This was a cross-sectional study conducted in a single measurement session, with the total duration of approximately 45 min. Participants performed maximal voluntary isometric contractions (MVICs) of the hip and lateral trunk muscles, explosive isometric contractions of the hip muscles, and single-leg horizontal jumps for distance with both limbs. All tests were performed in a randomized order. Prior to testing, participants completed a standardized warm-up protocol supervised by a qualified member of the research team. The warm-up consisted of 10 min of jogging, followed by mobility exercises for the arms, hips, knees, and ankles (10 repetitions each). Participants then performed dynamic stretching exercises targeting the hip flexors, knee extensors, knee flexors, and ankle plantar flexors (10 repetitions each). The warm-up concluded with resistance exercises, including heel raises, squats, and crunches (10 repetitions each). All tests were conducted in a laboratory setting with a parquet floor under controlled environmental conditions (ambient temperature: 21 °C; relative humidity 30%–35%) and were performed by two sports scientists (PhDs) with more than five years of experience in neuromuscular testing.

An a priori statistical power analysis was conducted to determine the minimum sample size required for the study using G*Power software (version 3.1; Faul et al., Universität Kiel, Germany). The analysis was based on findings reported by Kollock et al. (22), who observed an average coefficient of determination of r² = 0.18 (corresponding to r = 0.42) between hip abduction, adduction, flexion, and extension strength and single-leg horizontal jump distance in recreationally active men. Assuming a two-tailed correlation analysis with an alpha level of.05 and a statistical power of 0.80 (β = 0.20), the analysis indicated that a minimum of 43 participants was required to reliably detect correlations of comparable magnitude in the present study. To be conservative and to account for the larger number of correlations examined, we ultimately included 80 elite male handball players from the first national Slovenian league, each with at least 10 years of training experience. Their mean (standard deviation) age, height, and body mass were 21.8 (3.9) years, 1.90 (0.06) m, and 92.0 (9.6) kg, respectively. All players were actively engaged in regular handball training, practicing at least five times per week with their clubs over the previous five years, including both pre-season and competitive periods, with approximately 30 official matches (±3) per season. Approximately 70% of the participants also performed regular resistance or preventive training sessions twice per week during this period. The inclusion criteria required participants to be free from musculoskeletal injuries or pain syndromes for at least one week prior to the measurement session, as well as free from any medical conditions that could be aggravated by the testing procedures. In agreement with the coaches, participants were instructed to avoid strenuous activity for two days prior to testing. No dietary restrictions were required. Before data collection, they were fully informed about the study protocol and signed an informed consent form. For underage participants, their parents or legal guardians signed the consent on their behalf. They wore only tight-fitting shorts (mid-thigh length), low-ankle socks, and low-ankle training shoes of their choice to minimize any influence on the testing process. Since single-leg horizontal jumps were routinely performed as part of their physical preparation in regular training, no additional familiarization session was necessary. Testing was conducted during the pre-season period.

Statistical analyses were performed with SPSS (version 25.0, SPSS Inc., Chicago, USA). Descriptive statistics are reported as mean (standard deviation) and range (minimum–maximum). The normality of the raw data distribution was verified with the Shapiro–Wilk's test. In the first phase of the analysis, intra-session reliability of the SLHJ variables across the three repetitions was calculated using the intraclass correlation coefficient [ICC_2.k with 95% confidence intervals (CI)]. According to the latest guidelines, ICC_2.k values were interpreted as follows: values <0.50 indicate poor reliability, 0.50 ≤ ICC_2.k < 0.75 indicate moderate reliability, 0.75 ≤ ICC_2.k < 0.90 indicate good reliability, and ICC_2.k ≥ 0.90 indicate excellent reliability (27). Absolute reliability was assessed using the coefficient of variance (CV), with values ≤10% considered acceptable (28). The statistical significance of mean differences among the three repetitions was analysed using a repeated-measures one-way analysis of variance (ANOVA), followed by Tukey's HSD post hoc test for pairwise comparisons. In the second phase of the analysis, the strength of linear relationships between hip and trunk strength variables and SLHJ test variables was assessed using Pearson's correlation coefficient (r) with Holm's correction applied to statistical significance account for multiple comparisons. The results were interpreted according to recommendations from scientific literature (29) with the following criteria: 0 indicating no correlation, 0.1–0.29 as small, 0.3–0.49 as moderate, 0.5–0.69 as large, 0.7–0.89 as very large, and 0.9–1 as a perfect correlation. Finally, a multiple stepwise regression analysis was performed to identify the hip and trunk strength variables (predictors) that were the strongest predictors of the SLHJ variables (dependent variables). Predictors were included only when their contribution was significant at an alpha level of p < .05. Durbin–Watson statistics and collinearity tests were also performed. We set the thresholds for presence of collinearity at five for variance inflation factor. Additionally, a visual inspection of a scatterplot of residuals was done to confirm homoscedasticity of the residuals. For all analyses, the threshold for statistical significance was set at p < .05.

