from the foot to the ball [46], and the non-dominant lower extremity contributes to maintaining this balance. Previous studies have emphasized that players' EXT-FLX strength ratios should fall within the 50-80% range to mitigate the risk of imbalanced strength distribution and potential injuries [50, 51, 52, 53, 54]. The examination revealed that a decreased EXT-FLX ratio in the dominant extremity positively influenced ball speed. However, no significant relationship between this ratio and ball speed was found in the non-dominant extremity. Accordingly, while increased EXT strength in the foot used for kicking is crucial, the balanced development of both EXT and FLX strengths in the non-dominant foot is equally important. Considering the dynamic nature of modern soccer and the potential utilization of both feet for kicking, balanced strengthening of both extremities is advisable. The relationships between non-dominant (ND) EXT peak and average torque at 300\({}^{\circ}\)/s angular velocity and ball speeds were determined to be highly significant and positively correlated. This finding stands as the most robust evidence influencing ball speed since the relationships between both average and peak isokinetic strength and ball speed are of high significance.