Is the 10% Asymmetry Threshold Important in Team Handball? Interlimb Asymmetry and Threshold-Based Performance Analysis in Lower-Limb Functional Tests

Background: Asymmetry in unilateral functional performance may affect both performance outcomes and injury risk in elite athletes. Understanding the relationship between asymmetry ratios and performance parameters in handball players can inform training and monitoring strategies. This study aimed to investigate the relationship between asymmetry ratios obtained from unilateral functional performance tests in elite male handball players and to determine the effect of a 10% asymmetry threshold on performance outcomes. Hypothesis: Asymmetry ratios above 10% in lower extremity functional tests negatively influence performance outcomes in elite male handball players. Study Design: Cross-sectional study with randomized measurements. Level of Evidence: Level 3. Methods: A total of 41 elite male handball players (age, 20.98 ± 2.15 years; height, 185.90 ± 7.58 cm; weight, 92.61 ± 14.72 kg; body mass index, 26.76 ± 3.52 kg/m 2 ; training experience, 11.27 ± 3.45 years) participated voluntarily. Lower extremity strength was evaluated using vertical jump (VJ), counter movement jump (CMJ), and 5 single-leg hop tests (SLHTs): single hop for distance (SH), triple hop (TH), crossover hop (CH), medial side triple hop (MSTH), and 90° medial rotation hop (MRH). Dynamic balance was assessed via the Y balance test (YBT). Participants were classified according to a 10% asymmetry threshold for comparison. Results: Moderate positive correlations were observed between asymmetry ratios in certain multidirectional jump tests and dynamic balance parameters ( P < 0.05). Significant differences between the left and right sides were observed in the VJ, CMJ, SH, TH, MRH, and anterior (ANT) scores ( P < 0.05). Participants within the <10% asymmetry threshold outperformed the >10% group across all tests. Notably, effect sizes were large (d = 0.85-2.62) for VJ, CMJ, SH, MRH, ANT, and posteromedial scores ( P < 0.05). Conclusion: A 10% strength asymmetry ratio represents a critical reference point in elite male handball players. Systematic monitoring of asymmetry ratios is important not only for injury prevention but also for optimizing performance outcomes. Clinical Relevance: Identifying and correcting strength asymmetry, and maintaining them below the 10% threshold, can improve performance and reduce the risk of injury in elite handball athletes.