Limb strength asymmetries in elite academy volleyball players: impacts on performance outcomes and insights derived from principal component analysis.

BACKGROUND: The purpose of this study is twofold: (1) to investigate intra- and inter-limb strength imbalances and asymmetries in elite academy volleyball players and their relationships with sprint performance, kinetics, kinematics, countermovement jump (CMJ), squat jump (SJ), and agility performances and (2) to apply principle component analysis (PCA) to identify and better understand the underlying factors that contributing to volleyball performance. METHODS: Thirty-seven elite academy volleyball players completed four testing sessions, assessing pro-agility, sprint, isokinetic strength at 60°s-1 and 180°s-1, and jump performance. Intra-limb asymmetries were calculated using hamstring-to-quadriceps ratios, whereas inter-limb asymmetries were determined using the percentage difference method. RESULTS: At 60°s-1, the intra-limbNDL ratio showed negative correlations with dominant and non-dominant leg ground contact time (GCTDL and GCTNDL, respectively) and a positive correlation with dominant leg flight time (FTDL) and difference between CMJ and SJ heights (CMJSJdiff). Hamstring asymmetry (Hasymmetry) at 60°s-1 correlated positively with 5 m (S5m) and 20 m (S20m) sprint performances and negatively with theoretical maximal velocity (V0) while at 180°s-1, it showed small negative correlations with V0. At 180°s-1, quadriceps asymmetry (Qasymmetry) correlated positively with S5m, relative theoretical maximum force (F0rel), and relative theoretical maximum power (Pmaxrel) but negatively with V0, CMJDL, and CMJ. The PCA results showed that the first four principal components, explaining 51.0% of the total variance and contributing to 88.2% across 12 dimensions, were mainly linked to jump performance, lower-limb strength, sprint performance, and intra-limb ratios. CONCLUSIONS: Intra-limb and inter-limb strength imbalances and asymmetries were found to be weakly to moderately associated with sprint performance, sprint kinetics, kinematics, and jump-related outcomes. PCA results further identified jump variables, lower-limb strength, sprint metrics, and intra-limb ratios as key, interconnected contributors to volleyball performance.