## 4 Discussion  
This is the first study investigating the relationship between hip abductor muscles strength and frontal plane kinematics in HB athletes. The results of this study confirmed the hypothesis raised and reported a very strong relationship between the hip abductor muscles strength and the pelvic drop, femoral adduction, and knee valgus in male HB athletes. A negative relationship was found between hip abductor muscles strength and pelvic drop angle, while a positive relationship was identified with the femoral adduction angle. Thus, higher strength levels were related to less pelvic drop and femoral adduction in HB athletes. The results achieved in this study agree with those found by previous authors [18; 45; 46]. [PERSON] et al. [45] concluded that hip abductor strength explained 17% of contralateral pelvic drop and 21% of femoral adduction angle during walking in patients with knee osteoarthritis. [PERSON] et al. [46] reported that hip abductor muscles, knee flexor muscles, and ankle inversion muscles strength explained 34.4% of contralateral pelvic drop during walking in patients with knee osteoarthritis. [PERSON] et al. [18] found a statistically significant reduction in contralateral pelvic drop and femoral adduction during a single-leg squat after a hip strengthening program in runners. Other studies showed no associations between hip muscle abductors strength and pelvis and hip kinematics. However, the task requested was not a single-leg task, which could lead to conflicting results [47; 48]. Nevertheless, this is the first study showing a very strong correlation among HB athletes. The results of this study also showed a positive relationship between hip abduction strength and dynamic knee valgus angle in HB athletes; greater strength was associated with less dynamic valgus. Previous studies support the hypothesis concerning the relationship between hip muscles and dynamic knee valgus in athletes using a 2D motion capture [19; 49]. [PERSON] et al. [49] showed a significant positive correlation between external rotation hip strength and the dynamic knee valgus in soccer, basketball, and volleyball athletes during single-leg squat. [PERSON] et al. [19] reported a decrease in dynamic knee valgus at dynamic landing after applying a hip muscle strengthening protocol in soccer athletes. [PERSON] et al. [50] reported similar results using a 3D motion capture system, showing a moderate correlation between hip muscles and knee kinematics in basketball athletes during single-legged medial drop. These findings suggest that using 2D software Kinovea may present similar results compared to a 3D system. Previous studies have analyzed the association between 2D software Kinovea and a 3D system (@VICON Motion System, Oxford, UK) for measuring hip, knee, and ankle angles during walking, and found a reasonable association with errors between 2\({}^{\circ}\) and 5\({}^{\circ}\) between both systems [51]. Thus, 2D systems may elicit similar results to 3D systems, and could be used in future studies and training programs to analyze injury risk. Lower limb kinematics in the frontal plane seems to play a role in an athlete's development of lower limb injuries [5; 6; 7; 8; 11; 12; 13]. This study evidences its relationship with the strength of the hip abductor muscles, and several authors suggest that these variables are modifiable with a physical therapy intervention based on strengthening [19; 49; 50]. Thus, its evaluation and management in clinical practice should be considered. In this sense, 2D motion capture systems for kinematic assessment appear to be reliable and accessible to clinicians. In addition, previous studies included runners [18; 44; 45], soccer [19; 49], basketball [49; 50], and volleyball [49] athletes, but this is the first study focused on HB athletes. Since HB showed a higher risk of injury than these sports [1], it is necessary to under