While the SLHJ test is well established as a reliable and valid tool for assessing unilateral leg power and functional symmetry (7, 8) the addition of directional variables such as side deviation from the expected jump trajectory and jump angle was intended to capture more complex aspects of neuromuscular control, particularly in the frontal plane. However, the results of our study revealed lower than expected intra-session reliability for these directional variables without major differences between preferred and non-preferred legs. Regardless of the leg, jump distance exhibited good-excellent (ICC_2.k = 0.87–0.93) reliability, while side deviation and jump angle (ICC_2.k = 0.33–0.70) demonstrated moderate to poor reliability. These findings emphasize the need for cautious interpretation of side deviation from the expected jump trajectory outcomes, despite their potential biomechanical relevance. This is consistent with earlier evidence suggesting that directional control during dynamic tasks is more variable and influenced by multiple interacting factors including motor coordination, balance, and attentional strategies (16, 20, 30). As such, although side deviation from the expected jump trajectory may provide additional qualitative insight into movement strategy, it cannot yet be considered a reliable outcome measure for individual monitoring without further standardization. One possible explanation for the lower reliability of the jump angle variables is that small differences in jump distance and side deviation values between repetitions (i.e., the numerator and denominator when calculating the angle) can result in greater relative uncertainty in the ratio, yielding a metric that may reflect a different construct. These findings are consistent with previous research indicating that ratio-based metrics often exhibit lower reliability than their constituent measures because variability from both components is combined, increasing measurement error (31). We should also note that jump distance increased significantly with the number of jump repetitions, whereas this was not the case for the directional measures of the SLHJ. This increase may reflect familiarization or potentiation effects across repetitions (32). Averaging three repetitions, as performed in our study, is recommended to further reduce the noise-to-signal ratio (33, 34), that is, to reduce the random error associated with a single repetition and thereby improve the credibility of the results. As the majority of jumps in handball are performed using a single leg, typically contralateral to the throwing arm, it could be speculated that this preferred push-off leg would demonstrate higher reliability (i.e., more consistent performance) across repeated jump repetitions. However, this was not confirmed in the present study, as only minor differences in reliability parameters were observed between the preferred and non-preferred legs. These findings indicate that the same testing protocol can be reliably applied to assess SLHJ performance in both legs of elite handball players, for example, allowing coaches and sports scientists to evaluate SLHJ performance in a single session without requiring extra familiarization for the non-preferred leg.

Although hip and trunk muscles are known to contribute significantly to jump distance (5) and to pelvic stability and directional control during unilateral movements (17, 18), the correlations observed in our study were lower than expected. Specifically, no significant correlations were found for the preferred leg between SLHJ and strength variables. And multiple regression analysis revealed that only adduction T_max was a significant predictor of preferred leg jump distance, explaining 6.3% of the variance. This suggests that factors other than hip and trunk strength, such as inter-muscular coordination (35), may contribute to jump performance more than strength variables.

The contribution of maximal hip adductor strength to the preferred leg SLHJ distance is an interesting finding, to the authors' knowledge not previously reported for a single horizontal jump performed on one leg. Maximal hip adductor strength likely contributes both to horizontal (propulsive) force generation through hip extension and to pelvic stability in the frontal plane during unilateral push-off. The adductor magnus functions as a hip extensor when the hip is flexed (36), a position resembling the semi-squat posture observed during the transition from the eccentric to concentric phase of the SLHJ. In this context, it assists the gluteus maximus and hamstrings in producing hip extension force (37), thereby enhancing horizontal propulsion during the take-off phase. During unilateral tasks, the adductors also play a key role in stabilizing the pelvis and maintaining femoral alignment together with the hip abductors (38). This coordination counteracts excessive hip abduction range of motion that could impair kinetic-chain energy transfer between joints during push-off action. Our results are similar to those of Unal-Suzer et al. (38), however, their findings relate to a consecutive single-leg triple-hop distance rather than the SLHJ distance examined in our study. In their study, maximal hip adductor strength explained 50% of the variance in jump distance, considerably more than in the present study. This may emphasize the greater contribution of maximal hip adductor strength to jump performance during more intensive eccentric–concentric actions, likely due to its role in pelvic stabilization and the generation of higher muscle forces during consecutive single-leg landings and push-offs. Furthermore, adequate adductor strength supports dynamic balance and intersegmental coordination, both of which are essential for maintaining jump trajectory control and effective landing mechanics. This pattern suggests that muscles responsible for frontal-plane control may play a compensatory role when neuromuscular control is challenged, consistent with previous reports highlighting the biomechanical importance of proximal muscle groups in segmental alignment and energy transfer (5). It may also be relevant that adductor T_max in our study exhibited greater variability among participants (CV = 22%) compared with, for example, abduction T_max (CV = 17%), potentially making it a more sensitive indicator of strength deficits and, consequently, SLHJ performance.

