Does the 10% Asymmetry Threshold Matter? Effects of Lower-Limb Asymmetries on Jumping and Agility in Basketball

Background: Lower-limb asymmetry is linked to injury risk and may impair performance, yet evidence in basketball is inconsistent. A commonly cited 10% threshold is proposed as critical, but its practical relevance in basketball-specific tasks remains unclear. This study examined the effects of asymmetry on vertical jump and agility performance in basketball players, with particular focus on the 10% threshold. Methods: Male university basketball players (n = 20) completed unilateral jump tests (single-leg countermovement jump, single-hop, triple-hop, 6 m hop) and a bilateral COD (change of direction) test to quantify asymmetry. Basketball-specific performance was evaluated using the Lane Agility Test and bilateral countermovement jump. Asymmetry indices were calculated as absolute percentage differences. Paired tests, Welch's t-tests (<10% vs. ≥10% asymmetry), and Pearson correlations were applied. Results: Significant inter-limb asymmetries were detected across all unilateral tasks (large effect sizes). Players with ≥10% asymmetry showed reduced bilateral countermovement jump height compared to <10% (p = 0.039, d = 1.00). Triple-hop asymmetry correlated strongly with slower Lane Agility Test times (r = 0.62, p = 0.003), while single-leg jump asymmetry correlated moderately and negatively with bilateral countermovement jump height (r = -0.46, p = 0.043). No significant associations were found for COD asymmetry. Conclusions: In the present study, inter-limb asymmetries exceeding 10% were associated with impaired vertical jump performance. Triple-hop asymmetry appears most relevant for agility, whereas COD asymmetry may not adequately reflect basketball-specific demands. Monitoring and reducing inter-limb asymmetries may support both performance and injury prevention.