Relationship Between Single-Leg Countermovement Jump Height, Technique, and Hip Strength in Elite Handball Players  
[PERSON]  
1 Faculty of Sport, University of Ljubljana, Gortanova 22, SI-100 Ljubljana, Slovenia;  
[EMAIL_ADDRESS] (A.R. ); [EMAIL_ADDRESS] (P.P)  
[PERSON]  
1 Faculty of Sport, University of Ljubljana, Gortanova 22, SI-100 Ljubljana, Slovenia;  
[EMAIL_ADDRESS] (A.R. ); [EMAIL_ADDRESS] (P.P)  
[PERSON]  
2 Faculty of Health Sciences, University of Primorska, Pole 42, SI-6310 Izola, Slovenia; [EMAIL_ADDRESS]  
2 Faculty of Health Sciences, University of Primorska, Pole 42, SI-6310 Izola, Slovenia; nej. Single-leg jumps introduce unique biomechanical and neuromuscular challenges compared to double-leg jumps [7; 11; 12]. Notably, the technical execution of single-leg jumps places greater demands on the hip and trunk musculature [13; 14; 15]. Studies suggest that while hip extensor strength is a key factor in general jump performance [14; 16], single-leg jumps emphasize the roles of hip abductors, external rotators, and lateral trunk flexors [17]. These muscles are crucial for stabilizing the pelvis in the frontal plane, preventing pelvic drop and hip internal rotation and ensuring the proper alignment of the body during the take-off phase [18; 19]. Furthermore, they contribute to effective energy transfer and enhanced jump mechanics by maintaining the alignment of body segments and preventing deviations that could compromise multi-joint force generation [18; 19; 20]. Research on kinetic factors also underscores the complexity of single-leg jumps. For instance, [PERSON] and [PERSON] (2022) [14] reported weak but statistically significant correlations between peak hip extensor torque and single-leg CMJ (SLCMJ) height, suggesting that hip extensor strength may play a role in single-leg jump performance. However, the same study also highlighted moderate correlations between hip extensor strength and double-leg CMJ height, emphasizing that double-leg and single-leg jumps may rely on different neuromuscular strategies. Similarly, studies on hip abductors and lateral trunk flexors have shown their critical role in pelvic stabilization and efficient force transmission during single-leg jumps [17]. Reduced strength in these muscle groups can lead to a shift in the body's center of mass, dynamic knee valgus, and lower jump heights due to compromised force production during propulsion [19]. Furthermore, most studies focus on assessing the influence of knee joint strength on jump performance, while the ankle [21; 22] and the hip [21; 22; 23] are scarcely assessed. This could be a problem, as jumps are a multi-segmental movement, where the coordination between multiple joints influences jump performance. The most important factor for jump success is take-off velocity, which depends on the sequence of movements leading up to take-off. Maximal velocity is determined by joint angular velocities (changes in joint angles over time) and the sequence of segment movements [24]. High angular velocities and a correct, well-timed sequence of movements maximize take-off velocity relative to an individual's abilities. Despite these biomechanical distinctions, the specific kinematic and kinetic factors influencing SLCMJ performance are not yet fully understood. For double-leg CMJs, previous research has identified critical kinematic variables such as trunk inclination (defined as trunk forward lean from the hips to the shoulders) and ankle plantar flexion angle at take-off, which, together, explain over 50% of the variance in jump height [25]. However, no comparable analyses have been conducted for single-leg jumps. This gap in the literature is significant, as single-leg jumps often demand more precise coordination and stabilization due to the unilateral load, which increases the risk of misaligned body segments and suboptimal force application. Therefore, this study seeks to address this gap and build upon previous research.