For the non-preferred leg, one significant correlation was observed for jump distance and one for side deviation. Multiple regression analyses supported correlation analysis findings, showing that flexion RTD predicted non-preferred-leg jump distance (explaining 10% of the variance), whereas extension T_max and abduction T_max together predicted side deviation (14% of variance explained), and extension T_max alone predicted jump angle (8.4% of variance explained). These results indicate that hip muscle strength is a stronger determinant of single-leg jump performance for the non-preferred leg compared with the preferred push-off leg. Another noteworthy finding is the correlation between hip flexion RTD and jump distance. While hip flexors are not primary contributors to propulsive momentum during jumping, it may be speculated that some participants adopted a technique involving a forceful upward pull of the knee toward the trunk after take-off, generating additional momentum. This could represent a compensatory strategy for suboptimal jump technique or comparatively lower strength of the knee and ankle extensors in the non-preferred push-of leg. Although the explained variance was smaller, these findings partially align with those of Unal-Suzer et al. (38), who found hip flexion RFD to be a significant determinant of triple-hop mechanical work (37% of variance explained). This finding may also be related to adaptations from the frequent use of the handball approach jump shot technique, in which the non–push-off leg is explosively flexed at the hip during take-off. Over time, this repeated movement may lead to increased explosive and maximal strength of the non-preferred leg hip flexors in handball players. Consequently, when performing the SLHJ in our study, players may have leveraged these adaptations to enhance jump distance.

Furthermore, participants with stronger hip extensors and abductors tended to jump more medially than the expected trajectory using non-preferred leg. This finding may be explained by the combined action of the gluteus maximus (the primary hip extensor) and gluteus medius (the primary hip abductor) (37). When these muscles contract simultaneously during single-leg push-off, their resultant force vector acts diagonally, directed backward and outward relative to the pelvis. Because the foot is fixed on the ground, the equal and opposite ground reaction force is directed forward and slightly inward (medially), propelling the body toward the midline. Consequently, stronger individuals in these muscle groups may generate greater diagonal push-off forces, producing a more medial jump trajectory. This pattern likely reflects a hip-dominant propulsion strategy among these participants, where enhanced extensor and abductor strength contributes to stability and force production at the expense of a perfectly straight trajectory.

The absence of associations between lateral trunk flexor strength and SLHJ variables likely reflects the stabilizing, rather than propulsive, role of these muscles during the jump. Lateral trunk flexors help maintain segmental alignment and efficient force transfer without directly contributing to propulsion. Moreover, the static nature of the isometric trunk test likely failed to capture the dynamic eccentric–concentric actions required in ballistic movements (20, 21). This aligns with prior evidence indicating that isolated isometric strength measures are weak predictors of dynamic jump performance (39, 40). Importantly, intervention studies have shown that improving hip muscle function can meaningfully alter landing strategies and reduce frontal-plane loading (6), underscoring the functional importance of these muscles despite the limited predictive value of static strength measures for single-leg jump distance in our study. Finally, the use of isometric testing conditions may partly explain the small-to-moderate correlations observed, as such assessments do not capture the concentric and eccentric dynamics, timing, and intermuscular coordination required during ballistic tasks like the SLHJ (5, 12). Interestingly, despite years of sport-specific handball training that predominantly involves single-leg jumping, hip strength was a weaker predictor of jump performance for preferred push-off leg. It could be argued that continuous unilateral jumping during handball training would enhance hip and trunk strength and be reflected in superior single-leg jump performance. However, this does not appear to be the case. Instead, other factors, such as jump coordination, may have a greater influence on performance of the preferred leg. Conversely, jump distance on the non-preferred leg may reflect hip strength more strongly, likely due to less optimal intramuscular coordination or jump technique. These findings indicate that, in practice, both legs should be assessed. Sport-specific asymmetry therefore exists and should be considered; however, optimal thresholds for reducing injury risk or improving bilateral performance (41) remain to be established for SLHJ test and should be examined in future research.

