Inter-Limb Asymmetries in Volleyball Players: Differences between Testing Approaches and Association with Performance.

In this study, we investigated the prevalence of inter-limb asymmetries in young volleyball players and assessed the differences in the outcomes of different strength and power tests. The study sample comprised of 54 young volleyball players (25 males). Both limbs were tested for single-leg jumping for distance (forward and lateral single jump and triple jump forward for distance), single-leg vertical counter-movement jump (CMJ), change-of-direction (CoD) ability with 90 and 180° turn tests, unilateral maximal isometric knee extension torque, rate of torque development (RTD), and rate of torque development scaling factor (RTD-SF). For all tests, inter-limb asymmetry indexes were calculated. The average magnitude of the inter-limb asymmetries varied substantially (2.0-31.2 %) among different outcome measures. The agreement in the categorization of participants into ''symmetrical'' or ''asymmetrical'', based on the >10% threshold, was very poor in general, with the exception of the outcomes within the same task (e.g. CMJ power and CMJ force). Similar findings were found for the agreement on the direction of the asymmetries. Inter-limb asymmetry in RTD-SF was weakly associated with the CoD performance (r = 0.30; p = 0.031). Multiple strength and power testing protocols are needed to obtain a comprehensive overview of athlete's imbalances. The commonly accepted 10 % threshold for classification of individuals as asymmetrical should be reconsidered and reinvestigated. RFD-SF is suggested as a novel outcome measure that can provide additional information to researchers and coaches.