Lower-limb joint kinetics and their contribution to attacking arm hand velocity during the aerial phase of the volleyball jump serve

In volleyball, the jump serve is a fundamental and widely employed serving technique. A high attacking arm’s hand velocity is a critical determinant for the effective execution of this technique. While previous studies have highlighted the importance of trunk and upper limb movements in influencing hand velocity during the aerial spiking phase, the contribution of lower-limb kinetics remains insufficiently understood. The present study characterised lower-limb kinetics (attacking and non-attacking legs) during the aerial spiking phase of the jump serve and examined the associations between relevant kinematic and kinetic variables and the hand velocity. Seventeen male professional volleyball players participated in this study. Three-dimensional coordinate data were collected using a motion capture system (200 Hz). Kinetic and kinematic variables from take-off (TO) to ball contact (BC) were calculated, and Pearson product–moment correlation and stepwise linear regression were employed to identify factors associated with the hand velocity at BC. During the aerial spiking phase, the peak forward inclination angular velocity of the pelvis was significantly correlated with the attacking arm’s hand velocity at BC. The peak hip flexion moment and positive joint power of the non-attacking leg were also significantly correlated with the hand velocity at BC. The peak knee extension moments and positive joint power of both legs demonstrated additional significant correlations. A stepwise regression model (adjusted R² = 0.532, p = 0.002) included two significant predictors of hand velocity: peak pelvic forward inclination angular velocity and peak hip flexion moment of the non-attacking leg. The findings suggest that enhancing forward pelvic tilt through contraction of the non-attacking leg’s hip flexor is essential for achieving high attacking hand velocity at BC. Additionally, generating mechanical energy by exerting the knee extensors of both legs contributes to enhancing attacking hand velocity.