Several limitations should be acknowledged when interpreting the present findings. First, the modified SLHJ protocol allowed unrestricted use of the arms during take-off and landing, which increased the handball-specific execution of the test and made it more comparable to the actual movement demands in team handball. However, this may also have introduced greater variability and contributed to the poor reliability of directional variables. Future studies could therefore consider a standardized, hands-free version to better isolate lower-limb and trunk control. Due to the greater variability of the results, we suggest that future research examining directional outcomes should include more than three repetitions to further reduce the noise-to-signal ratio and improve the credibility of the results (33, 34). Nevertheless, the optimal number of repetitions remains to be determined and should be explored in future studies. Second, the use of isometric strength testing may not fully capture the dynamic nature of force production and control during jumping. Incorporating more dynamic and sport-specific strength assessments could improve predictive value. Additionally, the hip RTD results showed lower reliability (greater variability between repetitions) compared with T_max results, which may have made it harder to detect true relationships with jump performance, despite averaging multiple repetitions. Furthermore, the SLHJ was performed from a standing position, which may not accurately reflect typical handball game situations (e.g., approach jumps). Regardless of the observed differences in strength predictors between limbs (where only one predictor was identified for the preferred leg) it can be speculated that this test may not be sufficiently specific to capture handball-specific differences in strength adaptations between limbs. Third, although statistically significant, the predictive values of the measured strength variables to jump variables were relatively low (up to 14% of the variance), suggesting that jump distance and side deviations from the expected jump trajectory are influenced by multiple factors beyond isolated muscle strength. Lastly, while the sample consisted of elite male team handball players, generalizability to other sports, female athletes, or sub-elite populations remains uncertain. Given the playing positional demands in team handball, future research may also consider analyzing differences in jump mechanics and control between playing positions, especially since previous studies have shown clear anthropometric and physical distinctions across positions (1, 4).

Despite the observed limitations, the findings of this study suggest that the modified SLHJ test, which incorporates both traditional jump distance and novel side-deviation variables, may provide valuable insights into jump directional control during unilateral tasks. While the directional variables demonstrated lower reliability, their potential to reflect neuromuscular deficits and compensatory strategies warrants further investigation. The multiple small-to-moderate associations observed between hip and trunk strength and SLHJ outcomes highlight the importance of a multifactorial approach when evaluating performance and injury risk, with separate consideration of the preferred and non-preferred jump legs. The modified SLHJ may serve as a practical, field-based screening tool for identifying jump-related compensatory strategies associated with hip strength, particularly in the non-dominant leg, in handball players. Finally, it should be emphasized that the present findings are based on a cross-sectional design rather than a longitudinal one. To confirm whether improvements in hip strength influence modified SLHJ outcomes for preferred and non-preferred legs, interventional studies are required. This test represents an initial step toward a simple, field-based assessment of jump performance that simultaneously reflects hip strength, particularly in the non-dominant leg. With improved standardization and further validation, especially of the directional variables, the test could evolve into a more comprehensive tool for performance profiling and injury prevention strategies in elite team sports.

The modified SLHJ side-deviation and jump-angle measures in the non-preferred leg may help identify hip strength–related factors that are not captured by jump distance alone. However, due to their lower reliability, coaches and clinicians working with handball players should interpret SLHJ directional outcomes with caution, particularly when using them to monitor progress or inform return-to-play decisions. In addition to jump distance, averaging more than three repetitions appears necessary to obtain reliable results, regardless of the tested leg; however, future studies are required to confirm this recommendation. Hip adduction T_max and hip flexion RTD were predictors of jump distance for the preferred and non-preferred legs, respectively. Furthermore, hip extension T_max predicted a more medial jump trajectory in the non-preferred leg. These findings suggest that handball players' push-off leg preference influences SLHJ outcomes; therefore, both legs should be assessed and interpreted accordingly.

The current version of the SLHJ may, in handball practice, serve as a field-based general movement screening test. Its use should be combined with other functional assessments, such as evaluations of landing mechanics or trunk control. The modified SLHJ may help identify specific hip strength–related factors that are not captured by jump distance alone. However, any conclusions regarding hip strength or strength deficits derived from jump distance and directional measures, including deviations from the reference values presented in this study, should be confirmed using laboratory-based strength testing methods before drawing definitive conclusions or implementing training or rehabilitation interventions.